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COMPARISON OF ARTHROPOD ABUNDANCE AND DlVERSlTY IN INTERCROPPING AGROFORESTRY AND CORN
MONOCULTURE SYSTEMS IN SOUTHERN ONTARIO
Heather Dawn Howell
A thesis submitted in confomity with the requirements for the degree of Master of Science in Forestry
Graduate Faculty of Forestry University of Toronto
@Copyright by Heather Dawn Howell, 2001
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FACULTY OF FORESTRY University of Toronto
DEPARTMENTAL ORAL EXAMINATION FOR THE DEGREE OF MASTER OF SCIENCE IN FORESTRY
Examination of Ms. Heather HOWELL
Examination Chair's Signature: &&J%/
We approve this thesis and affim that it meets the departmental oral examination requirements set dom for the degree of Master of Science in Foresby.
Examination Cornmittee:
Abstract
Cornparison of arthropod abundance and diversity in intercropping agroforestry and corn monoculture systems in southem Ontario.
Master of Science in Forestry. 2001. Heather Dawn Howell. Faculty of Forestry, University of Toronto
Arthropod communities were compared between a corn (Zea mays L.)
monoculture and a corn intercropped agroforestry system in southern Ontario during
1998 and 1999. Pan trap data were used in June 1998 while malaise trap data were
examined between June-September 1999. Arthropod abundanœ, representation by
functional group, and hymenopteran family richness and diversity were al1 compared
between the intercropped and the monoculture sites. Differenœs in arthropod
abundance within the intercropped system were also cornPa& between: 1) tree rows
with Norway spruce (Picea abies (L.) Karst.) or btack walnut (Juglans nigra L.); and 2)
tree rows and crop alleys. Taxa such as Opiliones. Dennaptera and Carabidae, which
are associated with organic litter areas that provide shelter during the day, were
significantly higher in the agroforestry system than in the monocuiture system. The
abundance of Hymenoptera, and several of its families, was also significantly higher in
the agroforestry site than in the monoculture site, atthough no differences were
observed in temis of overall family richness and diversity. There were significantly
higher numbers of parasitoids and detritivores in the intercropped agroforestry system
than in the monoculture system, and the intercropped treatment also supported a
significantly higher ratio of parasitoids to herbivores. My results suggest that
intercropping trees with crops such as corn monoculture can improve pest management
by providing habitat to augment natural enemies populations.
Dedication
During the time when I was struggling through this thesis. my little sister
Catherine Middleton and my father-in-law Glen Howell undement their own momentous
challenges after being diagnosed with cancer. I would like to dedicate my thesis to both
of them for having the strength and the courage to overcome their difficult batUe and to
thank them for the love and encouragement that they gave me during the course of this
work.
iii
Acknowledgement I wish to thank the many people who have helped me through this adventure.
f irst and foremost, I would like to extend my sincere thanks and appreciation to rny
supervisor, Dr. Sandy Smith (University of Toronto, Forestry) for providing me with the
opportunity to do this study, in addition to her assistance and understanding throughout
the development of this thesis. I would also like to extend my gratitude to my cornmittee
members for their insightFul guidance and advice: Dr. Andy Kenney (University of
Toronto, Forestry) for expanding my knowledge of agroforestry systems and for his
guidance in statistics; Dr. Chris Darling (Royal Ontario Museum, Toronto) for sharing his
knowledge and enthusiasm for the Hymenoptera; and Dr. Andy Gordon (University of
Guelph) for originally inspiring me to do this study many years ago during my
undergraduate days. Thanks also to Dr. Isabel Bellocq (University of Toronto, Forestry)
for participating in the defence phase and for providing helpful adviœ during the course
of the writing.
I would like to acknowledge the Faculty of Forestry for their financial support
through the Graduate Fellowship in Forestry award.
I am also greatly indebted to many people who have contributed a significant
amount of their time to help me in the field, the laboratory, with the statistical approach
and in other numerous ways. 1 would like to start by giving my deepest thanks to my
brother, Doug Middleton, who volunteered a large number of hours helping me out in
the field and in the laboratory. Large appreciation also goes out to Ping Zhang, Chantal
Lalonde, Robin Thornton, Tanya Campolin and the Kentner family for helping me with
aspects of field work. Special thanks to Naresh Thevathasan. Rick Gray (Agoroforestry
Research Group) and Peter Milton (University of Guelph Agricultural Research Stations)
for their technical support with the research fields. Thank you to Alexi Baev for al1 of his
hard work in the laboratory with arthropod sorting and identification. I would also like to
give a note of appreciation to Deborah Yurman, Bill McMartin and Christine Vance who
gave me advice on my statistical analysis. My sincere gratitude goes to Dr. Fuhua Liu
(Faculty of Forestry), who spent many hours with me, analysing my data together while
patiently helping me to improve my knowledge of statistics. Thank you also to Robert
Moloney (Agriculture Co-op, Barrie), for his expert knowledge on aspects of agronomy. I
would also like to express my gratitude to Wendy Lake, Alison Howell, Rita Howell and
Glen Howell for their careful editing assistance.
Additionally, 1 would like to thank my friends and colleagues in my laboratory and
within the Faculty of Forestry for their warm friendship, advice and support over the
years I have been a student at the university. Most importantly I would like to thank my
family and friends, especially my mom and my grandfather, for their love and
encouragement throughout my thesis work.
1 have reserved my last note of heartfelt love and gratitude for my husband,
Morley Howell, who has given me the tremendous technical, financial and ernotional
support that made it possible to achieve my dream of completing a masters thesis.
Table of Contents
.. Abstract ................................................................................................................................ II ... Dedication ......................................................................................................................... III
Acknowledgement .............................................................................................................. iv
.............................................................................................................. Table of Contents vi ... List of Tables ................................................................................................................... VIII
List of Figures ..................................................................................................................... x Introduction ......................................................................................................................... 1
RATIONALE .......................................................................................................................... 1
Literature Review .................................................................................................... ARTHROPODS IN AGROECOSYSTEMS ..........................................................................
Ecological Funetions of Arthropods in the Agroecosystem .................................. Importance of Hymenoptera in Agroecosystems .................................................
VEGETATIONAL DIVERSITY AND AGROECOSYSTEM STABILITY . Habitats with Adjacent Vegetation ................................. lntercropping Systems ..................................................
AGROFQRESTRY, ~NTERCROPP~NG AGROFORESTRY AND ART Agroforestry in North America ....................................
................
................ .................
'HROPODS . . .................
Intercropping Agroforestry in North America ........................................................... 7 8 Arthropods in Agroforestry Systems ........................................................................ 20
Materials and Methods ...................................................................................................... 27
SITE SELECTION FOR SAMPLING ......................................................................................... -28
DATA ANALY SIS .................................................................................................................. 34 Environmental Data ................................................................................................. 34 Arthropod Abundance ............................................................................................. 34 Arthropod Funetional Group Cornparison ( 1 999 Malaise Traps) ............................. 35 Hymenoptera Richness and Diversity (1 999 Malaise Traps) ................................... 36
Results ............................................................................................................................... 37
GENERAL ARTHROPOD ABUNDANCE .................................................................................... -41 1998 Pan Traps ....................................................................................................... 47 1999 Malaise Traps ................................................................................................. 47
CONIPARISON OF NORWAY SPRUCE-INTERCROPPING AGROFORESTRY AND ............................................................................ CONVENTIONAL MONOCULTURE SYSTEMS 42
...................................................................................................... 1998 Pan Tmps 4 2 ................................................................................................. 1999 Malaise Traps 42
Functional Arthmpoâ Groups and Selected FamiliedOrders from 1999 Malaise ...................................................................................................................... Tmps 48
Hymenopteran Family Richness and Divetsity from 1999 Malaise Traps ............... 61
COMPARISON OF NORWAY SPRUCE AND BLACK WALNUT IN THE ~NTERCROPPING .................................................................................................. AGROFORESTRY SYSTEM -62
....................................................................................................... 1998 Par! Traps 62 ................................................................................................. 1999 Malaise Traps 62
COMPARISON OF TREE ROWS AND CROP ALLEYS IN THE ~NTERCROPPING ........................................................... AGROFORESTRY SYSTEM ..................................... ... -68
....................................................................................................... 1998 Pan Traps 68 ................................................................................................. 1999 Malaise Traps 68
COMPARISON OF ~NTERCROPPING AGROFORESTRY AND CONVENTIONAL MONOCULTURE SYSTEMS .................................................................................................... 77
COMPARISON OF NORWAY SPRUCE AND BLACK WALNUT TREE ROWS IN THE .......................................................................... 1 NTERCROPPING AGROFORESTRY SYSTEM -89
COMPARISON OF TREE ROM AND CROP ALLEYS IN THE INTERcROPPING ................................................................................................... AGROFORESTRY SY STEM -90
....................................................................................................................... Conclusions 93
Literature Sited ....................................................................................................... ...........97 Appendices ............................................................q....................O................................... 1 7
APPENDIX I . NUMBER OF ARTHROPODS IN EACH ORDER/CLASS USlNG PAN TRAPS DURING JUNE 1998 FROM NORWAY SPRUCE AND BLACK WALNUT SITES WiTHIN THE INTERCROPED AGROFORESTRY AND CORN MONOCULTURE SITES. AT THE GUELPH AGRICULTURAL RESEARCH STATION (~=60) ...................................................................... 1 7
APPENOIX 2 . NUMBER OF ARTHROPODS IN EACH ORDER USlNG MALAISE TRAPS DURING JUNE-SEPTEMBER 4999. FROM NORWAY SPRUCE AND BLACK WALNUT SITES WlTHlN THE INTERCROPPING AGROFORESTRY AND CORN MONOCULTURE
........................... STUDY SITES. AT THE GUELPH AGRICULTURAL RESEARCH STATION ( ~ 4 8 ) 118
APPENDIX 3 . NUMBER OF ARTHROPODS IN 61 SELECTED FAMILIES AND 2 SELECTED ORDERS THAT ARE REPRESENTING THE PARASITOID. PREDATOR. POCLINATOR. OETRITIVORE AND HERBlVORE FUNCTIONAL GUlLDSf CAUGHT IN JUNE-SEPTEMBER 1999 IN THE INTERCROPPING AGROFORESTRY NORWAY SPRUCE AND THE CORN MONOCULTURE STUDY SITE. AT THE GUELPH
.............................................. AGRICULTURAL RESEARCH STATION (~=32)
vii
List of Tables Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6
Table 7
Table 8
Table 9
Summary of analysis methods and number of samples for each treatment cornparison and sampling season. ................................................ 31
Selected arthropod families and their associated functional groups' ............. 33
Environmental data collected from a weather station at the Guelph Agricultural Research Station during the summer of 1999. Data based on 3-day mean for each month in which malaise traps were placed in a given treatment. .......................................................................... 38
Mean abundance of arthropod orders collected in pan traps over a 3- day period from a corn intercropped agroforestry site and a monoculture site at the Guelph Agricultural Research Station. 5-8 June 1998 (N=40) .......................................................................................... 43
Mean abundance of arthropod orders collected in malaise traps over a 3-day period from a corn intercropped agroforestry site and a monoculture site at the Guelph Agricultural Research Station, June- September 1999 (N=32). ............................................................................... 44
Mean abundance of arthropod orders collected in malaise traps over a 3-day period from a corn intercropped agroforestry site or a monoculture site at the Guelph Agricultural Research Station, June-
............................................................................... September 1999 (N=32). 46
Arthropod abundance by functional groups from malaise traps operating for 3-day periods in a corn monoculture and an intercropped corn site at the Guelph Agriculture Research Station,
........................................................ Ontario, June-September 1999 (N=32). 49
Abundance of arthropods by functional groups from malaise traps placed three days each month in a corn intercropped agroforestry site and a corn monoculture site at the Guelph Agricultural Research
......................................................... Station. June-September 1999 (N=32). 50
Mean ratio between the number of predators or parasitoids and herbivores collected over three days using malaise traps in a corn monoculture site and a intercropped agroforestry site at the Guelph Agriculture Research Station, Ontario, June-September 1999
......................................................................................................... (N=32). -51
Table 10. Mean abundance of arthropod familiesforders in malaise traps over a 3-day period from a corn intercropped agroforestry site and a corn monoculture site at the Guelph Agricultural Research Station, June-
............................................................................... September 1999 (N=32). 53
Table II. Mean monthly abundance of selected arthropod familiesforders collected in malaise traps over a 3-day period frorn a corn intercropped agroforestry site and a corn monoculture site at the Guelph Agricultural Research Station. June-September 1999 (N=32). .......................................................................................................... 55
Table 12. Mean number of hymenopteran famities in malaise traps from an intercropped agroforestry site and a corn monoculture site at the Guelph Agricultural Research Station. June-September 1999 - (N-32). ......................................................................................................... -61
Table 13. Mean abundance of arthropod orders collected for three days using pan traps in sites either intercropped with Noway spruce or black walnut at the Guelph Agriculture Research Station. 5-8 June 1998 (N=40). ......................................................................................................... - 63
Table 14. Mean abundance of arthropod orders collected for three days using pan traps in sites either intercropped with Nonivay spruce or black walnut at the Guelph Agriculture Research Station, June-September 1 999 (N=32). ................................................................................................ .64
Table 15. Mean monthly abundance of arthropod orders wllected for three days using pan traps in sites either intercropped with Norway spruce or black walnut at the Guelph Agriculture Research Station, June- September 1999 (N=32). .............................................................................. -66
Table 16. Mean abundance of arthropod orders collected in pan traps over a 3-day period in tree rows and crop alleys of sites in the intercropping agroforestry site at the Guelph Agricultural Research Station, 5-8 June 1998 (n=40). ......................................................................................... 70
Table 17. Mean abundance of arthropod orders collected in pan traps over a 3-day period in either the tree rows or crop alleys in the Norway spruce and black walnut treatments of lntercropping agroforestry site at the Guelph Agricultural Research Station. during 5-8 June 1998 (n=40). ................................................................................................. -71
Table 18. Mean abundance of arthropod orders collected in Malaise traps over a 3-day period in tree rows and crop alleys in the intercropping agroforestry site at the Guelph Agricultural Research Station, during
...................................................................... June-September 1999 (n=32).. 72
Table 19. Mean monthly abundance of arthropod orders collected in Malaise traps over a 3-day period the tree rows and crop alleys in the intercropping agroforestry site at the Guelph Agricultural Research Station, during June-September 1999 (n=32). .............................................. 73
Table 20. Mean abundance of arthropod orders collected in pan traps over a 3-day period in the tree rows or crop alleys of sites intercropped with either Norway spruce and black walnut in the lntercropping agroforestry field at the Guelph Agricultural Research Station, during
...................................................................... June-September 1999 (N=32). 75
Table 21. Eight parasitic hymenopteran families with their preferred hostsa, that were found to have significantly higher mean abundances in the intercropped agroforestry site at the Guelph Agricultural Research
..................................................................................... Station, during 1999. 83
List of Figures Figure 1. Sampling design used in: a) the intercropping agroforestry sites with
pan traps during June 1998; b) the monoculture site with pan traps during June 1998; c) the intercropping agroforestry sites with malaise traps during June-September 1999; and d) the monoculture site with malaise traps during June-September 1999. ................................... 29
Figure 2. Relationship between arthropod abundance in malaise traps over a 3-day monthly mean temperature at the Guelph Agricultural Research station during 1999. (n=l 1 )(--regression 95%
.................................................................................................... confidence) 39
Figure 3. Relationship between arthropod abundance in malaise traps mer a 3-day monthly mean percent relative humidity at the Guelph Agricultural Research station during 1999. (n=l 1 ) (---regression
............................................................................................ 95% confidence) 40
Introduction
Rationale
Agroecosystems fonn the dominant ecosystern in southem Ontario, covering
5,201.981 ha or 45% of the land base in the region (Statistics Canada, 1999). The
structure and functioning of the agroecosystem, like al1 natural ecosystems. is
dependent on interactions between soil, water, solar radiation and biological organisms.
Agroecosystems are different from natural ecosystems because they require human
manipulation to keep them functioning artficially in order to meet our needs for food,
fibre and other products (Agriculture and Agri-Food Canada, 1 997a; Altieri, 1 994). Over
the past several decades, growing demand for agricultural products has led to a rise in
high-yield intensive agricultural production throughout the region. This growing
industrialisation of agriculture has raised concems over environmental degradation and
the long-term sustainability of agricultural production in southem Ontario (Xu and Mage,
2001 ; Murray, 1997).
In response to the detrimental environmental effects of agriculture practices,
Agriculture and Agri-Food Canada (AAFC) has set out to find ways to address
environmental sustainability in Canadian agriculture. This directive recognises the
importance of agro-biodiversity. Diverse populations of organisms play an important role
in maintaining agricultural ecological systems (e.g. crop pollination or organic matter
decomposition), and the sustainability of Canadian agriculture and the agri-food sector
depends on conserving this natural biodiversity (AAFC, 2001). One of the many
commitrnents of AAFC is to use agraecosystem indicaton to measure changes in the
organisation and composition of biotic communities in relation to agricultural land
practices and cropping systems (AAFC. 1997b). It has also set out to increase
1
knowledge and understanding of biodiversity in agriculture, to find ways to minimize
adverse impacts of agricuftural practices on biodiversity, and to promote the
incorporation of biodivenity considerations into the fan-level decision making process
(AAFC 2001 ; AAFC, 1997 a).
lntercropping agroforestry is a system that may alleviate agricultural
environmental problems and help increase biological diversity in the agroecosystem.
This system (also known as alley cropping) involves the cutivation of annual or
perennial crops between ro is of trees or shwbs. An annual i n m e is derived from the
agricuttural crop. while a longer-terni income can be gained from the tredshrub
products (USDA, 2000; Hodge et al., 1999; Nair, 1990). The environmental benefits that
have been attribut4 to this systern include: reduction of wind and water erosion, a
modfied microclimate for improveâ crop production, improved utilization of nutrients,
and amelioration of biodiversity (Williams et al., 1 997; USDA, 1 997).
lntercropping has historically been practised in many temperate regions of the
world (Byington, 1990). For example, during the establishment of fruit orchards in
southern Ontario, it is wmmon to cultivate crops such as strawberries (Fragana x
annassa Duch. ) between the rows of the young trees (Leuty, 1999: Gordon and
Williams, 1991). Yet the majority of the scientific research on intercropping agroforestry
has been perforrned in the tropics, creating scientific knowledge that is mainly based on
the conditions of this region (Stamps and Linit, 1999a). Fortunately there has been a
growing interest in temperate intercropping agroforestry over the last 20 yean, and
scientific research examining this systern has increased dramatically (Gordon et al.,
1 997). One important aspect of temperate intercropping agroforestry is its role in the
conservation of biodiverstty within the agroecosystem (Newman and Gordon. 1997).
3
Previous studies have examined the effects of intercropping agroforestry on birds and
earthworms (Price, 1 999; Wlliams et al., 1 996).
Arthropods account for the largest percentage of animal biomass and biodiversity
in the agroecosystem (Paoletti et al., 1992; Pimentel et al., 1992). and they perfotm
many essential roles in most agro-ecological processes (Lasalle. 1999; Swift et al..
1996; Bond, 1993). Their involvement in these processes makes them useful bio-
indicators for assessing agroecosystem sustainsbility (Paoletti, 1 999; van Straalen,
1 997; Holloway and Stork, 1 991).
Unfortunately. very little research has been conducted on arthropods and
intercropping agroforestry systems in the temperate region (Stamps and Linl, 1998).
With only a very few exceptions, the majority of arthropodfintercropping agroforestty
research has taken place in the tropics (Rao et al., 2000; Stamps and Linit, 1998).
Further research is needed if intercropping agroforestry is to be promoted in temperate
agroecosystems. This is especially true because many growers need reassurance that
intercropping agroforestry will not increase p s t problems before they decide to
implement this system (Stamps and Linit, 1998). In addition, research clearly needs to
be conduded in several agro-ecological zones throughout the temperate region. using
different intercropping agroforestry designs. Such research would contribute to our
understanding of how various spatial arrangements and biological/micro-climate
aspects affect the distribution of arthropods.
Research Goal
The primary objective of my study was to examine and compare the arthropod
communities in an intercropping agroforestry system and a conventional monoculhire
corn (Zea mays L.) system in southern Ontario. Several aspects of the arthropod
community were compared: 1) the abundance of arthropods acwrding to their
4
taxonomie order. 2) the abundance of arthropods acmrding to their fundional group. 3)
the ratio between herbivore and natural enemy populations. and 4) famiiy richness and
divenity in the hymenopteran order.
The secondary objective was to examine how physical aspects of the
intercropping agroforestry field affect the abundance of arthropods within this system.
Arthropod populations were compared between two sites planted with different tree
species. Noiway spruce (Picea abies (1.) Karst) and black walnut (Juglans nigm L.).
Comparisons were also made between the tree rows and crop alieys in the agroforestry
system.
Thesis Structure
This thesis proceeds through five main sections. First. a comprehensive literature
review is provided. outlining some of the broader issues related to arthropods in the
agroecosystem, vegetational diversity, and agroforestry. A description of the materials
and methods forms the second section. This is followed by a resuits section. which
presents findings for each of the three study comparisons. A general discussion of the
effects observed in each of the results sections constitutes the fourth component of the
thesis. The last section concludes the thesis and includes a discussion of future
recommendations.
Literature Review
Arthropods in Agroecosystems
Arthropods play important roles in agroecosystems as dominant pollinators of
crops, natural control agents of many agricuitural pests, and other ôeneficial activities
such as building and renewal of agricuitural soils (Lasalle, 1999; Hill, 1997). lt has been
esthated that arthropod pests destroy 13% of the crops grown world-wide (Pimentel,
1 995). The value of this loss in the United States alone was assessed in 1990 to be
$6.6 billion (Metcalf, 1999). However, the estimated economic value of the services
provided by the beneficial insect groups is much greater. For instance, the value of the
pollination service provided by honey bees in the United States. is estimated b be
between $1.6 and $5.7 billion annually (Southwick and Southwick, 1992).
Arthropods are the dominant phylum in the animal kingdom in ternis of divenity
of species and shear abundance (Price, 1997; Mitchell et al., 1988). In addition,
arthropods are also the dominant fauna within the agroecosystem, with the largest
biomass and diversity (Paoletti et al.. 1992). Surveys in temperate and tropical
agroecosystems have found from 262-1000 species of arthropods per hectare, making
up an estimated 1000 kg of fresh weight biomass per hectare (Pimentel et al., 1992).
Many factors influence arthropod population dynamics within agroecosystems.
including conventional agricultural practices (e-g. annual cropping systems), which often
lead to frequent intense disturbanœ. These disturbanœs hinder the survival of various
arthropods, including many beneficial organisms. They also allow more adaptable
arthropod species to thrive. such as many agricuttural pests (Letoumeau, 1998).
Practices such as soi1 tillage. the use of fertilisers, soi1 fumigation, and the use of
pesticides, have al1 been found to affect the abundance and diversity of arthropods in
5
6 the agroecosystem (Noms and Kogan, 2000; Kromp, 1999; Kross and Schaefer, 1998;
Bwij and Noorlander, 1 992; Paoletti et al., 1992; Wnter et a/. , 1 990; Stinner et al.,
1990, 1986). Arthropod populations can also be affected by the structure of the
agricultural landscape. These factors include sire and shape of agricultural fields as
well as the composition and the architecture of the vegetation and its surrounding
habitats (Gurr et al.. 1998; Fry, 1995; Hoit et al., 1995; Landis, 1994).
Arthropod populations are very useful biological indicators to measure the effeds
of d ifferent ag ricultural pradices and landscapes because they are affected by changes
within the agricukural environment. Arthropods are diverse, abundant, ecologicaliy
important, plus easy to collect at low cost (Finnamore, 1996). The combination of these
factors means that they are commonly used in ealogical and agricultural research
studies (Paoletti et al., 1992) and can be used to compare intercropping agroforestry
with conventional monoculture cropping in ternis of sustainability and biological
diversity.
Ecological Functions of Arairopods in the Agroecosystem
Arthropods can be classified into different functional groups according to their
feeding behaviours or by their interactions with other organisms or elements within the
ecosystem. They are arranged into trophic groups or trophic levels according to their
feeding relationships in the ecological community. with plants at the first level,
herbivores at the second level, and carnivores and parasitoids at the third level (Price,
1997). In addition, arthropods can be categorised into guilds depending on the feeding
method they use in exploiting a common resource (Root, 1973). For instance,
herbivores can be divided into subgroups such as sap-feeding and strip-feeding (Krebs,
1994). LaSalle (1 999) groups arthropods living in agroecosystems into five functional
7 groups: pollinators. predaton, parasitoids. herbivores and detritiiores. For the purpose
of my research here, arthropods have been classified into similar groups as those
proposed by Lasalle (1 999).
Pollinators
Man y hig her-level plants (ang iosperms) within the agroewsystem are dependent
on arthropod pollinators for fertilisation because they transport pollen from the stamen
of one flower to the stigma of another fiower (Neff and Simpson. 1993). The production
of rnany economically important food, fibre, and forage crops rely on pollination by
arthropods, with the exception of cereal crops, which are all wind-pollinated (Borror et
al., 1989). Arthropods that are involved in pollination include Diptera (flies), Coleoptera
(beetles), Lepidoptera (moths and buttemies) (Wallace et al., 1991 ). and most
importantly, members of the Apoidae superfamily (bees) of the Hymenoptera (Neff and
Simpson, 1993; O'Toole, 1993).
Hen5ivores
Herbivores play a central role in agroecosystems as consumers of plants and as
food for predaton. Approximately one quarter of al1 insect species are phytophagous
(Strong et a/., 1984) and can constitute between 45.80% of individual arthropods found
in some agroecosystems (Nentwig, 1998). Herbivores are found in many orders
including : the Acarnia (mite), Diptera, Hymenoptera, Thysanoptera, Phasmida,
Lepidoptera, Orthoptera, Demaptera, Hemiptera, Coleoptera, Lepidoptera and
Hornoptera (Letourneau, 1997), with the last three k i n g the most notable (Barbosa.
1998). Although they are generally considered pests within the wntext of agricultural
production, some herbivores can also be viewed as biological control agents of weeds
(Lasalle. 1999). Unfortunately, not al1 weed-consuming arthropods are beneficial
8 because many feed on weeds for one part of the season and later move on to consume
cuitîvated crops (Norris and Kogan. 2000).
The most notable arthropd herbivores in the com~ropping systems of southem
Ontario are: the European corn borer (Pyralidae: Ostrinia nubilalis (Hubner)); corn
rootwoms (Ch rysomelidae: Diabmtica spp. ); the corn leaf ap hid (Aphidae:
Rhopalosiphurn maidis (Fitch)); and the a rmyworm (Noctuidae: Pseudaletia unipuncta
(Haworth)) (OMAFRA, 1999; Rice, 1996).
Detritivoms
Many arthropods within the agroecosystem are important wmponents in soil,
plant and animal decomposition. These detntivores help to increase the rate of litter
breakdown by shredding and masticating plant tissues, thereby increasing the litter
surface area available for fungi and bacteria (van Straalen. 1997). Such arthropods also
help ameliorate soi1 aeration and soi1 moisture by tunnelhg within the humus layers and
decaying roots (Marshall et al., 1 982). Collembola (springtails) and Acamia (mites) are
the principal detritivores within agroecosystems (Wardle et a/. . 1 999). althoug h other
arthropods such as lsopoda (woodlice) (Paoletti and Hassall, 1999) and Dipoloda
(rnillipedes) (Cloudsley-Thompson, 1958) are also involved in the decomposition
process.
Predators
Predators arthropods are exceedingly beneficial in agroecosystems because
they help to naturally regulate populations of herbivores (Booij and Noorlander. 1992;
Luff, 1983). Many predatory species are renowned for their ability to suppress
phytophagous pest populations in agroecosystems. For example, ladybird beetles
(Coccinellidae) have been used in several biolog ical control programs (1 perti. i 999).
9 Even though some predators may have only minor impact on an individual basis. their
overall population can contnbute greatly to pest mortality (Barbosa and Wratten, 1998).
In general, predators tend to be more polyphagous than parasitoids and will feed on
many different kinds of arthropod prey, including beneficial species. The ability to eat
many diff'erent kinds of prey allows some predators to survive through limited prey
conditions (Lasalle, 1999). Orders and families of some important predatory groups
within agroecosystems include: Diptera (Ernpididae, Syrphidae, Dolichopodidae,
Asilidae); Arachnida; Hymenoptera (Formicidae. Pornpilidae, Vespidae); Coleoptera
(Coccinellidae, Carabidae, Staphylinidae. Cantharidae); Hemiptera (Anthocoridae.
Nabidae. Reduviidae); and Neuroptera (Chrysopoidae, Hemerobiidae) (Lasalle, 1999;
Stelzl and Devatak. 1 999; Helenius, 1998; Nentwig, 1998; Brothers and Finnamore,
1 993; LaSal te and Gauld, 1 993; Borror et al.. 1 992).
Parasitoids
Like predators, parasitoids play a major role in maintaining the ecological
balance in arthropod populations, and often regulate the number and density of
herbivorous pests (Landis and Menalled, 1 998; Lasalle and Gauld, 1993). Parasitoids
affect their target host by living in or on the body of a single organism during their larval
stage. eventually killing it or suppressing its growth (Price, 1997). In most cases,
herbivorous arthropods are attacked by more than one parasitoid species, while many
parasitoid species attack more than one host (Altieri et al.. 1993). The members of the
order Hymenoptera make up the largest proportion of the parasitoid group, although
other important parasitoid species can be found in the order Diptera (Lasalle. 1999). for
example the family Tachinidae (McAlpine. 1981).
Importance of Hymenoptera in Agroecosystems
The order Hymenoptera is one of the rnost diverse and abundant orders within
the class Insecta. With well over 115, 000 described species in 80 different families
(Lasalle and Gauld, 1903). this order represents approximately 14% of al1 the narned
insect species in the world (Danks, 1988). Within temperate regions, the Hymenoptera
is the richest in ternis of species (Lasalle and Gauld, 1993). In fact, there are
approximately 7, 000 species of Hymenoptera in Canada. representing one quarter of
the country's total number of scientifically named insects (Mason and Huber, 1993).
In addlion to their divenw, the Hymenoptera are also recognised for their
different functional roles within ecosystems. The majority of families are
entomophagous (feeding on inseds) either as parasitoids or predators (Masner et al.,
1 979). while others are phytophagous (plant feeders) or xylophagous (wood eating)
(Lasalle and Gauld, 1993). Some families include a wide range of feeding habits, such
as the family Formicidae (ants), whose members feed on other insects, fungi, plants,
plant sap. nectar, honey dew, flesh of dead animals, etc. (Holldobler and Wilson,l990).
The importance of the Hymenoptera in agroecosystems is highlighted by the
variety of crucial roles its members play. For example, the principal pollinators of
fiowering plants are bees, including honeybees. bumblebees and solitary bees
(O'Toole. 1993), while the dominant parasitoids are also hymenopterans (Lasalle, 1999;
Altieri et al., 1993). In addition, many species are important predaton, keeping
arthropod populations balanced within agroecosystems. In fact, the predators and
parasitoids from this order have k e n found to interact with more arthropod prey
species than any other terrestrial arthropod order (Lasalle and Gauld, 1993).
Because of their importance in the fundioning of agroecosystems, the order
Hymenoptera can be considered important indicators of ecosystem health and stability.
As such. they are often used to examine the effects of agricuitural practices, such as
soi1 tillage (Lobry de Bniyn. 1999) and pesticide and fertiliser usage (Paoletti. 1999;
Jensen. 1997; Bohac and Fuchs, 1991) on agricultural sustainability. In addition, they
can provide information on changes in structural components such as the quantity and
influence of natural habitats in agroecosysterns (Svensson et al.. 2000; Unruh and
Messing, 1999; Bruck and Lewis. 1998; Lagerlof et al.. 1992).
My study focuses on the order Hymenoptera because of their significant and
broad-ranging functions. Specifically, my thesis examines differences in the abundance.
richness and diversity of hymenopteran families between a monoculture field and one
intercropped wit h trees (agroforestry).
Vegetational Diversity and Agroecosystem Stability
The theory that increases in vegetational diversity will lead to ecosystem stability
through a reduction in pest outbreaks has been widely debated (Risch et al.. 1983). It
has frequently k e n offered as an explanation for the apparent high levels of herbivore
damage in monocuitures and less severe or infrequent injuries in natural polycutture
systems (Letoumeau, 1997; van Emden and Williams, 1974).
There are three main ecological hypotheses that expfain why pest populations
might be lower in multi-species plant environments: 1) resource concentration; 2) plant
association resistance; and 3) the natural enemy hypothesis (Altieri, 1994). The
resource concentration hypothesis developed by Root (1 973) states that specialist
herbivores are more likely to detect and stay in habitats where their host plants are
concentrated and where their reproductive success is likely to be greatest. A reduction
in the density of the host plant resource, an alteration in the spatial arrangement of the
12 host plant. or the interference of increased non-host plants abundance, are al1 thought
to inhibit herbivores from locating and exploiting their host plant resource.
Convenely, Tahvanainen and Root (1972) hypothesised that there exists a plant
association resistance to herbivore populations, possibly developed by means of the
complex vegetational structure, chernical environment and associated patterns of
microclimates in habitats where plant species are intemixed. Association resistanœ is
thought to be important to herbivores that are relatively small and dependent on
oifactory mechanisms to find their plant hosts. Non-host plant odoun may attract
herbivores and therefore act as decoys for the host plants (Pnce, 1997) or mask the
odours emitted from the host plant (Alieri, 1994).
Finally, the natural enemy hypothesis suggests that natural enemies will be
more abundant and diverse in vegetationally diverse environments than in monocultures
(Root, 1973). Vegetational diventty is thought to provide better environmental and
microclimatic conditions that help sustain or increase predator and parasitoid
populations. These conditions include greater availability of resources such as prey,
hosts, pollen and nectar, shelter, breeding and nesting sites, and improved microclimate
(Risch, 1981). Natural enemies are also thought to have access to a greater variety of
hosts or prey over a longer period of time in such habitats as wmpared to monocultures
(Andow and Risch, 1985).
The debate surrounding the validity of these three ewlogical hypotheses has
producad extensive literature review (Smith and McSorley. 2000; Tonhasca and Byme,
1994; Andow, 1991 ; Sheehan, 1 986; Kareiva, 1983; Risch et al., 1983). Andow (1 991 )
found that 53% of the studies he reviewed showed herbivores were less abundant (on a
population per plant basis) in polycultures than in monocultures. In 15-1 8% of the
cases, herbivores were more abundant, while 9% showed no difference and 20% had a
13
varied response. In Russell's (1989) work, 50% of the studies found higher herbivore
mortality from predation and parasitism in vegetationally diverse systems than in
monocultures, however, he believed that most studies lacked adequate controls,
thereby preventing conclusive findings. On the other hand, Russell found that the
natural enemy hypothesis and the resource concentration hypothesis probably acted as
complernentary mechanisms in reducing the number of herbivores in the polycultures,
and that they should be dealt with simultaneously to achieve maximum herbivore
wntrol.
Habitats with Adjacent Vegetation
In traditional agricuttural fields where crops are grown annually, there are regular
and significant disturbances to arthropod communities through activities such as tilling,
planting, spraying, fertilising and harvesting (Aitieri, 1994). Some arthropods, such as
herbivorous pests, have adapted well to such disturbad habitats (Letoumeau, 1 997).
Other arthropod groups, such as the parasitoids, do not fare as well because they lack
adequate food and microhabitat resources (Landis and Menalled, 1998).
Wthin agricultural landscapes, arthropods appear to depend upon uncultivated.
vegetationally diverse habitats adjacent to agricultural fields. lnterest has been growing
in studying how these areas influence the density and distribution of arthropods within
agroecosystems (Burel and Baudry, 1995). A common view is that vegetationally
diverse habitats surrounding an agricultural field play an important rote in decreasing or
stabilising pest populations, while augmenting and conserving populations of beneficial
arthropods (Landis et al., 2000; Fry, 1995). These field margin environments are
considered beneficial habitats for many arthropods because they provide permanent.
undisturbed and sheltered sites for ovewintering, feeding and reproduction (Burel and
14 Baudry, 1995). These margins are also thought to be important reservoirs for beneficial
insects to redonise agricultural fields (Dennis and Fry, 1992). Unfortunately, many
farmen view field edges as areas that harbour agricultural pests (Marshall and Smith,
1987; van Emden, 1981).
Many studies have examined the use of uncultivated field boundaries by various
arthropod communities, such as butterfiies (Dover et al.. 2000; Feber et al., 1996).
Woody borders (Holtand and Fahrig, 2000). weedy headlands. and grassy ditches
(Macleod, 1999; Thomas and Marshall, 1999; Varchola and Dunn, 1999; Hassall et al.,
1992; Kromp and Steinberger, 1992) are sorne of the habitats that have been studied to
detennine how agricultural landscape structures influence arthropod communities. Many
bordering areas supply critical arthropod habitat for food and shetter because they are
composed of a variety of plants that flower at different times over the year (Delaplane
and Mayer. 2000; O'Twle, 1993; Banaszak, 1992; Lagerlof et al., 1992). These areas
are ako vital for natural enemies because they provide alternative hosts or prey during
times of low pest host density, as well as pollen and nectar for adutts (Barbosa and
Wratten, 1998; Bugg and Pickett, 1998; Corbett, 1 998; Gurr et al., 1 998). Uncultivated
areas also provide stable, undisturbed refuges for predators and parasitoids to
oveminter, nest or rest (Landis et al., 2000; Beane and Bugg, 1998; Ferro and McNeil,
1998).
lntercropping Systems
While a traditional agricultural landscape provides a small degree of undisturbed.
vegetationally diverse habitat in adjacent areas, additional habitats can be created
directly in the agricuttural field. lntercropping is one way to accomplish this. Examples of
this technique include: allowing long grassy ridges to bisect fields (Netwig et al.,
15 1998;Thomas et al.. 1992), harvesting two different annual crops at separate times. and
undersowing different crop species (Helenius, 1998; Coll, 998).
Research on hedgerows has shown that some natural enemies do not venture
far into adjaœnt agricuitural fields. but instead stay close to the woody edges of the
rows (Lewis, 1969b). Further work on grassy within-field habitats has found that these
'islands' provide protected corridors for predatory arthropods, which allows for rapid
colonisation into adjaœnt agricuttural fields (Lys and Nentwig. 1994, 1992). These
grassy stnps do not appear to increase populations of pest species. and populations of
some species actually decline due to the improved balance of herbivores and natural
enemies (Nentwig et al., 1 998).
lntercropping agroforestry is another method that may produce simibr effects on
arthropod communities as the grassy field stnps. Rows of woody plants placed across
an agricuitural field can create beneficial within-field habitat for arthropod communities,
and improve vegetational diversity. When compared to other intercropping techniques.
this design provides better habitat for an assortment of arthropod communities. both in
time and space (Stamps and Linit, 1998). Woody plants are superior to smaller plants
because they provide a larger habitat space with greater architectural wmplexity, and
thereby have a greater effect on the microclimate of the surrounding areas (Lewis,
1969a). Woody plants also provide a more stable environment for arthropods over an
extended period of time because they tend to live longer than other herbaceous plants
(Stamps and Linit, 1998).
In addition to enduring and expanded habitat space, many woody species are
alternative food sources for arthropod communiües (Crane, 1985; Howes. 1979).
Flowering vegetation in the understory of tree rows provides additional nectar and
pollen sources as well as large amounts of plant biomass for herbivorous arthropods.
16
This in tum becomes habitat for alternative hosts of natural enemies, allowing them to
survive when prey populations are low in adjacent agricultural M d s (Murphy et al.,
1 998).
The in-field habitat provided by woody plants used in intercropping agroforestry
systems has the potential to produœ desirable e M s on arthropod communities.
Therefore, one of the main goals of my research will be to determine l tree rows provide
a beneficial habitat for arthropods by comparing the arthropod populations and pest to
natural enemy ratios between an intercropped agroforestry system and a monoculture
system .
Agroforestry, lntercropping Agroforestry and Arthropods
The practice of integrating trees within agricultural systems. known as
agroforestry. has k e n used around the world for hundreds of yean. It was not until the
late 1970's that interest in the application of agroforestry and scientific research on
agroforestry systems began to fiourish (Nair, 1996). Many practitioners promote
agroforestry as an economic and environmental alternative to conventional agriculture
systems. At the same time. they acknowledge that little is known about how these
systems function. This shortcoming must be addressed in order to promote agroforestry
in agriculture.
One example of this is the need for a better understanding of the biological,
physical and chemical interactions that occur in agroforestry systems (Gordon et al.,
1 997), especially in terms of application and adoptability for specific agricultural
production systems (Raintree, 1990). The advantages and disadvantages of
agroforestry must also be compared to other land-use systems. pnmarily monoculture
systems that currently dominate agriculture and forestry (MacDicken and Vergara,
Agroforestry in North America
Agroforestry is a marriage between the practices of agriculture and forestry. It
has k e n defined as: ". . . a land use that involves deliberate retention, introduction, or
mixture of trees or other woody perennials in croplanimal production fields to benefit
from the resultant ecological and economic interactions." (MacDicken and Vergara,
1990). In NoNi America, there are several different types of agroforestry that fit this
definition. These c m be grouped into one of two categories: agrisilvicutture (crops and
trees, including s hm bs andlor vines) or silvopasture (pasture andlor animals and trees)
(Nair, 1990). The foms of agroforestry commonly practiced in Canada and the United
States include windbreak systems (woody plant barriers used to reduœ and redired
wind), silvopasture (trees grown in pasture with livestock). riparian forest buffers
(streamside forests made up of tree, shrub, and grass plantings), forest farming
(specialty crops grown or harvested from the forest), and intercropping (inter-planting
rows of trees with rows of crops in between) (Williams et al., 1997; Nair, 1996; Byington,
1 990).
Within North America, agroforestry systems are appealing to those looking for
alternative agrïcultural practices that provide improved environmental and economic
sustainability (Kurtz et al.. 1991 ). Some of the beneficial environmental characteristics
of agroforestry include increased wind and water erosion control, reduction of wind
speed, improved soi1 fertility though additional organic matter, microclimate regulation,
improved wildlife habitat, as well as filtering and biodegradation of excess nutrients and
pesticides (MacDicken and Vergara. 1990).
18
Agroforestry systems are also viewed as an opportunistic approach to improving
farm profitability and economic stability (Nair, 1996). Econornic output potential per land
unit area is increased by the combination of product revenue from the trees plus the
crop andlor livestock (Williams and Gordon, 1992; Hoekstra, 1990). Production retums
from crops and livestock can also increase due to the environmental benefits provided
by trees. For instance, yields andlor the quality of valuable horticultural crops c m be
safeguarded by windbreaks, which shelter the crops from abrasion by windblown soi1
(Baldwin, 1988). Agroforestry also provides a way to integrate new products into the
f am enterprise, allowing for financial diversity from a range of different products. This in
tum creates an altemate source of income during financial down times for the main fam
product (USDA, 2000).
Several different tree species are comrnonly used within agroforestry systems in
North America. Black walnut (Juglans nigra L.) and pecan (Carya illinoensis (Wangenh. )
K. Koch) are commonly used in intercropping systems (Nair, 1996; Jackson, 1987) while
long leaf pine (Pinus palustris Miller) and loblolly pine (Pinus taeda L.) are used in
silvopasture systems in the United States (Williams et al.. 1 997). Green ash (Fraxinus
pensylvanica var. subintergenma (Va hl) Fem . ) , Siberian pea t ree (Caragana
aborescens Lamb.), Russian olive (Elaeagnus angustifolia L.), and various poplars
(Poplus spp.) are used in windbreaks and shelterbelts on the Great Plains (Byington,
1990). while Noiway spruce (Picea abies (L.) Karst.) and red pine (Pinus msinosa Al.)
are commonly found in windbreaks throughout Ontario (Williams et al., 1997).
lnbrcropping Agroforestry in North America
Next to windbreaks and silvopastural pradices, intercropping is increasingly
being adopted in North America as an effective agroforestry practice (Nair, 1996).
19 Intercropping agroforestry (alley cropping) is the practice of growing two or more rows of
trees or shmbs, with the rows spaced apart to allow for cultivation of agronomic,
horticultural, or forage crops in the 'alleys' behnreen the rows of woody plants (USDA,
1997). This system has traditionally been used in North America during the
establishment of fruit or nut orchards, where famers grow horticultural crops between
rows of young trees (Nair, 1993). lntercropping agroforestry systems can also be
integrated with other land use pradices, such as Christmas tree production, or for
shifting agricultural land into recreational or urban devetopment (Hodge et al., 1999;
Rule et al., 1 993; W~lliarns and Gordon, 1 992).
Hardwood trees are the most common woody species utilized in intercropping
agroforestry systems in North America (USDA. 1997), with black walnut being the most
widely studied (Nair, 1993). Black walnut is a highly valueâ multipurpose tree that can
produœ timber, nutmeats and nutshells (Garrett et al., 1991). Veneerquality logs can
be marketed for several thousand dollars and nuts of high quality can be sold for $20
per 1 OOlb (US) (Byington, 1990). This tree species is also ideal for intercropping
agroforestry because it is one of the last to develop leaves in the spring, and the first to
defoliate in the fall, allowing for long perÏods of direct sunlight for the alley crops
(Williams et al., 1997). Black walnuts produce very little shade even when the canopy is
fully leafed out. allowing slightly less than 50% full sunlight (Moss, 1964). One drawback
in using this tree species is that it produces juglone, a plant growth inhibitor that may
impede specific broadleaf crops (Hodge et al.. 1999; Farrar, 1 995). although it is
compatible with grasses and other monocot crops (Williams et al.. 1997).
In a recent American survey (Nat. Associ. Res. Cons. Dev. Coun., 2000), 13% of
al1 respondents pradicing agroforestry used intercropping agroforestry techniques. The
main motivation behind increasing the use of intercropping agroforestry systems is
20
usually financial, but other issues such as controlling erosion, improving wilâlife habitat
and irnproving water quality are also important A similar survey with agricuitural
landownen in southem Ontario found that most respondents 'knew very little' about
intercropping agroforestry (Matthews et al., 1993). suggesting that extension education
is needed to promote the benefits of agroforestry throughout the region.
Efforts to further Our understanding of agroforestry systems in Ontario have
originated from the University of Guelph. In 1989, the first North American Temperate
Agroforestry Conferenœ was held there as a forum for researchers, teachers,
extensionists. and praditioners to share up-todate information about temperate
agroforestry, including intercropping agroforestry (Williams, 1991). Several intercropping
agroforestry projects have k e n carried out within the province over the last two
decades, examining physical and chemical interactions within such systems, for
example: nutrients (Zhang , 1999; Thevathasan, 1998); microclimate (Simpson, 1 999,
Williams and Gordon, 1 995); biological interactions with weeds (Kotey. 1997);
earthworrns (Price, 1999); and birds (Williams et al., 1996).
In rny thesis, it was important to include black walnut as the tree species in an
intercropping system because it has been so frequently used and widely studied. A
second species. Norway sprue, a conifer cornmonly planted in windbreaks throughout
the study region. was also included to compare how arthropods respond to different
types of trees within intercropping agroforestry systems.
Arthropods in Agroforestry Systems
In the past, research has conœntrated on tree cultivation and integrating
agroforestry into general agricultural production systems. More recentiy, studies have
focused on biological interactions. such as those including arthropods (Stamps and
21 Linit, 1998) within temperate agroforestry systems (Gordon et al.. 1997). The theory that
agroforestry systems will provide belter habitat for beneficial arttrropods than
monocultures, and the concerns regarding pests within these two systems, must be
addressed through continued research. This will provide basic knowledge on how to
design agroforestry systems to prevent pest problems from developing and to improve
the action of beneficial arthropods (Rao et al., 2000).
As with agricultural or forest entomology, earfy work on arthropods in
agroforestry systems focused on pests, pnmarily those that attack woody plants in
wind breaks, shelterbelts and hedgerows (Green, 1 906). In addition. some studies
examined agricultural pests that overwinter in windbreaks and hedgerows, such as the
wtton bol1 weevil (Anthonornus grandis grandis Boheman) (Slosser et al., 1984;
Reinhard, 1943).
By the late 1960's. with increasing interest in agricultural ecology, different
aspects of agroecosystems were studied in an attempt to improve food production
(Gliessman, 1990). ldeas regarding the structure of the agricuttural landscape and the
effect that it had on arairopods were developed. It was at this time that hypotheses
regarding vegetational diversity were postulated (e.g. resource concentration,
association resistanœ and natural enemy hypotheses).
Some of the first entomological agroforestry studies were conducted in the
1960's to examine insect flight in association with windbreaks (hedgerows). Lewis
(1965) compared the number of arthropods using agroforestry structures to that in a
neighbouring agricultural crop, and found that the diverse flora of the windbreaks helped
to support a greater abundance of insect species than in the crop field. lnsects
appeared to move between these habitats, thereby enriching communities bordering the
field during the spring and summer (Lewis, 1969a). The beneficial shelter provided by
22
the windbreaks enhanced insect populations in the field out to a distance of 3-1 0 times
the height of the windbreak on the leeward side and 1-2 times the height on the
windward side (Lewis, 1969a). During windy days (>2.5 k m ) , he found that the density
of flying inseds on the leeward side increased 2-20 times compared to that during days
when the wind was weak (Lewis, 1969b).
Lewis's work also showed that small migrating airbome p s t species, such as
aphids, were in greater abundanœ near the windbreaks than in the field, probably due
to the taller vegetation, which reduced their dispersal. Lewis (1969b) considered that
windbreaks encouraged some pests, but that their populations were more likely to be
controlled by natural enemies near the windbreaks compared to the same pests in the
centre of the field. He also noted that populations of beneficial species decreased
rapidly with increasing distance from the windbreak. Hence he postulated that the
benefits provided by natural enemies were more likely to exert a check on pest
populations in small rather than large fields.
Wfih increasing interest in the science and application of agroforestry, more
agroforestry entomological research has been presented a international conferences
(Huxley (1983) and Rachie (1983) in Epila, 1986) and within agricultural papers
(Matteson et al., 1 984).
Hetempsylla cubana Crawford, a small psyllid native to Central America, was an
important factor in initiating interest in agroforestry entomology. This pest causes
widespread damage to Leucenea spp., a group of agroforestry trees used in the tropics
(Rao et ai., 2000). The psyllid first appeared in Southeast Asia around l98W 1986
(Shelton and Brewbaker, 1994) and was reported in Tanmnia and Kenya in 1992 (Ogol
and Spence, 1997), where a number of important agroforestty research projects were
carried out by the International Center for Research in Agroforestry (ICRAF). Projects
23 examining the potential of biological control agents for this pest are still ongoing (FAO,
1997; Follett and Roderick, 1 996).
At the same tirne as Heteropsylla was first discovered in Southeast Asia, Epila
(1 986) published a comprehensive paper focusing on agroforestry entomology. Key -
issues, such as the effect of trees in agroforestry systems on arthropod dynamics, as
well as the direction in which entomological agroforestry research needed to be taken,
were addressed. Epila (1986) also started to link the ideas that agroforestry systems
may enhance biological control with nahiral enemies by increasing vegetational
diversity. Most importantly. he pointed out the potential problems of placing trees in
agricuitural systems. For example, oligophagous pests may take advantage of tree
species that are taxonomically related to their target crop pbnts (e.g. trees and crops
that are leguminous)(Rao et al.. 2000). or may use the tees as secondary hosts when
their prefened host is not available. Similarly. pests may become more of a complex
problem in agroforestry systems when perennial plants such as trees are addeâ,
because they allow insect populations to build up over years. Finally, Epila (1986)
pointed out the inherent danger of using non-native introduced plants in agroforestry
systems. because of the increased probability of their being attacked by exotic pests.
In 1988. agroforestry entomology gained international recognition when ICRAF
and the Centre for Applied Biosciences-International (CABI) combined their efforts to
address issues of pest management in agroforestry (Huxley and Greenland, 1989).
Since then, the field of agroforestry entomology has expanded rapidly in the tropics
(Rao et al., 2000; Schroth et al., 2000; Sileshi et al., 2000; Day and Murphy, 1998;
Mchowa and Ngugi, 1994). in the temperate zone (Stamps and Linit, 1998; van Emden,
1998; Vandemeer and Perfecto, 1998; Dix et al., 1997a; Dix et al.. 1995), as well as on
a broader international scale (Dix. 1996; Epila, 1988).
Over the past decade, the majority of arthropod studies have conœntrated on
windbreaks (sheiterbelts and hedgerows) (Stamps and Linit, 1998) either in Canada
(Holland and Fahrig. 2000). the United States (Dix et al., 1997b; Dix, 1991 ; Dix et al.,
1988; Pasek, l988), England (Maudsley. 2000; Gange and Llewellyn. 1989; Bowden
and Dean, 1977; Lewis. 1972.197Oa. 1 WOb. 1969a. 1969b) or France (Petit and
Bure1.1998). A handful of studies have also examined agroforestry systems with respect
to riparian forest buffets (Snell. 1998; Dix et al.. 1 997a; Mallory, 1993) and silvopasture
systems (Singh and Parihar (1997) in Rao et al., 2000).
Research in intercropping agroforestry systems has also been wnducted more
significantly in the tropics than in the temperate zone. This is because of the common
use of this agricuttural system in the tropics (Nair, 1996). and the la& of a large number
of well-designed intercropping agroforestry plots in the temperate region (Stamps and
Linit, 1999a). Many of the tropical studies concentrate on pest insects that attack trees
in the agroforestry system (Sileshi et al., 2000; Ogol and Spence. 1997; Austin et al.,
1995; Mchowa and Ngugi. 1994). In the tropics, important work comparing arthropod
populations within monoculture and intercropping agroforestry systems (e.g. crop pests
and their natural enemies) has also been conducted (Ogol et al., 1998).
Research by Ogol et al. (1999, 1998) has compared natural enemies of the
maize stem borer (Chilo partellus (Swinhoe)) within a maize monoculture and a maize-
leucaena intercropping agroforestry system in Kenya. They found a greater proporoon
of borer eggs preyed upon in the monoculture field than in the intercropped field.
EggAarval and pupal parasitism within the intercropped system at one site was the
same as in !hc monoculture field. but at other sites. parasitism was higher in the
mono cul tu;^ field than in the neighbouring intercropped field (Ogol et al.. 1998). In
contrast, the numbers of stem borer adults and egg masses were significantly higher in
25 the monoculhire fields at both locations than in the intercropped system, and this
resulted in higher damage to the maize plants. Since the abundanœ of natural enemies
was equal in both systems, the authors concluded that the difFerenœ in stem borer
populations was a result of resource concentration rather than natural enemies (Ogol et
al., 1999).
In Kenya, Gima et al. (2000) compared pest and beneficial arthropod
populations beside the tree rows and in the crop alley within bean-intercropping and
maize-intercropping agroforestiy sites, using different tree species over several rainy
seasons. They found sig nificantly hig her infestations of beanflies (Ophiomyia spp. ) next
to the tree row (34%) than further out into the crop alley (25%). although there was no
differenœ observed in size of the b a n aphid populations (Aphis fabae Scopoli).
Significantly lower stem borer and maize aphid (Rhopalosiphum maidis (Fitch))
infestations (21 %) were also reported close to the tree rows in the maize intercropped
agroforestry system than further into the crop alley (30% and 32%, respectively), as well
as significant differenœs in natural enemies. Predatory fadybird beetles were
significantly higher in both the bean and corn crop alleyways. while spiders and
hymenopteran populations were significantly higher closer to the tree rows within the
maize intercropped field. There was veiy little discrepancy in arthropod populations
amongst the different tree species used within the tree rows of the intercropped systems
(Gina et al., 2000).
A few studies have examined arthropods in temperate intercropped agroforestry
systems: three from North Arnerica and one from Great Britain. Two of the American
studies have looked specifically at the distribution of predatory carabid beetles within
hardwood black walnut (Juglans nigra L.) and sweetgum (Liquidambar sfyraciflua L.)
systems intercropped with alfalfa and brome, or corn and switchgrass. (Nelson and
26 Lint, 1999; Ward and Ward, 1999). The other study compared arthropod communities
in a walnut-forage intercropped agroforestry system with arthropod communities in a
monoculture forage field (Stamps et al.. 2000,199913). Using sweep nets, pitfall traps
and vacuum sampling methods, their study found lower numbers of herbivores within
the intercropped systems than in the monoculture system. They also found a
significantly more diverse wmrnunity with a higher ratio between natural enemies and
pests. This research suggests that intercropping agroforestry supports the 'association
resistance" theory in which insect damage is reduced in a vegetationally diverse
cropping system when compared to a single species cropping system.
An intercropped agroforestry system in northem England planted with peas
(Pisum satvium L. cv. Solara) and sycamore maple (Acerpseudoplantanus L.) showed
that the diversity of arthropod taxa was significantly higher in an intercropping alley pea
crop than in a monoculture pea crop (Peng et al., 1993). In this study, the natural enemy
population was 11 % higher in the intercropped alley crops than in the monoculture
crops, with the largest proportion of arthropod pests found in the monoculture system.
The study also found a ratio of natural enemies to pests of 1:1 in the intercropped
alleyway, but 4 :1 in the monoculture area. Evidence from these studies provides dues
as to what can be expected in other ternperate regions.
My research was intended to further Our understanding of arthropod abundance
and divenity for intercropping agroforestry systems in the temperate zone by using a
different collecting technique (i.e. malaise traps). a different crop (i.e. corn). and
different types of tree species (i.e. Norway spruce and black walnut) than have
previously been examined.
Materials and Methods
Site Description
The study was conducted at the Guelph Field Research Station (43O16'30" N.
89O26.35" W). on the eastem edge of the University of Guelph in southem Ontario,
Canada. Two field sites were used in the study: an intercropping agroforestry field
(University of Guelph Agroforestry Research Station) and an adjacent monoculture crop
field. These fields were located on a drumlin oriented north-south. with an average
dope of 6% and sandy loam soi1 texture. Both fields experienced similar macroclimatic
conditions based on hourly information collected by a weather data logger. The two field
sites were subjected to similar cultivation practiœs (land preparation. pbnting time.
fertiliser rate) and were both zero-ülled (P. Milton. Aberfoyle Agriculture Field Research
Station).
The intercropping agroforestry field was 30 ha in size and was established in
1987. It contained approximately 4.000 deciduous and coniferous trees that were first
planted in the spring of 1998 and 1999, 5-6 m apart along 1 - m- wide rows. The tree
rows were parallel to each other and spaced either 12.5 rn or 15m apart. with crop alley
rows planted in between. The 1 ni-wide tree rows were left fallow and the herbaceous
undergrowth was removed periodically by mowing.
The 24-ha monoculture field was separated from the agroforestry field by a 15-m-
wide roadway and was surrounded by grassy ditches on al! sides. Both the corn (Zea
mays L.) variety (Northup King 2409 in 1999 and Novartis Max 40 in 1998) and crop row
alignment (north-west southeast) were identical to that used in the agroforestry field.
Both fields were pfanted with a corn crop on the same day each year, well before
arthropod sampling began: 1 May 1999 and 28 April 1998.
Site Selection for Sampling
The agroforestry field was established in 7987 as a split-split plot experimental
design. to test the effects of between-row spacing and crops on the growth of difFerent
tree species (Gordon and Williams. 1991). Because of this, arthropod sampling sites
were selected to standardize the variables examined. The sites were located in tree
rows with a 20 or 30-in-long grouping of 4-5 m tall trees of the same species; either
black walnut (Juglans nigra L.) or Norway spnice (Picea abies (L.) Karst.) and a 15-m
crop alley of the same agncuttural crop (corn) on boai sides of the tree row. Sampling
sites in the monoculture field were selected 30 m away from the edge of the field to
avoid any influence from the surrounding grassy ditches.
1998 Pan Trap Sarnpling
In June 1998. pan traps were used to sample arthropods in the monoculture and
agroforestry fields. Pan traps are shallow pans, which rely on arthropods falling or flying
into a fluid preservative. These traps collect large numben of arthropods living on or
near the ground such as Coleoptera. Collembola. Homoptera and Arachnida. Some
flying insects. such as small Hymenoptera and Diptera. also land in the traps when
canied by the wind (Ausden. 1996; Bio. Sur. Can.. 1994; Martin. 1977). In the
agroforestry field. 5 pan traps were set out in a straight line transect perpendicular to the
tree row at the four selected black walnut and Norway spruce sampling sites. Two pan
traps were placed on either side of the tree row in the crop alley. at a distance of 3.75
and 7.5 m from the centre of the tree row. The fah trap was placed in the centre of the
tree row (Fig. 1 a)). In the monocuîture field. 5 pan traps were set out in the same linear
design in four selected sampling sites (Fig . 1 b)).
Figure 1. Sampling design used in: a) the intercropping agrofomstry sites with pan traps during June 1998; b) the monoculture site with pan traps during June 1998; c) the intercropping agroforestry sites with malaise taps during June- September 1999; and d) the monoculture site with malaise traps during June- September 1999.
30
The pan traps were smooth-sided plastic containers, 15 x 15 x 5 cm. They were
placed in the ground with their top edges flush to the soi! suace. All pan traps were %-
filled with a mixture of 4:l water: ethanol to act as a preserving agent. Srnall drops of
liquid Sunlight@ detergent were added to each trap in order to lower the surface tension
of the water. A total of 60 pan traps were placed in the fields on 5 June 1998 for three
sampling days. The collected arthropod sarnpies were placed in g las jars filled with
70% ethanol and retumed to the laboratory for sorting and identification.
1999 Malaise Trap Sampling
Malaise traps (Townes, 1972) were used to sample arthropods in 1999. These
wnsisted of open-sided nylon-mesh tents with a collecting jar on top to intercept flying
arthropods (Sharkey, 1996; Bio. Sur. Can., 1994). The slanted roof of the trap directs
arthropods upwards toward the high point of the trap, into the collecting jar. Malaise
traps are very effective in collecting aduît Diptera, Hymenoptera and some Lepidoptera
(Ausden, 1996; Bio. Sur. Can., 1994; Darling and Packer, 1988; Martin, 1977).
Three sites were sampled monthly dunng 1999; a Norway spruce and a black
walnut site in the agroforestry field, and one site in the monoculture field. The number of
sites was reduced in 1999 compareci to 1998, because of the high cost and labour
required for construction of the traps. which meant only four traps could be used. In
order to sample the three sites thoroughly, the four traps were placed in one site for
three days and then moved to the next site. In the agroforestry field, the traps were set
out with hnro traps in the tree row and two traps within the crop alley on opposite sides of
the tree row. They were al1 spaced 7.5 rn from the centre of the configuration and
aligned vertically to the tree and crop rows (Fig. 1 c)). In the monoculture field, the traps
were set up 30 r n from the field edge in the same shape configuration as in the
31 agroforestry sites (Fig. 1 d)). The malaise traps were first set out in the Nomay spniœ
site. The collecting jars were %-filleci with a mixture of 4:1= waterethanol to act as a
presenring agent. After remaining in the field for three days, the collecüng jars were
removed from the malaise traps, and the traps were dismantled and moved to the next
site, the monoculture field. This process was repeated three days later, with the traps
being moved to the walnut site and set up as before. All aroiropod samples were placed
in glass jars f i l ld with 70% ethanol and retumed to the laboratory for sorting and
identification.
The traps were set out 20-29 June, 20-29 July, 12-21 August and 19-28
September 1999. A total of 12 malaise samples were collected each month, for an
overall total of 48 samples over the season.
Table 1. Summary of analysis methods and number of samples for each trealment comparison and sampling season.
(Norway spruce of orders site) vs. monocuîture
1998 Pan traps Treatment Analysis method No. of camparisons samples Ag roforestry -Mean abundanœ 40
Norway spmce -Mean abundanœ 40 vs. black walnut of orders
1999 Malaise traps Analysis methoci No. of
samples -Mean abundanœ 32 of orders -Mean abundanœ of functionai trophic groups -Richness and diversity of hymenopteran families
-Mean abundance 32 of orders
Tree row vs. -Mean abundanœ 40 1 crop alley of orders
-Mean abundanœ 32 of orders
Arthropod Analysis
All arthropods in the pan trap and malaise samples were counted and sorted to
taxonornic Order or Class. depending on the group (e.g. Class for millipedes and
centipedes) using Bomr et al. (1992). Total arthropod abundanœ was then calculateci
for the three sites based on these samples.
Arthropods in different ecologically important functional groups were counted to
be compared between the two agricultural systems. A list was made of 63 arthropod
familieslorders whose primary ecdogical fundion as aduk (larvae only in the case of
Syrphidae) could be categonsed into one of the following trophic gmups: herbivores,
pollinaton, predators. parasitoids and detritivores (Table 2). In cases where taxa were
considered omnivorous or where the familiedorders could be p l a d in more than one
group, attempts were made to select the most appropriate category based on the
predominant function of the taxa members according to the entomological literature
(Goulet and Huber. 1993; Lasalle and Gauld. 1993; Bonor. 1992; McAlpine. 1981 and
Cloudsley-Thompson, 1958). All arthropods from the selected 63 families were further
counted and sorted to taxonomic Family (or Orden) from the 1999 malaise samples
taken from the intercropping agroforestry Norway spruce site and monoculture sites.
Every insect in the order Hymenoptera was identified to family using Goulet and
Huber (1 993) and Borror et al. (1 992); in order to compare family abundance, richness
and divenity within the intercropping agroforestry and monoculture fields.
Table 2. Selected arthropod families and Order Famiiy Trophic
i
-
Arthropod functional group are summarized
QrouP Hymenoptera Braconidae Parasitoid
-
from Goulet and Huber (1993). LaSalle
lchneumonidae Andrenidae Apidae Colletidae Halictidae Megachilidae Sphecidae Forrnicidae Mutilidae Pompilidae Scoliidae Tiphiidae Vespidae Diapriidae Proctotru pidae Bethylidae Chrysididae Dryinidae Platygastridae Scelionidae Aphelinidae Chalcididae Encyrtidae Eucharitidae Eulophidae Eupelmidae Eurytomidae Mymaridae Pteromalidae Trichogrammatidae Ceraphronidae Megaspilidae Eucoilidae Figitidae Tenthredinidae Elasmidae
Coleoptera Carabidae C hysomelidae Coccinellidae
and Gauld. 1993, Borror et al. (1992), McAlpine (1981) and Cloudsley-Thompson (1 958).
Parasitoid Pollinator Pollinator Pollinator Pollinator Pollinator Predator Predator Predator Predator Parasitoid Parasitoid Predator Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Herbivore Parasitoid Predator Herbivore Predator
their associated functional groups' Order Famiiy Trophic
WOUP Di ptera Asilidae Predator
Dolichopodidae Pipunculidae Syrphidae Tachinidae
Hemiptera Anthocoridae Lygaeidae Miridae Nabidae Reduviidae
Homoptera Aphidae Cercopidae Cicadellidae Fufgoroidae
Lepidoptera Noctuidae Pyralidae
Neuroptera Chrysopidae Hemerobiidae
Collernbola Entomobryidae Sminthuridae
Araneae Araneae Opiliones Opiliones Orthoptera Acrididae
Predator Parasitoid Predator Parasitoid Predator Herbivore Herbivore Predator Predator Herbivore Herbivore Herbivore Herbivore Herbivore Herbivore Predator Predator Detritivore Detritivore Predator Detritivore Herbivore
Data Analysis
Environmental Data
Only 4 malaise traps were availabë during the sampling season in 1999. Thus it
was neœssary to move the traps from site to site every three days in order to collect
within each treatment over roughly the same seasonal period. This provided a total
sampling period of 9 days for each month. Weather conditions were likely to change
over this period. and this in tum could influence sampling success. Because of this. the
weather data was first analysed to determine whether there were significant differenœs
between these in terms of variables that might influence arthropod populations. Weather
data were compared between the three dates for each month using a one-way ANOVA
(Statisitica for Windows. StatSoff Inc. 1998). based on log-transfomed data for relative
humidrty and wind speed. Pair-wise comparisons on the means of each factor were then
done using Tukey's test to determine where the dates were significantly difïerent.
The strength of the relationships between temperature or relative humidity and
their potential influence on arthropod abundance was also analysed. This was
performed using a Pearson product moment coefficient correlation (Statisitica for
Windows. StatSoft Inc. 1998). It was important to identify these relationships because
temperature and humidity can commonly influence arthropod activity. By plotting the
relationship, potential explanations for any differenœs in arthropod abundance could be
presented .
Arairopod Abundance
A non-parametric Wilcoxon normal approximation paired t-test (SAS 6.12, SAS
Institute Inc., 1996) was used to analyse the arthropod abundance data. because they
did not meet the assumption of normality, even after log-transformation. Cornparisons
were made in mean abundance of the different arthropod orders between: 1) the
intercropping agroforestry and the monoculture treatments; 2) the Nomiay spruce and
black walnut treatments; and 3) the tree rows and crop alleys in the intercropping
agroforestry field. Monthly difFerences in arthropod abundanœ between these . treatments were also detemined for the 1999 sampling season. l Arthropod Functional Group Cornparison (1999 Malaise Traps)
Differences in the abundance of the five arthropod functional groups between the
intercropping agroforestry and the monoculture sites were determined using non-
parametric Wilcoxon normal approximation paired t-tests (SAS 6.12, SAS lnstitute Inc.,
1996). Selected taxa were arranged into functional groups based on the major
ecological roles played by adults in each family.
Ratios between the entomophagous functional groups (Le. predators.
parasitoids) and the herbivore functional group were calculated in order to determine
whether the ecological balance between predaton and prey differed between the
monoculture and intercropped agroforestry sites. This ratio only estimates an ecological
balance because some of the families that would be representatives of these functional
groups may have k e n missed in the selection process, although efforts were made to
pick as many representative families of the predator, herbivore and parasitoid groups as
possible. For each sample, mean sums of the predators and parasitoids were divided by
the mean sums of the herbivores. These ratios were then analysed using non-
parametric Wilcoxon normal approximation paired t-tests (SAS 6.12, SAS lnstitute Inc.,
1 996) to determine differences between the intercropping agroforestry and the
monoculture sites. A low ratio value would indicate a higher level of prey population to
predatortparasitoid population, and thus, possibly a potential disturbance in the balance
36
of the system. A higher value would suggest that the predatorlparasitoid population was
in better equilibriurn with its prey. I Hymenoptera Richness and Diversity (1999 Malaise Taps)
Hymenopteran farnily richness was wmpared between the intercropping
agroforestry and monoculture treatrnents. Difterences were deterrnined by using the
mean nurnber of families captureci in each sample per treatrnent and then analyzed
using a parametric t-test (Statisitica for Windows, StatSoft Inc. 1998). The divenity of
these families was also detenined using a Shannon diversity index (Hm) (Krebs, f999;
Magurran, 1988). The family diversity was then wmpared between the two field
treatments using a parametric t-test (SAS 6.12, SAS Institute Inc., 1996).
Resu lts
Annual Environmental Conditions
The 1998 pan trap samples were analysed only for the month of June. Weather
variables for this month differed significantly from the sampling dates in June 1999
(Table 3).
In 1999, different weather conditions may have been experienced by the different
treatments because the 4 malaise traps were placed sequentially in each treatment by
month. m e n the weather variables were m p a r e d between treatments over the four
summer months, the majority did not dmer significantly (Table 3). On two occasions,
however, significant differences were observeci. The first was during September when
rnean temperatures differed between the Nomay spnice and black walnut sites. The
second occurred in June, when relative humidity differed between the Norway spruce
and black walnut sites.
The number of arthropods caught was then related to air temperature (Fig. 2)
and humidity (Fig. 3) at the time of capture. Air temperature had a positive effect on the
nurnber of arthropods caugM (Fig 2). whereas humidity had a negative effect (Fig 3).
Table 3. Environmenta I data collected from a weather station at the Guelph Agrlcultural Reclearch Station during the summer of 1999. Data based on 3day mean for each month in which malaise ttaps were placed in a given treatrnent
Mean Mean Year Date Treatment Mean air temperature
(C O)(; + SE) Mean relative precipitation windspeed humidity (%) intensity2 - - (mlsec) -
1998 June 5-8 All treaments 10.0620.41" 61.92 21.62* 1.00 2 0.00' 3.75 2 0.17'
1999 June 20-23 Monoculture 21.29t0.96a*3 27.1922.55a 12.70+0.96a 70.7-6.59 ab* 1.1 320.37 a* 0.60fl.25 a* 23-26 Norway spruce 18.8121 .O0 a* 27.1221.22 a 8.3721 .O0 a 62.4421 .46 b 1.00+0.00 a 0.513.22 a* 26-29 Walnut 19.62+3.04 a* 24.562336 a 15.1623.04 a 83.4326.35 a* 1.32+0.7 O a* 0.91+0.65 a*
July 20-23 Monoculture 22.3320.97 a 29.7921.85 a 15.8420.96 a 73.0321 .O1 a 1 .03+0.16 a 7 .11+0.21 a 23-26 Norway spruce 21.8922.15 a 29.2923.07 a 14.6921 .O0 a 67.8523.94 a 1.0920.38 a 0.5820.20 a 26-29 Walnut 21.92fl.63 a 30.0321 .O8 a 13.2223.04 a 66.51g.36 a 1 .04fl.20 a 0.969.28 a
Aug. 12-1 5 Monoculture 18.21+1.98 a 24.0422.03 a 10.9420.96 a 75.63t0.31 a 1 .16+0.47 a 0.92fl.27 a 15-18 Norway spruce 17.5622.65 a 22.80t2.35 a 13.1721 .O0 a 79.67+7.97a 1.01:'O.lla 0.983.37a 18-21 Walnut 19.6220.90 a 20.0322.74 a 1 1.5023.04 a 83.30t6.13 a 1 .12+0.33 a 0.84fl.23 a
Sept. 19-22 Monoculture 11.87+2.01 ab 19.5223.56 ab 3.3720.96 ab 735827.73 a 1.04+0.20 a 0.72%0.40 a 22-25 Nomay spruce 8.88?3.26 b 15.0122.06 b 1.73+1.00 b 76.1 027.40 a 1 .05+0.23 a 0.90+0.26 a 25-28 Walnut 17.5623.77 a 24.43+1.72 a 11.5623.04 a 81 .0321.37 a 1 .O191 1 a 1 .05+0.04 a
' Means followed by an asterisk for June 1998 and 1999 are significantly different at p=0.05 (t-test). Precipitation intensity was ranked into three categories according to Envimnrnent Canada: 1=light (52.5 mmlh), 2=moderate (2.6 to 7.5mmlh) and
3=heavy (3.6 mdh) (Canadian Atmospheric Environmental Services, 1977). Means followed by the same letter in each column within year and month are not significantly different (P50.05, Tukey's test for paired
comparisons)(n=12).
w
6 8 10 12 14 16 18 20 22 24
3day rnean air temperature (Co)
Figure 2. Relationship between arthropod abundance in malaise traps over a 3- day monthly mean temperature at the Guelph Agricultunl Research station during 1999. (n=l l)(-regression 95% confidence)
72 76 80
3-day mean relative hurnidity (%)
Figure 3. Relationship between arthropod abundance in malaise traps over a 3- day monthly mean percent relative humidity at the Guelph Agricultural Research station during 1999. (n-1 1) (-regression 95% confidence)
General Arthropod Abundance
1998 Pan Traps
In June 5-8 1998, a total of 14,272 arthropods where caught by the pan traps.
These were sorted into 15 orders and 2 classes within the phylum Arthropoda. The
majority of the specimens were from the order Collembola (76.14%. N= 10866). while
the Diptera (1 5.22%. N=2172) made up the second largest group. There were 4,526
individuals from 11 orders and 2 classes collected in the pan traps in the corn
monoculture site. The intercropped agroforestry field yielded 3,958 arthropods from the
Norway spruce site and 5.788 from the black walnut site. Samples in both sites
contained representatives of 13 arthropod orden and 2 classes (Appendix 1).
1999 Malaise Traps
During the sampling periods of June. July, August and September 1999, a total
of 32.059 arthropods from 15 orders where caught by the malaise traps. Almost 50% of
the arthropods were from the order Diptera (47.74%. N= 15306). while the
hymenopteran order had the second highest abundance (18.27%. N=5856). The
intercropping agroforestry field yielded the most arthropods. with 13.884 individuals
representing 15 orders caught in the Norway spnice site, and 9,399 arthropods from 14
orders in the black walnut site. Another 8.821 individuals representing 15 orders were
collected from the corn monocuiture site over the same time period (Appendix 2).
Comparison of Norway Spruce-lntercropping Agroforestry and Conventional Monoculture Systems
1998 Pan laps
The mean abundanœ of arthropods cdlected by the pan traps during 1998
differed significantly between the Nomay spruce-intercropped agroforestry and
monocuiture sites, with a larger number of arthropods caught in the latter (Table 4).
Several significant differences were also found between the treatrnents in terms of
mean abundance of order [e.g. Coieoptera. ûennaptera. Hymenoptera, Opiliones,
Orthoptera and Thysanoptera], with higher mean abundances occumng in the
agroforestry site. Only the order Diptera had a higher mean abundance in the
monoculture than in the intercropped site (Table 4).
1999 Malaise Taps
In 1999, there were no significant differenœs in the mean number of arthropods
captured by Malaise traps between the two treatrnents(Tab1e 5). Similarly, no
significant differences were found between the two treatments in terms of rnean
abundance for many (67%) of the arthropod orders. Exceptions to this were Coleoptera,
Dermaptera. Hymenoptera and Opiliones, which were more abundant in the
intercropped agroforestry than in the monoculture site. Meanwhile. individuals from
order Homoptera were collecteci in the monoculture significantly more than in the
intercropped agroforestry site (Table 5).
Table 4. Mean abundance of arthropod orden collected in pan traps over a 3day period from a corn intercropped agroforestry site and a monoculture site at the Guelph Agricultural Research Station, 5-8 June 1988 (N=40).
Arthropod orders Mean no. arthropodsltrap
Monoculture Ag rofo rest ry z ' P
Araneae Chitopoda Coleoptera Collembola Dermaptera Diplopocla Diptera Hemiptera Homoptera Hymenoptera lsopoda Lepidoptera Odonata Opiliones Orthoptera Thysanoptera
All orders 14.02 2 2.66 9.94 + 2.84 -3.1 1 <0.01 *
' Wilcoxon two sample test, one-sided Pr < Z , df= 19. * Wilcoxon two sample test, one-sided Pr c Z ,df =360.
Significantly different p20.05.
While no significant differenœs were observed in the overall rnean number of
arthropods collecteci from the intercropped or monoculture sites (Table 5). differences
were observed for individual arthropod orders in specific months (Table 6). During June.
Coleoptera, Collembola, Hymenoptera and Orthoptera were al1 significantly more
abundant in the intercropped than the monoculture site. while significantly more
homopterans were found in the monoculture than in the intercropped site. Lepidoptera
in July and. plus Neuroptera and Coleoptera in August were al1 found to be significantly
more abundant in the intercropped than in the monoculture site. During September.
Diptera and Hemiptera were more abundant in the monoculture than in the intercropped
site (Table 6).
Table 6. Mean abundance of arthropod orders collected in malaise traps over a 3- day period from a corn intercropped agrofommtry site or a monoculture site at the Guelph Agriculairal Research Station, JuneSeptember 1999 (N=32).
Month Arthropod Mean no. arthropodsitrap order (; + SE)
Monocuiture Ag roforestry 2 ' P I
June Araneae Coleoptera Collembola Demiaptera Diptera Hemiptera Hornoptera Hymenoptera Lepidoptera Neuroptera Odonata Opiliones Orthoptera Psocoptera Thysanoptera
All orden * July Araneae
Coleoptera Collembola Dennaptera Diptera Hemiptera Homoptera Hymenoptera Lepidoptera Neuroptera Odonata Opiliones Orthoptera Psocoptera Thysanoptera
All orders
0.34 0.03 * 0.05 * 0.10 0.08 0.29 0.03 ' 0.03 ' 0.34 0.17 0.50 0.06 0.05 * 0.23 0.09
0.23
0.39 0.12 0.44 O.? 1 0.17 0.12 0.34 0.08 0.03 0.09 0.24 0.44 0.44 0.37 0.39
0.34
Cont.
September
Coleoptera Collem bola Dermaptera Diptera Hemiptera Homaptera Hymenoptera Lepidoptera Neuroptera Odonata Opiliones Orthoptera Psocoptera Thysanoptera
Table 6 (cont.) Month Arthropod Mean no. arthropodslhap
order (; +SE) Monoculture Ag roforestry Z' P
August Araneae 3.50 1.44 2.00 + 0.41 0.88 0.20 39.75 + 3.77 93.50 + 13.91 -2.17 0.03
All orders
Araneae Coleoptera Collembola Dermaptera Diptera Hemiptera Homoptera Hymenoptera Lepidoptera Neuroptera Odonata Opiliones Orthoptera Psocoptera Thysanoptera
All orders
' Wilcoxon two sample test. one-sided PrcZ, d e 3 . Wilcoxon two sample test. one-sided PrcZ ,dC7 1 . ' Significantly different p50.05.
Functional Arthropod Groups and Selected FamilieslOrdem from 1999 Malaise Tram
Approximately haif of the arthropoâs caught in the Norway spruce and corn
monoculture sites were sorted into a pre-selected group of 61 families and 2 orders
(Araneae and Opiliones). These represented five functional trophic groups; detritivores.
herbivores, parasitoids. predators and pollinators. In total, II ,202 individuals arthrapods
were sorted, with 7,005 from 60 families and 2 orders in the Norway spruce-
intercropped agroforestry site. and 4,197 individuals from 55 families and 2 orden in the
corn monocutture site.
The family with the largest number of arthropods from the selected group was
Entomobryidae (Collembola) (25.8% of the abundanœ of al1 selected families, N=2895),
representatives of the detritivore group. The most abundant herbivore family was
Aphidae (N= 1108), followed in desœnding order by the most abundant parasitoid
Scelionidae (N= 664). predator Coccinellidae (N-98) and pollinator Halididae (N=82)
families (Appendix 3).
Of these five trophic groups. only two differed significantly between the two
treatments (Table 7). Both detritivores and parasitoids were significantly more abundant
in the intercropped than in the monoculture site.
Table 7. Arthropod abundance by functional groups from malaise traps opeating for 3-day periods in a corn monocultum and an intercropped corn site at the Guelph Agriculture Research Station, Ontario, June-September 1999 (N32).
Functional groups Mean no./ trap(x +SE) d f 2' P
Monoculture Ag roforestry
Detritivore 8.352 2.13 59.69 + 25.17 47 -1.84 0.03 ' Herbivore 8.912 2.50 5.21 + 1.16 175 -0.87 0.19 Parasitoid 2.502 0.33 4.49 + 0.48 447 -4.40 e0.01 Pollinator 0.532 0.14 0.91 1' 0.30 79 -0.90 0.19 Predator 4.162 0.59 4.45 + 0.48 255 -1.42 0.08
' Wilcoxon two sample test. one-sidd PrcZ. ' Significantly different p50.05.
Monthly differenœs between the functional groups in the two treatments were
also apparent. The abundance of parasitoids was significantly higher in the intercropped
site than in the monocultute site during June and July. In September. however. there
were significantly more parasitoids in the monoculture field than in the intercropping
site. Detritivores were signifcantly higher in the intercropped site during June while
predators were higher during August (Table 8).
No overall difference was found in the ratio of predators to herbivores between
the monoculture and the agroforestry treatments, but significant differences were seen
for the ratio of parasitoids to herbivores. June was the only month in which the
agroforestry treatment had a significantly higher ratio of both predators and parasitoids
to herbivores. In July, only the ratio between parasitoids and herbivores was
significantly higher (Table 9).
Table 8. Abundance of arthropods by functional groups from malaise traps placed three days each month in a corn intercropped agroforestry rite and a corn monoculture site at the Guelph Agricultural Research Station, June- September 1999 (N=32).
Month Functional Mean no. arthropodsltrap - groups ( X -E)
Monoculture Ag roforestry d f 2' P
June Detritivore Herbivore Parasitoid Pollinator Predator
July Detritivore Herbivore Parasitoid Pollinator Predator
August Detritivore Herbivore Parasitoid Pollinator Predator
September Detritivore Herbivore Parasitoid Pollinator Predator
' Wilcoxon h o sample test, one-sided Pr*Z * Significantly different p50.05.
Table 9. Mean ratio between the number of predatom or pararitoids and herbivores collected over three days using malaise traps in a corn monoculture site and a intercropped agroforertry site at the Guelph Agriculture Research Station, Ontario, June-September tg99 (N=32).
Functional group Mont h Monoculture Agroforestry d f 1' P ratios (X +SE) (i +SE)
Predators: herbivores
Parasitoids: herbivores
June July August September
Overall
June Jul y August Septem ber
Overall
'~aired sample t test. * Significantly different p50.05.
In alrnost one quarter of the 63 selected taxa (representing the five fundional
trophic groups) mean arthropod abundance was significantly higher in the intercropped
site than in the monoculture site (Table 1 O). One of these families was the Opiliones,
representing the detritivore fundional group, was found be significantly different
between the two treatrnents. In addition, 8 out of 28 selected parasitoid families (29%)
had a mean abundance significantly higher in the intercropped site than in the
monocuiture site. These parasitoid families included, Aphelinidae, Chalcididae,
Diapnidae , Encyrtidae, Euwilidae, Eupelmidae, lchneumonidae and Platygastridae. A
similar percentage of predaceous families (5 out of 17 or 29% of the selected predator
families) also had significantly difFerent mean abundances between the two treatments.
Four of these predaceous families. the Carabidae, Pompilidae, Sphecidae, and the
Chrysopidae, were signficantly more abundant in the intercropped site than in the
monoculture site. The Anthocoridae and Cidadellidae familes, representing the
predators and herbivores respectively. were found to have significantly higher means in
the monoculture site than in the intercropped site.
Table 10. Mean abundance of arthropod kmiliedorders in malaise trop over a 3- day period from a corn intercropped agroforestry site and a corn monoculture site at the Guelph Agricultural Research Station, JuneSeptember 1999 (N=32).
Arthropoâ ANiropod Funciional Mean no. arthropodsltrap order familieslorden group (; +SE)
Monocutture Agroforestry 2' P
Araneae Araneae Coleoptera Carabidae
Chysomelidae Coccinellidae
Collembola Entomobryidae
Sminthuridae Diptera Asilidae
Dolichopodidae Pipunculidae Syrp hidae Tachinidae
Hemiptera Anthocoridae Lygaeidae Miridae Nabidae Reduviidae
Homoptera Aphidae Cercopidae Cicadellidae Fulgoroidae
Hymenoptera Andrenidae Aphelinidae Apidae Bethylidae Braconidae Ceraphronidae Chalcididae Chrysididae Colletidae Diapriidae Dryinidae Elasmidae Encyrtidae Eucharitidae Eucoilidae Eulophidae Eupelmidae Eurytornidae Figitidae Forrnicidae
Preâator Predator Herbivore Predator Detritivore
ûetritivore Predator Predator Parasitoid Predator Parasitoid Predator Herbivore Herbivore Predator Predator Herbivore Herbivore Herbivore Herbivore Pollinator Parasitoid Pollinator Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Pollinator Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Predator
Table 10 (wnt.) Arthropod Arthropod Fundional Mean no. arthropods/trap
order familieslorders group (X +SE) Monocuiture Agroforestry Z' P
Hymenoptera Halictidae lchneumonidae Megachilidae Megaspilidae Mutilidae Mymaridae Platygastridae Pompilidae Proctotrupidae Pteromalidae Scelionidae Scoliidae Sphecidae Tenthredinidae Ti phiidae Trichogramrnatidae Vespidae
Lepidoptera Noctuidae Pyralidae
Neuroptera Chrysopidae Hemerobiidae
Opiliones Opiliones Orthoptera Acrididae
Pollinator Parasitoid Pollinator Parasitoid Predator Parasitoid Parasitoid Predator Parasitoid Parasitoid Parasitoid Parasitoid Predator Herbivore Parasitoid Parasitoid Predator Herbivore Herbivore Predator Predator Detritivore Herbivore
' Wilcoxon two sample test. one-sided PrcZ, dft l5. * Significantly different ~50 .05 .
Several representative families differed significantly between the treatrnents in
terms of mean abundance by month (Table II). In June. 9 hymenopteran families and 1
family from each of the Coleoptera, Collembola, Diptera, Homoptera and Orthoptera
orders, differed significantly between the treatments. In July, only 10 families differed
significantly, while in August, only 6 families differed. In September, the abundance of 7
families were significantly different, al1 of them having higher mean abundance in the
corn monoculture site than in the intercropped site, except for lchneumonidae which
had a higher significant abundance in the intercropped site.
Table 11. Mean monthly abundanœ of selectsd arthropod familieslorden, collecteû in malaise tram over a 3day period from a corn intercropped agrofotestry sita and a corn monoculture site at the Guelph Agiicuttural Research Station, JuneSeptember 1999 (N32).
Month Order Arthropod familieslorders
June Araneae Araneae Coleoptera Carabidae
Chysomelidae Coccinellidae
Collem bola Entomobryidae Sminthuridae
Diptera Asilidae Dolichopodidae Pipunculidae Syrphidae Tachinidae
Hemiptera Anthocofidae Lygaeidae Miridae Nabidae Reduviidae
Homoptera Aphidae Cercopidae Cicadellidae Fulgoroidae
Hymenoptera Andrenidae Aphelinidae Apidae Bethylidae Braconidae Ceraphronidae C halcididae Chrysididae Colletidae Diapriidae Dryinidae Elasmidae Encyrtidae Eucharitidae Eucoilidae Eulophidae Eupelmidae Eurytomidae Figitidae
Mean no. arthropodsîlrap ( Z ?SE)
Monoculture Aclroforestrv
Table 11 (cont.)
Month Order Arthropod Mean no. arthropoâs/trap familieslorders (G ?SE)
Monoculture Agroforestry
June Hymenoptera Fomicidae Halictidae lchneumonidae Megachilidae Megaspilidae Mutilidae M ymaridae Platygastridae Porn pilidae Proctotrupidae Pteromalidae Scelionidae Scoliidae Sphecidae Tenthredinidae Tiphiidae Trichogrammatidae Vespidae
Lepidoptera Noctuidae Pyralidae
Neuroptera Chrysopidae Hemerobiidae
Opiliones Opiliones Orthoptera Acrididae
July Araneae Araneae Coleoptera Carabidae
Chysomelidae Coccinellidae
Collembola Entomobryidae Sminthuridae
Diptera Asilidae Dolichopodidae Pipunculidae S yrphidae Tachinidae
Hemiptera Anthocoridae Lygaeidae Miridae Nabidae Reduviidae
Homoptera Aphidae Cercopidae Cicadellidae
0.39 O. 37 0.04 * 0.03 ' 0.50 0.44 0.08 0.29 0.05 * 0.50 0.17 O. 34 0.50 0.50 0.14 0.24 O. 34 0.28 0.34 cont.
Table 11 (cont.)
Month Order Arthropod Mean no. arthropoddtrap familiedo rders (s +-SE)
Monoculture Agroforestry Z' P
July Homoptera Fulgoroidae Hymenoptera Andrenidae
Aphelinidae Apidae Bethylidae Braconidae Ceraphronidae Chalcididae Chrysididae Colletidae Diapriidae Dryinidae Elasmidae Encyrtidae Eucharitidae Eucoilidae Eulophidae Eupelmidae Eurytomidae Figitidae Formicidae Halictidae lchneumonidae Megachilidae Megaspilidae Mutilidae Mymaridae Platygastridae Pompilidae Proctotrupidae Pteromalidae Scelionidae Scoliidae Sphecidae Tent hredinidae Tiphiidae Trichogrammatidae 2.25 + 1.32 Vespidae 1.25 + 0.75
Lepidoptera Noctuidae 1.00 2 0.58 Pyralidae 0.00 + 0.00
Neuroptera Chsrçopidae 1.50 2 0.65 Hemerobiidae 2.752 0.48
Opiliones Opiliones 1.00 +. 0.41 cont.
58 Table 11 (cont.)
Month Order Arth ropod Mean no. arthropodshrap familieslorders (x S E )
Monocuttute Agroforestry 2' P
July Orthoptera Acrididae August Araneae Araneae
Coleoptera Carabidae C hysomelidae Coccinellidae
Collembola Entomobryidae Sminthuridae
Diptera Asilidae Dolichopodidae Pipunculidae Syrphidae Tachinidae
Hemiptera Anthocoridae Lygaeidae Miridae Nabidae Reduviidae
Homoptera Aphidae Cermpidae Cicadellidae Fulgoroidae
Hymenoptera Andrenidae Aphelinidae Apidae Bethylidae Braconidae Ceraphronidae Chatcididae Chrysididae Colletidae Diapriidae Dryinidae Elasmidae Encyrtidae Eucharitidae Eucoilidae Eulophidae Eupelmidae Eurytomidae Figitidae Forrnicidae Halictidae lchneumonidae Megachilidae
0.44 0.20 0.13 0.17 0.03 ' 0.05 * 0.44 0.1 t 0.44 0.44 0.44 0.1 1 0.17 0.50 O. 17 O. 50 O. 50 o. 50 0.05 ' 0.29 0.25 0.31 0.1 1 0.24 0.1 1 0.04 ' 0.50 0.50 0.50 0.50 0.17 0.14 0.50 0.20 O. 50 0.14 0.29 0.1 1 0.50 0.50 0.39 0.24 0.03 ' 0.50
cont.
Table 7 1 (cont. )
Month Order Arthmpod Mean no. arthropodskap familiedorders (2 ?SE)
Monoculture Agroforestry
August Hymenoptera Megaspilidae 1.50 2 Mutilidae 3.00 2 M ymaridae 22.25 2 Platygastridae 0.25 2 Pompilidae 6.25 2 Proctotni pidae 0.00 2 Pteromalidae 3.75 5 Scelionidae 36.50 2 Scoliidae 0.00 2 Sphecidae 1 .O0 2 Tenthredinidae 0.00 2 Tiphiidae 0.25 2 Trichogrammatidae 0.50 2 Vespidae 0.25 2
Lepidoptera Noctuidae 0.50 2 Pyralidae 1.50 2
Neuroptera Chrysopidae 0.00 -, Hemerobiidae 0.25 2
Opiliones Opiliones 0.00 5 Orthoptera Acrididae 0.25 -,
Sept. Araneae Araneae Coleoptera Carabidae
Chysomelidae Coccinellidae
Collembola Entornobryidae Sminthuridae
Diptera Asilidae Dolichopodidae Pipunculidae Syrphidae Tachinidae
Hemiptera Anthocoridae Lygaeidae Miridae Nabidae Reduviidae
Homoptera Aphidae
Cercopidae Cicadellidae Fulgoroidae
Hymenoptera Andrenidae Aphelinidae Apidae
0.50 0.03 " 0.32 0.50 0.50 0.04 ' cont .
Month Order Arth ropod Mean no. arthropodshrap familiedorders ( G %SE)
Monoculture Agroforestry Z' P
Sept. Hymenoptera Bethylidae Braconidae Ceraphronidae Chalcididae Chrysididae Colletidae Diapriidae Dryinidae Elasmidae Encyrtidae Eucharitidae Eucoilidae Eulophidae Eupelmidae Euryîomidae Figitidae Fomiicidae Halictidae lchneumonidae Megachilidae Megaspilidae Mutilidae Mymaridae Platygastridae Pompilidae Proctotrupidae Pteromalidae Scelionidae Scoliidae Sphecidae Tenthredinidae Ti phiidae Trichogrammatidae ~espidae 10.00 2 2.38
Lepidoptera Noctuidae 0.25 + 0.25 Pyralidae 0.00 + 0.00
Neuroptera Chrysopidae 0.25 + 0.25 Hemerobiidae 0.00 +. 0.00
Opiliones Opiliones 0.00 + 0.00 Orthoptera Acrididae 0.00 2 0.00
'-Wilcoxon two sample test, one-sided Pr<Z, df= 3. ' Significantly different ~50 .05 .
Hymenoptenn Family Richness and Diversity from 1999 Malaise Trape
The order Hymenoptera was represented by 37 different families in samples
collected during June-September 1999. In the intercropped site, 36 families were found
while only 30 families were wllected in the corn monocuiture site. In ternis of family
richness, there were no significant difFerences between the mean number of families in
the intercropped and the wm monoculture sites. Sig nificant differences were observed.
however, during June and July (Table12).
Table 12. Mean number of hymenopteran families in malaise tmps from an intercropped agroforestry site and a corn monoculture site al the Guelph Agricultural Research Station, June-September 1999 (N=32).
Month Mean no. hymenopteran familiesltrap (i ?SE)
t ' df P Monoculture Ag roforestry
June 9.50 + 0.87 18.75 + 0.85 -7.61 3 eO.01 * JuSc 17.75 + 1.31 24.75 + 1.25 -3.86 3 e0.01 * A U ~ U S ~ 15.25 5 2.50 17.75 + 2.36 -0.73 3 0.49 September 11.75 + 1.49 8.25 + 1.18 1.84 3 0.12
Atl season 13.56 + 1.10 17.38 + 1.67 -1.90 15 0.07
' Paired sample t test. * Significantly different ~50.05 .
The Shannon diversity index for diversrty of hymenopteran families in the
intercropped site was H'=2.81, while it was H'=2.73 for corn monocuiture site. No
significant difference was found between these indices for either treatment (t=1.12.
Cornparison of Norway Spruce and Black Walnut in the lntercropping Agroforestry System
1998 Pan Traps
Mean arthropod abundance between the black walnut and the Norway spruce
sites was not significantly dflerent in 1998 (Table 13). There were also no significant
differenœs among rnost of the taxonornic groups between the black walnut and Norway
spruce sites, exœpt for Araneae and Coleoptera, both which had higher mean
abundances in black walnut than Nomay spnice site, and Lepidoptera which was
higher in the Norway spruce site than the black walnut site (Table 13).
1999 Malaise Traps
Arthropod abundanœ differed significantly between the black walnut and the
Norway spruce sites (Table 14). Several orden were also significantly more abundant in
the Norway spruce site and none of the orders were significantly different in the black
walnut sites. These orders included; Araneae, Dermaptera, Hemiptera, Orthoptera,
Psowptera and Thysanoptera (Table 14).
Table 13. Mean abundance of arüiropod orders collected for three dayr using pan ûaps in sites either intercropped wlth Nowuay spruce or black walnut at the Guelph Agriculture Research Station, 5-8 June 1998 (N=40).
Arthropod orders Mean no. arthropodsltrap -
(x +-SE)
Noway spruce Black walnut z' P
Araneae C hilopoda Coleoptera Collembola Dermapte ra Diplopoda Diptera Hemiptera Homoptera Hymenoptera lsopoda Lepidoptera Opiliones Orthoptera Psocoptera Thysanoptera
All orders 10.452 2.99 15.31 + 3.38
Wilcoxon two sample test, one-sided Pr < Z , df= 1 9. * Wilcoxon two sample test, one-sided Pr < 2, df=360. * Significantly different p0.05.
Table 14. Mean abundance of arthropod orders collecbd for three days uring pan ûaps in sites either inbrcropped with Nomay spruce or black walnut at the Guelph Agriculture Research Station, June-September 1888 (N=32).
Arthropod orders Mean no. arthropodsltrap (i +SE)
Nonnray spruce Black walnut 2' P
Araneae Coleoptera Collembola Demaptera Diptera Hemiptera Homoptera Hymenoptera Lepidoptera Neuroptera Odonata Opiliones Orthoptera Psocoptera Thysanoptera
All orders2 48.21 + 8.61 32.64 + 4.89
' Wilcoxon two sample test, one-sided Pr < Z , df= 15. * Wilcoxon two sample test, one-sided Pr < Z , dF287. ' Significantly different p50.05.
Mean arthropod abundance differed significantly between the two intercropped
treatments during June, July and August, but not during September (Table 15). In June,
4 arthropod order, Coleoptera, Diptera, Hemiptera and Orthoptera were signifmntly
more abundant in the Norway spnice site, while in the same month Neuroptera had was
signficant more abundant in the black walnut site. Two orden were significantly greater
in the spnice site than the walnut site during July (Araneae and Hemiptera), as well as
two in August (Coleoptera and Neuroptera). In September, arthropod abundanœ of
both Coleoptera and Diptera was higher in the black walnut site than in the Notway
spruce site (Table 15).
Table 15. Mean monthly abundance of arthropoâ orders collected for three days using pan traps in si- either intercropped with Norway spruce or black walnut at the Guelph Agriculture Research Station, June-Septamber 1999 (N=32).
Month Arthropod Order
June Araneae Coleoptera Collembola Dermaptera Diptera Hemiptera Homoptera Hymenoptera Lepidoptera Neuroptera Odonata Opiliones Orthoptera Psocoptera Thysanoptera
All orders
Juiy Araneae Coleoptera Collembola Demiaptera Diptera Hemiptera Homoptera Hymenoptera Lepidoptera Neuroptera Odonata Opiliones Orthoptera Psocoptera Thysanoptera
All orders
Mean no. arthropodsfirap - ( X +SE)
Noway Spnice Walnut
cont.
Tabîe 15 (cent.)
Month Arthropod Mean no. arthropodsltrap order (; LSE)
Norway Spruce Walnut August Araneae 2.00 + 0.41 1.75 2 1.44
Coleoptera Collembola Dermaptera Diptera Hemi ptera Homoptera Hymenoptera Lepidoptera Neuroptera Odonata Opiliones Orthoptera Psocopte ra Thysanoptera
All orders 42.99 2 10.49 21.99 + 6.90
September Araneae Coleoptera Collembola Demaptera Diptera Hemiptera Homoptera Hymenoptera Lepidoptera Neuroptera Odonata Opiliones Orthoptera Psocoptera Thysanoptera
All orders 9.71 + 3.11 31.21 + 10.11
Wilcoxon two sarnple test, one-sided Pr< Z, d t 3 Wilcoxon two sample test, one-sided Pr< 2, df=71
* Significantly different p50.05.
Cornparison of Tree Rows and Crop Alleys in the lntercropping Agroforestry System
1998 Pan Traps
Overall arthropod abundance differed significantly between the tree rows and the
crop alleys in the Norway spnice intercropped site during 1998 (Table16). For the
majority of the taxonomic groups, however no significant difFerences were seen
between the tree row and crop alley, with the exception of Chilopoda, Diplopoda,
Hemiptera and Opiliones (Table 16).
In the Norway spruce site, there were four arthropod orders/cIasses that had
significantly higher means in the tree row than the crop alley; Chilipoda, Diplopoda.
Hemiptera and Opiliones. In the black walnut site, only the Homoptera order had a
significantly higher mean in the crop alley, while four ordenlclasses had significantly
higher means in the tree row, Coleoptera, Collembola. Diplopoda, Diptera, and
Homoptera (Table 17).
1999 Malaise Tnps
No significant differences were observed in the mean number of arthropods
between the tree row or crop alley in the intercropping agroforestry sites (Table 18).
Similarly, no differences were observed between the tree rows and the crop alleys in the
abundance of various arthropod taxonomic groups, with the exception of Homoptera,
which was signficantly higher in the crop alley than the tree row (Table 18).
There was also no significant difference between these two habitats during June,
July or Aug ust, althoug h during September sig nificantly more arthropods were collected
in the tree row than in the crop alley (Table 19). Similarly, no significant differences
were observed between the tree row and the crop alley for the different arthropod
orders in any of the four months, with the exception of Diptera in August and
Collembola. Homoptera and Neuroptera in September (Table 19).
For the individual tree species sites, none of the orders differed significantly
between the tree row and crop alley for the Nomay spruce site, while in the black
walnut site, only Homoptera showed a significant difference between the two locations
(Table 20). Here the mean abundance of homopterans was greater in the crop alley
than the tree row.
Table 16. Mean abundance of arthropod orden collected in pan ûaps over a 3day period in tree rows and crop alleys of sites in the intercropping agroforestry site at the Guelph Agricultural Research Station, 5 8 June 1998 (n=40).
Arthropod orden Mean no. arthropodsltrap (; +SE)
Tree row Crop alley 2' P
Araneae C hilopoda Coleoptera Collembola Demaptera Diplopoda Diptera Hemiptera Homoptera Hymenoptera lsopoda Lepidoptera Opiliones Orthoptera Thysanoptera
All ordersb 1.80 + 0.20
1 W~lcoxon h o sample test, one-sided Pr < Z, df= 19. 2 W~lcoxon two sample test, one-sided Pr * 2, df= 399. * Significantly different p50.05.
Table 17. Mean abundance of arthropod orden collected in pan traps over a 3day period in either the ûee rows or crop allsys in the Nomay spruce and black walnut treatments of lntercropping agroforestty site at the Guelph Agricultural Research Station, during 5 8 Juns 1998 (n=40).
Arthropod Mean no. arthropodshap Mean no. arthropodsltrap ordets (; +SE)
Norway spruce 2' P (i +-SE)
Black walnut Tree row Crop alley Tree row Crop alley
Araneae C hilopoda Coleoptera Collembola Derrnaptera Diplopoda Diptera Hemiptera Homoptera Hymenoptera lsopoda Lepidoptera Opiliones Orthoptera Psocoptera Thysanoptera
' Wilcoxon two sample test, one-sided Pr * Z , df= 9. Significantly different ~50.05.
Table 18. Mean abundance of arthropod orders collected in Malaise traps over a 3day period in tree rom, and crop alleys in the intercropping agroforestry site at the Guelph Agricultural Research Station, during JuneSeptember 1999 (n=32).
Arthropod orders Mean no. arthropodsllrap
Tree row Crop alley
Araneae Coleoptera Collembola Dermaptera Diptera Hemiptera Homoptera Hymenoptera Lepidoptera Neuroptera Odonata Opiliones Orthoptera Psocoptera Thysanoptera
All orders2 36.87 + 6.89 43.97 + ' Wilcoxon two sample test, one-sided Pr < Z , df= 15. * Wilcoxon two sample test, one-sided Pr < Z , df= 287. * Significantly different p50.05.
73 Table 19. Mean monthly abundance of aithropod orciers collected in Malaise tmps over a 3-day priod the tiee mws and cmp alleys in the indemropping agrofomstry site at the Guelph Agriculturol Research Station, during June- September 1999 (n=32).
Month Arthropod Mean no. arthropodsltrap order ( i ?SE)
z' P Tree row Crop alley
June Araneae Coleoptera Collembola Dermaptera Diptera Hemiptera Homoptera Hymenoptera Lepidoptera Neuroptera Odonata Opiliones Orthoptera Psocoptera Thysanoptera
All orders2
July Araneae Coleoptera Collembola ûemiaptera Diptera Hem iptera Homoptera Hymenoptera Lepidoptera Neuroptera Odonata Opiliones Orthoptera Psocoptera Th ysanoptera
AH orders
cont.
Table 19 (cont.)
Month Arthropod Mean no. arthropodsltrap orcîer (X -E)
Tree row C r o ~ allev
August Araneae Coleoptera Collembola Dermaptera Diptera Hemiptera Homoptera Hymenoptera Lepidoptera Neuroptera Odonata Opiliones Orthoptera Psocoptera Thysanoptera
AI1 orders 20.07 5 4.75 44.90 2 11.57
September Araneae Coleoptera Collem bola Dermaptera Diptera Hemiptera Homoptera Hymenoptera Lepidoptera Neuroptera Odonata Opiliones Ort hoptera Psocoptera Th ysanoptera
All orders 11.24 4 4.67 29.68 +. 9.53
' Wtlcoxon two sample test. one-sided Pr< Z,df=3. Wilcoxon two sample test. one-sided P r Z,df=71 Significantly different p50.05
Table 20. Msan abundance of arthropod orders collected in pan traps over a 3day period in the h e rom, or crop alleyr of sites intercropped with either Norway spruce and black walnut in the lntercropping agroforestry field at the Guelph Agricultural Research Station, during June-September 1989 (N-32).
Arthropod orders Mean no. arthropodsltrap -
(X +SE) Norway spruce 2' P
Tree row Crop alley
Araneae Coleoptera Collembola Dermaptera Diptera Hemiptera Homoptera Hymenoptera Lepidoptera Neuroptera Odonata Opiliones Orthoptera Psocoptera Thysanoptera
Mean no. arthropodshrap (; +SE)
Black walnut 2' Tree row Crop alley
Wilcoxon two sample test, one-sided Pr< Z,df=7. ' Significantly different p50.05
Discussion
Environmental Conditions During 1999
Many abiotic factors influence arthropod population dynamics, one of the most
important being weather. Temperature and humidity are two well-known climatic
elements that affect activity and behaviour of these poikilothermic organisms (Weisser
et al., 1997). Optimal temperature thresholds for arthropod activity generally occur
between 10-35OC, aithough many arthropods, such as moths, can fiy when the air
temperature is close to 0°C (Schowalter, 2000; Chapman, 1998). The influence of
humidity on arthropod adivity is atso important, but is generally less pronounœd than
that of temperature (Stein, 1 986).
Families of insects react in different ways to changes in these two weather
variables. For instance, one study examining activity of hymenopteran parasitoids found
that ichneumonids preferred temperatures between 15-21 OC, while braconiâs preferred
temperatures q 21 -7OC. Populations of both these insects decreased when the relative
humidity was < 25% or > 90% (Juillet, 1964). My resuîts are similar to those of Juillet
(1 964, 1960) for parasitic Hymenoptera, showing a positive population response with
temperature but a negative relationship with humidtty.
Given the significant effect of air temperature on arthropod populations, the
Nomay spnice data from September should be regarded cautiously. When this site was
sampled, the mean 3day air temperature dropped below 1 O°C, the commonly accepted
temperature threshold for arthropod activity (Chapman, 1998). Cornpansons between
this site and the black walnut site, or between the monocuiture and intercropped
agroforestry treatments during September, therefore. may sirnpîy be a result of
differenœs in air temperature between the two sample dates.
Similarly, dunng June 1999, relative humidity levels differed between the Norway
spruce and black walnut sampling dates. This means that the significantly higher
numbers of arthropods found in the Norway spruce site could simply be a result of a
difference in relative humidity. The fact that there were no signkant differenœs
between humidity levels during July and August, and the mean number of arthropods
was still higher in Norway spruce than black walnut. suggests that dmerenœs in relative
humidity do not explain the treatment effeds in June. Relative humidity for the two June
dates was also well within the maximum and minimum thresholds set by Juillet (1964)
for Hymenoptera.
Cornparison of lntercropping Agroforestry and Conventional Monoculture Systems
Intercropping rows of trees within a corn crop did not appear to affect the overall
number of arthropods in the agroecosystem, because both the conventional
monoculture and the agroforestry fields had similar densities. This was consistent
across al1 four sampling months in 1999. These findings contrast those of Stamps et al.
(2000) who found significantly higher amounts of arthropods in the monoculture field.
During June 1998, however, there were significantly greater numben of arthropods
coilected in the corn monocutture than in the intercropped agroforestry treatment. This
discrepancy between the 1999 and 1998 results could be due to the different types of
sampling methods used (pan traps for ground arthropods in 1998 versus malaise traps
for aerial arthropods in 1999). If this is correct. then the significant difference between
the two fields in 1998 should be reflected in the number of grounddwelling arthropods
caught in the monoculture and the agroforestry treatments. As none of the primarily
78 grounddwelling arairopoâs (e.g. Chilopoda, Diplopoda, or Isopoda) differed between
the two sites, it is unlikely that the trapping method affecteci the results. Moreover. al1 of
the other taxonomie orden that were significantly different between the two fields in
1998 were also different in June 1999, as well as over the entire season of 1999 (e.g.
Coleoptera. Hymenoptera and Orthoptera). Thus. the discrepancy between the 1999
and June 1998 data is more likely due to the substantially higher number of Diptera
collected during 1998 in the monoculture field.
Although the overall abundanœ of arthropod individuals did not Vary between the
intercropping agroforestry and monoaiiture treatments, this does not provide sufficient
information to perform an accurate assessment of ecological sustainability. Diversity,
taxa richness, and relationships among functional groups are better indicators for
performing such an assessment (Paoletti, 1999; Letoumeau, 1998; Swift et al., 1996;
Altiefi. 1991).
Numerous arthropod orders and families were more abundant in the
intercropping agroforestry field than in the monoculture field. In addition. almost ail of
the orders that were significantly different in the 1999 Malaise traps, were also different
in the 1998 pan traps. Orders that were different included: Coleoptera. Demaptera,
Opiliones and Hymenoptera.
Coleoptera is the second largest arthropod order in Canada in terms of number
of species (Danks, 1988). and its members belong to several different trophic groups.
including herbivores, predators, and detritivores (Lawrence, 1991). The majonty of the
beetles in the monoculture field (71 56) were members of three families (Carabidae,
Chrysomelidae and Coccinellidae). In contrast, these famiiies represented only 43% of
the beetles collected in the agroforestry field. This suggests that the agroforestry site
supported a greater divenity of Coleoptera. This may have been due to an increased
number of microhabitats in the intercropped agroforestry sites. including tree trunks,
canopy. leaf litter, crop alleys, herbaœous understory, and plant species (Stamps and
Linit, 1998).
Ground beetles (Carabidae) seemed to be most favourably influenced by the
microenvironmental conditions in the agroforestry sites. Most memben of this family are
generalist predaton, both as adults and as larvae. prefemng humid. undisturôeâ areas
of leaf litter and other organic debris for development (Lang et al.. 1999; Kromp and
Steinberger, 1 992; Dillion and Dillon, 1972). lntercropping agroforestry systems create
long microhabitat conidors, which allow these predators to access the agricultural fieM
where they can forage for prey (Varchola and Dunn. 1999; Petit and Burel, 1998). This
may explain why the carabids were found in greater numbers (9X higher mean) in the
agroforestry field than in the monoculture field. During my field collections, these beetles
were most often observed hiding on the ground under the dark canopy of the Norway
spruce.
Chrysomelidae (leaf beetles) dominated the beetle population in the agroforestry
field (30%). but was not signifïcantly different from the monoculture field. Chrysomelidae
is a species-rich family in terms of the number of species it contains, and most species
are herbivores feeding on a variety of plants and plant parts (Wilcox, 1 979). This family
had a high abundance in the agroforestry sites because of the habitat provided by the
diversity of plant species in the herbaceous understory, as well as the trees themselves.
One important pest species in the family Chrysomelidae attacking corn in
southern Ontario is the northem corn rootworm, Diabrotica bariben Smith and Lawrenœ
(OMAFRA, 1999). This beetle oveminten as an egg in the soil. emerging in the spring
and causing damage ta the corn roots as larvae in midJune to early August; adults
emerge in eariy to midAugust (ESA, 1999). These beetles were found in both the
80 agroforestry and the monoculture sites. and represented a significant proportion of the
chrysomelids in both fields during August when the aduk were emerging. Almost al1
rootworm eggs are laid in cornfields previousiy planted with corn (OMAFRA. 1999).
Both the monoculture field that was used in 1999. and the crop alleys in the agroforestry
sites during that year had not been planted with corn the year before. Sampling sites in
the agroforestry field, however, were much closer to fields where corn had been planted
in the previous year, than was the monoculture site. Thus, the majority of these beetles
were probably migrants coming into both the agroforestry and monoculture sites. and
the higher numben in the agroforestry field were probably due to its doser proximity to
areas previously planted with corn.
Two orders of omnivorous scavengers were significantly more plentiful in the
agroforestry field than in the monoculhire field: Demptera and Opiliones. The
Opiliones were also found to be more abundant in the tree rows as compared to the
crop alleys in the agroforestry sites.
Only five species of Demaptera Iive in Canada (Danks, 1988). The species most
wmmonly found in Ontario and in my samples, was the European eawig, Fort7cula
auricularia 1. (Vickery and Kevan. 1986). This insed is primarily omnivorous. feeding on
both decaying plant material and small insects (Lamb and Wellington, 1975). It is also
known to feed on living plants when food is scarce (O'Brien. 1 990). Eaiwigs tend to be
noctumal and will seek out shelter in humid areas under leaf litter or in small crevices
during the day. This sheiter protects them from an inhospitable microdimate and
predation. and also provides a location for social interactions to ocair (Lamb and
Wellington, 1975). Feeding activity tends to be uinœntrated in a 50 cm area around the
sheiter. but they will also wander several rneters away within a night (Lamb, 1975).
Female earwigs construct nests in subterranean tunnels or chamben under leaf litter
areas (Lamb. 1976a). The female remains close her nest, pmtecting her brood from
predators and providing the nymphs with food, until they disperse from the nest and
begin to forage independently (Lamb, 1 976b).
Opiliones are also primarily noctumal and live in humid leaf litter or on tree trunks
(Cloudsley -Thompson, 1958). They are opportunistic scavengers feeding on dead
animal material or soft vegetable matter, and prey on small invertebrates such as
springtails, sowbugs, and mites (Halaj and Cady, 2000; Gertsch, 1979). Female
opiliones generally lay their eggs in the soil. under stones and in other rnoist places
(Cloudsley-Thompson, 1 958).
Populations of both Dermaptera and Opiliones may have been higher in the
agroforestry sites because they provided better microclimatic conditions and sheltering
areas than the open monoculture field. Both of these arthropods require humid
environments to prevent desiccation. decaying animal and plant matenal for food, and
sheltered areas in which to lay their eggs or nest. These arthropods may have been
attracted to the tree rows in the intercropping agroforestry site because of: a) the
undisturbed soiVleaf litter areas for their nests. b) the daytime shelter habitat, and c) the
proximity of the sumnding agricultural foraging area. A recent study examining
Opiliones in a soybean field and hedgerow system (Halaj and Cady, 2000) found a
greater abundance of individuals, and a higher proportion of feeding individuals, in the
hedgerow than in the soybean field. These results wrnplement my findings.
The taxon with the greatest difference between the two treatments was the order
Hymenoptera. This order has memben in several functional groups (predators,
pollinators, parasitoids and herbivores), in addition to being one of the most abundant
orders in my samples. A detailed look at this order suggests that they are a key group
wlh some striking differences between the treatments.
82 Some researchers consider the family level to provide a good estimate of species
richness and diversity composition (Williams and Gaston. 1993). My work suggests that
there was no differenœ between the agroforestry and the monoculture sites in tems of
overall hymenopteran family richness and diversity. However. dunng the first half of the
season. hymenopteran farnily richness was higher in the agroforestry sites than in the
monoculture field. The only time farnily richness was greater in the monoculture field
was during September. the period when the data may have been affected by the
differenœ in air temperature between the Norway spnice and monoculture sampling
dates. Henœ the anomalous September result may not have been a treatment effect.
The diversity in behaviour and habitat requirements of hymenopterans makes it
difficuit to explain any observed treatment differences at the order ievel. Their functional
roles. however. may be more illuminating in tems of explaining why they were more
abundant in the agroforestry site.
Parasitoids represented the largest group of hymenopteran families (70%)
caught in the intercropped fields. This is not surprising because parasitic
hymenopterans are wnsidered to be the most species-rich functional group within this
order (Lasalle. 1 993). Eig ht parasitic families (31 %) from this functional group were
significantly higher in the agroforestry site than in the monoculture site. and al1 of these
are known to parasitize hosts from a variety of arthropod orders (Table 21). The
behaviour of these families provides some indication as to why they may have had
greater populations in the intercropped sites. For instance, Diapriidae adults generally
prefer damp shady areas (Masner, 1993). which is a microclimatic environment
provîded within the agricultural field in the understory area of the tree rows (Rao et
a/. ,2000).
Table 21. Eight parasitic hymenopteran families with their preferred hastsa. that were found to have signific~ntly higher mean abundances in the intercropped agroforestry site at the Guelph Agricultural Research Station, during 1999.
Farnily Aduit Host Pupae Host Larvae Host Egg Host Order
Aphelinidae
Chalcididae Diapriidae Encyritidae
Eumilidae Eupelmidae lchneumonidae
Platygastridae
Homoptera Diptera
Lepidoptera Diptera Homoptera Diptera Diptera Homoptera Coleoptera
Diptera Lepidoptera Neuroptera Orthoptera Hemiptera Araneae Hymenoptera Di ptera Coleoptera Coleoptera Diptera Hymenoptera Lepidoptera
Diptera
Lepidoptera Orthoptera
Coleoptera Diptera Lepidoptera Neuroptera Orthoptera Hemiptera Arachnidae Hymenoptera
Araneae
Coleoptera Homoptera
a Goulet and Huber (1 993). Freytag (1 985).
In general, parasitic Hymenoptera are known to be more sensitive to
environmental disturbances than other inseds (Lasalle. 1993). This group as a whole is
known to be affected by rnany factors: a) availability of food for aduits (water, pollen and
nectar), b) availability of altemate hosts. c) availability of habitat (nesting, ovemintering,
refuges, reproduction sites), and d) microclimatic conditions (wind, humidity)
(Tschamtke, 2000; Bugg and Pickett, 1998; Landis and Menalled, 1998). Several
physical characteristics of the intercropping agroforestry field provide many of the
specific requirements of the parasitic hymenopterans, which are not provided by a
conventional monoculture system.
Many aduit parasitoids require fiowering plants for pollen andlor nectar (Attieri,
1994). and flowering vegetation in and around crops has been shown to increase the
parasitism of pest populations (Tschamtke, 2000). Conventional agriculture fields may
84 have flowering plants, but only in the unculüvated field edges (Thomas and Marshall,
1999). In an intercropping agroforestry system, herbaœous flowering plants are
embedded wWin the agricuitural field in the understory of the tree rows. Queen Anne's
lace (Daucus camta L.), bladder carnpion (Silene vulgans Garcke). and butter cup
(Ranunculus acns L.) were common flowering understory plants in my Celd study area.
The proximity of nectarlpollen to the agricultural crop area where the parasitoids may be
searching for hosts is beneficial for the adult parasitoids (Alieri et al., 1993). In addition
to nectar and pollen sources, arthropods wlhin the tree rows can provide alternative
hosts for the parasitoids during times of host scarcity in the agncuitural crop area
(Stamps and Linit, 1998). Hymenopteran parasitoids are quite habitat specific and
prefer to attack taxonomically unrelated insects found in their favoured habitat, rather
than taxonomically related species within different habitats (Altieri et al., 1993)
Parasitoids often have difficulty in establishing populations in annual crop
monocultures because of detrimental and disniptive agricuitural activities (Wratten and
van Emden, 1995). Tree rows in intercropping agroforestry systems are relatively
undisturbed by mechanical equipment, providing a protected and stable overwintering
area for successive generations of parasitoids.
Finally. some of the hymenopteran parasitoids may have preferred the
intercropping agroforestry site because of reduced windspeed between the tree rows
(Rao et al., 2000). which eases fiight activity. lchneumonids for instance. are large wasp
parasitoids capable of directed flight. They tend to be most active in areas of dense
vegetation, where the windspeed is reduced (Juillet, 1960).
Two predaceous hymenopteran wasp families were significantly higher in the
agroforestry site than in the monoculture site. The first. Pompilidae, are well-known
spider predators, stinging and paralysing their prey to supply food for their offspring in
underground nests (Brothers and Finnamore, 1993). The other predaceous family,
Sphecidae, establishes nests in the ground. as well as in hollow plant stems or cavities
in wood (Gauld and Bolton. 1988) and are predaceous on a wide vanety of arthropods,
including Orthoptera, Diptera, Hemiptera and Homoptera (Finnamore and Michener,
1993). Both of these families need abundant prey and undisturbed areas for
underground nesting and overwintering as pre-pupae (O'Neit, 2001). This may partially
explain why their populations were greatest in the intercropped agroforestry sites.
Unlike the monoculture field, where the ground is seasonally disrupted by tilling and
harvesting ections, the intercropped fields have large undisturbed areas within the tree
rows. With nesting sites in the tree rows, these families would have easier access to
their prey in the agricultural crop than if they had their nests only along the edges of the
field. With a lower risk of their underground nests k ing destroyed. populations of these
families are better able to build up over the long term.
None of the pollinator families had higher populations in the agroforestry site than
the monocutture site, nor did the pollinator group as a whole differ between the two
treatments. This was surpnsing because it is generally thought that pollinators in an
agmecosystem are depended on undisturbed marginal areas with a diversity of
flowering plants (Svensson et al., 2000; O'Toole. 1993; Lagerlof et al., 1992) and the
weedy understory of the agroforestry tree row would best meet these conditions. It may
be that pollinators were not really attracted to either of these sites despite the number of
weedy flowering species because both the crops and the trees were wind pollinated.
Further research should be conducted to determine whether a change in the crop or
tree species, to ones more dependent on insect pollination (e.g. from the Rosaceae),
would significantly augment the pollinating guild.
In addition to the number of orders and families with signifmnt population
differenœs between the two fields. two functional trophic groups also had signifimntly
greater population levefs in the intercropped agroforestry field than in the monoculture.
The Crst functional group was the detritivores. The springtails (Collembola) had the
largest abundance within this functionsl group. They are srnall arthropods well known
for their important roles in soi1 respiration and decomposition in agncultural fields
(Lageriof and Andren. 1991). Collembola feed primarily on fungal hyphae and decaying
plant material (Hopkin, 1997) and are thought to improve plant growth through their
feeding on the symbiotic root mycombkae, which in tum stimulates fungal growth
(Lussenhop. 1996). Springtails tend to prefer environments with stable temperatures.
elevated humidity, and high amounts of leaf litterfall of which help stimulate fungal
growth (Hopkin, 1997). Thus it was not surprising that collembolan populations were
sometimes greater in the intercropped sites because of the large amount of leaf Iitter
associateci with the trees and weedy vegetation in the agroforestry sites.
The parasitoids was the second functional group found to be higher in the
agroforestry field than the monoculture field. This group was comprised mainly of
Hymenoptera which, in general, effectively control arthropod populations through their
natural biological control actions, reacting to host population size in a densitydependent
rnanner (Lasalle, 1993). Parasitoids tend to be influenced by food and habitat
availability. as well as microclimatic conditions (Tscharntke, 2000; Bugg and Pickett,
1998; Landis and Menalled; 1998). Thus, my study suggests that the intercropping
agroforestry field was best able to provide the neœssary environmental conditions to
augment parasitoid populations since it could supply pollenlnectar and alternative hosts.
provide the undisturbed ovemintering and nesting areas and provide a more favourable
microclimate (Rao et al., 2000;Starnps and Linit, 1998)
The ratio between parasitoids and herbivores was higher in the intercropping
agroforestry field than in the monoculture field. These resutts are similar to those of
Peng et al. (1993). who found the ratio of natural enemies (predators and parasitoids) to
pests (specific herbivore pests in their study crop), was generalîy greater in an
agroforestry site than in a monoculhiral control area. My study also found significantly
higher ratios of natural enemies (predators and parasitoids) ta herbivores in the
agroforestry site during the earlier part of the corn growing season (June). This also
corresponds with the Peng et al. (1993) study, which found higher proportions of natural
enemies in the agroforestry site than the monoculture during the first part of the pea
crop-growing season. These parallel findings may have k e n related to the proximity of
overwintering habitat and the availability of prey in the agroforestry location.
Only one order had greater abundance in the monoculture field than in the
agroforestry field, Homoptera. All families in this order are herbivores, some important
pests and known transmitters of viral plant disease (Borror et a/. , 1992).
The majority (65%) of the homopterans caught in the monoculture field were
aphids. Many were the corn leaf aphid, Rhopalosiphum maidis (Fitch), an important pest
of field corn in Ontario (Gualieri and Mcleod, 1994). The corn leaf aphid does not
ovenivinter in Ontario, but instead, is carried into m m fields each year by winds from the
south between mid-July and late September (OMAFRA, 1999; Foott, 1977). Excessive
feeding by this aphid results in stunted corn ean and a risk of infection by the maize
dwarf mosaic virus (Rice, 1996). High numbers of this pest occurred in September in
the agroforestry field and most particulariy in the monoculture field. The increase of this
herbivore in September may have been related to the decline of predators and
parasitoids that occurred during the same time periad.
88 Ciccadellidae (Leafhoppers) was the only homopteran famiiy to be caught in
significantly larger numbers in the monoculture field than in the agroforestry field. A
large number of leafhopper species feeâ on different kinds of plants including trees.
grasses and shnibs (Borror et al., 1992). Some species; such as the corn leafhopper
(Dalbulus maidis DeLong & Wolcott) are known to attack corn plants (ESA, 1999;
Hruska and Gomez, 1997) and can be vector of diseases such as the maize streak
disease (Rose. 1 972).
The large concentration of homopterans in the monoculture treatment may have
been a result of the pure stands of uniform, young succulent crop plants in this field.
The resource concentration theory (Root. 1973) states that herbivore specialists (like
the corn leaf aphid) are more likely to stay in habitats where their host plants are
concentrated and where their reproductive success is likely to be the greatest. Several
studies that have compared monocultures with polycultures (like the agroforestry field),
have found that monocultures tend to support a larger number of herbiwres than do
polycuitures (Altieri, 1994). Although I found significantly more homopterans in the
monoculture field than in the agroforestry field, there was no difference between the two
treatments in tems of overalf herbivore abundance.
Anthocoridae, minute pirate bugs, was also significantly greater in the
monoculture field than in the agroforestry field. Both nymphs and adults of this
hemipteran family are generalist predators feeding on a variety of small prey, including
spider mites, insect eggs. aphids, thrips, and small caterpillan (Ketton, 1978). One
species in this family that may be important for corn monocultures is the insidious flower
bug (Onus insidous (Say)) a predator of the corn leaf aphid and eggs and larvae of
other lepidopterous corn pests, such as the corn earworm (Heliothis zea (Boddie)) and
the European corn borer (Ostrinia nubilalis (Hubner)) (Reid, 1991). Coll and Bottrell
89 (1995) also found high numbers of the insidious flower bug within their corn study sites
and relate the high numbers of this generalist predator to food availability (corn pollen
and prey).
Comparison of Norway Spruce and Black Walnut T ree Rows in the lntercropping Agroforestry System
Research in Kenya has shown no e f k d of different tree species on arthropod
abundance in intercropped agroforestry fields (Gima et a/., 2000). In my study however
there was a detectable difference in mean atthropod abundanœ between Nomay
spnice. a wnifer, and Black walnut. a deciduous tree species. in both 1998 and 1999.
These difFerences were reversed between the two yean. with spiders (Araneae) being
higher in pan traps from black walnut dunng 1998 and lower in malaise traps from black
walnut during 1999. It may be that they Iimited data set (one month) in 1998 could
account for these differences and not the trapping method. This suggestion is supported
by the lack of significant differenœs between the two tree species in 1998 for the
predominantly terrestrial orderslclasses like the sowbugs (Isopoda). œntipedes
(Chilopoda) and millipedes (Diplopoda). Further research should examine the two
different sampling methods simultaneously to detemine the cause of this reversal.
Substantial differences in arthropod abundance were obsewed however between
Nomay spruce and black walnut in 1999. Arthropods were more abundant in the spruce
site than the walnut site during the first three months of the season. but not in
September. The notable drop in temperature during September may account for this
lack of signifcanœ in the Norway spnice field, and thus it is not a real treatment effect.
One third of the arthropod orders examined had higher abundance in the Norway
spnice site than in the black walnut site. For the majority of these orden, there was little
difference between population levels in the tree row or in the crop alley. The physical
90 shape of the two tree species may account for the greater number of arthropods in the
Norway spnice site than in the black walnut site. Conifer trees, such as spruce, are
ainical, allowing sunlight to reach understory plants growing between the trees.
Herbaceous plants under umbrella shaped black walnut trees, however, must grow in a
much shadier environment. Potentially this wann and sunny environment with plentiful
amounts of understory vegetation could be one reason why more arthropods like the
herbivore orthopterans, thysanopterans and hemipterans (the latter two taxa have both
herbivores and predators)(Bonor et al., 1992) were found in higher numbers in spruce
than in black walnut. It is possible that the greater number of spiders (Araneae) in the
Norway spruce site was related to the higher number of arthropod prey found there
(Foelix, 1996). On the other had. the greater number of psocopterans in the spruce tree
rows suggests that the tree rows had a large amount of pollen, mold and algae on which
these insects feed (MocMord, 1993).
Cornparison of T ree Rows and Crop Alleys in the lntercropping Agroforestry System
There was some discrepancy between the results found in 1998 and 1999 in
tenns of tree rows and crop alleys. In the malaise samples. arthropod abundanœ was
the same in the tree row as in the crop alley, corresponding to similar work by Lewis
(1 969a. 1969b). Lewis found that windbreak tree rows can influence the abundance and
diversity of flying arthropod populations in an adjacent crop field up to a distance 10
times the height of the tree row. Since trees in my study were only 4-5 rn tall, the
location of the crop alley was well within the zone of influence, and therefore, it is not
surprising that populations were similar between the rows and alleys.
Of the 15 orders studied in 1999, only Homoptera showed any significant
difference, with higher populations in the crop alleys versus the tree rows. These results
91 match closely those of G i m et al. (2000). who found significantly greater populations
of aphids (Homoptera) in corn crop alleys than directiy beside tree rows using elevated
water pan traps in Kenya. One explanation for this difference in homopterans could be
the quality of plants growing in the œntre of the crop alley and homopterans' general
feeding preference for young succulent plant growth. Plants in the œntre of the alley
grow in a less stressful environment than those in the tree row where there is
competition for sunlight and moisture. Thus, plants in the middle of the crop alley are
more succulent and may be preferred by homopterans. Lower numbers of natural
enemies would probably not be a factor in this case, because there was no evidence
that the abundanœ of important predaton such as Araneae and Neuroptera. or the
parasitoids in Hymenoptera. differed between the two locations.
In 1998, more arthropods were caught in pan traps in the tree row than in the
crop alley in contrast to 1999. This difFerenœ could be due to the type of arthropods
caught by pan traps (1 998) versus malaise traps (1 999). Ground-dwelling arthropods,
commonly collecteci by pan traps in the soil, may prefer the type of habitat in tree rows
than in crop alleys. It is also possible that these ground arthropods have lower mobility
and are less able to move between the tree rows-and crop alleys than flying arthropods.
making them less inclined to migrate from their preferred habitat. The type of
orders/classes that differed between the two locations supports this suggestion. For
example, œntipedes (Chilopoda), millipedes (Diplopoda) and Daddy long legs
(Opiliones) were al1 higher in the tree rows than in the crop alleys. These groups are al1
active primadly at night, and prefer moist habitats with a rich humus layer during the day
(Borror et al.. 1 992; Cloudsley-Thompson, 1958). Tree rows provide an ideal habitat for
these arthropods, because: 1) the habitat is not disturbed by mechanical plowing
(Stamps and Linit. 1999); 2) the tree canopy maintains relatively high humidity levels
92 (Rao et al., 2000); and 3) higher leaf litter and understory vegetation (Price, 1999;
Zhang. 1999) provide large amounts of rotting organic material (Vohland and Schroth,
1 999).
Conclusions My work suggests that intercropping agroforestry influences the composition of
the arthropod community as compared to a monocuîture systern. Although overall
arthropod abundance between these two treatrnents was similar. the abundanœ of
many taxonornic groups was significantly different. This had a subsequent effect on the
functional groupings and the ratio between herbivores and natural enemies.
The effect of these differences among the taxonornic groups was clearly evident
for the order Hymenoptera, where noticeably higher populations resulted in greater
numbers of parasitoids in the intercropping agroforestry site than in the monoculture
site. This variation also led to a higher ratio of parasitaid natural enemies to pest
herbivores in the intercropping agroforestry field, suggesting that it provides a better
habitat for these arthropods. The combined attributes of increased food resources,
improved microclimatic environment, and availability of undisturbed habitat. may all
contribute to enhancing the hyrnenopteran community in the intercropping agroforestry
field. My results correspond in part wlh the natural enemy hypothesis, which predicts a
greater abundance and diversity of natural enemies of pest insectr in vegetationally
diverse environments than in monocultures (Root, 1973). My work also supports reœnt
studies by Stamps et al. (2000) and Peng et al. (1 993). which show higher natural
enemy populations in intercropping agroforestry sites than in monoculture sites. Results
from my study suggest that field crop growers can enhance natural enemy populations
and thereby lower pest populations in their crops by using intercropping agroforestry.
Arthropods dwelling in leaf litter were the second main group affected by the
intercropping agroforestry systern. Many members of this ecological group are active
primarily at night and prefer to shelter in humid leaf litter areas during the day. My
resuîts showed that these arthropods tended to congregate in the tree rows of the
intercropped site. This may have k e n a resutt of the elevated amounts of vegetative
matter in the tree rows of the agroforestry field. Larger quantities of vegetative maiter
rnay also explain the higher population of detritivores in the agroforestry field as
compared to the rnonocutture field. An increase in detritivores may improve the
breakdown of crop residues left in a field, and thereby improve the health of the soi1 and
the quality of crop production over the long tem. This may be espeàally advantageous
where no-tillage systems are practiced, since this technique leaves substantial
quantities of vegetative matter on the surface of the field.
lntercropping agroforestry systems have k e n shown to improve upon several
environmental problems with conventional agricuitural systems (USDA, 1997). as well
as conserve biodiversity within the agroecosystem (Newman and Gordon, 1997). The
sustainability of Canadian agriculture depends upon a diversity of organisms that play
important roles in maintaining agriculhiral ecological systems (AAFC, 2001). My results
suggest that intercropping agroforestry can provide improved habitat for a diversity of
arthropods in agroecosystems. Therefote measures should be taken to encourage the
adoption of this agricultural system.
Research lmprovemenb and Recommendations
Like many intercropping agroforestry studies in the temperate region (Stamps
and Linit, 1999a). the design of my study has been compromised by a lack of replicated
agroforestry and monoculture fields. This limits the general applicabiiity of my results to
other intercropping agroforestry fields. The fact that my work is similar to that of other
studies (Stamps et al-, 2000 and Peng et a!., 1993) lends support to its broader
95 implications. A more appropriate design wouid have been to include additional fields, at
a suitable scale and distance from each other (Smith and McSorîey, 2000).
Future studies could produœ a more cornprehensive view of arthropod
communities by simultaneousty employing muttiple trapping methods. One trapping
method that catches primanly ground arthropods (e.g. pan traps or pitfall traps) wuld be
employed in wnjundion with another trapping method that captures primarily aerial
arthropods (e.g. Malaise traps or raised water pan traps). Combining two sampling
techniques may produce a clearer understanding of the ecology both on the ground and
in the air. In my study for instance, using pan traps in conjunction with the Malaise traps
in 1999 cwld have illuminated what was occumng in arthropod groups that are
dependent on leaf litter.
In this study, no significant differenœ was found in the number of pollinators
between the agroforestry and monoculture fields. Other studies shoukl consider
selecting a crop that requires insect pollination, such as clover, squash, strawbemes or
tomatoes. In addition to using an alternative crop in the monoculture and agroforestry
crop alleys, studies should also be conducteci employing tree or shmb species in the
tree rows that require insect pollination, such as rnembers of the genera Prunus or
Amelanchier or tulip-trees (LiMendmn tulipfera L.) .
Arairopod detritivores were found in significantly higher numbers in the
intercropping agroforestry system than in the monoculture system. The higher number
of detritivores could indicate that the use of an agroforestry system would result in
improved breakdown of crop residues. Efforts could be made to compare the activity of
arthropod detritivores in the decomposition of crop residue between intercropping
ag roforestry and monoculture systems.
96 One veiy important avenue of inquiry that requires further study is to compare
intercropping agroforestry and monoculture systems in ternis of pest damage and crop
yield. To date. this has oniy b e n studied by Ogol et al. (1 999). lntercropping
agroforestry should be promoted as a viable alternative to current agricuitural practices
in the temperate region. This cannot occur without sound data to demonstrate both its
short-terrn and long-terni economic value. Growers will need to be convinced that the
benefits of increased crop yield and monetary retum outweigh the costs of rnuitiple crop
systems and potential pests.
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Appendices
Appendix 1 - Number of arthropods in each orderlclass using pan traps during June 1998 from Norway spruce and black walnut sites within the intercroped agroforestry and corn monoculture sites, at the Guelph Agricultural Research Station (n-60).
Arthropod lntercropping agroforestry Monoculture Total % of orders /classes total
sample Walnut Norway
spruce Araneae 65 46 21 132 0.92 Chilopoda Coleoptera Collembola Demapte ra Di plopoda Diptera Hemiptera Homoptera Hymenoptera lsopoda Lepidoptera Odonata Opiliones Orthoptera Psocoptera
NO. of orders 13 13 11 15 No. of classes 2 2 2 2 No. of individuals 5,788 3,958 4,526 14,272 100.00
Appendix 2 - Number of arthropods in each order using Malaise traps during JuneSeptember 1999, from Nomay spruce and black walnut sites within the intercropping agroforestry and corn monoculture study sites, at the Guelph Agricultural Research Station (nt48).
Arthropod lntercropping agroforestry Monoculture Total % of orders total
sample Walnut Norway spruce
Araneae 12 36 38 86 0.27 Coleoptera Collem bola Demiaptera Diptera Hemiptera Homoptera Hymenoptera Lepidoptera Neuroptera Odonata Opiliones Orthoptera Pscocoptera Thysanoptera 17 99 156 272 0.85 No. of orders 14 15 15 15 No.of individuals 9.354 13.-884 8.821 32.059 100.00
Appendix 3 - Number of arthropods in 61 selected families and 2 selected orders that are representing the parasitoid, predator, pollinator, detritivore and herbivore functional guilds; caught in June- September 1999 in the intercropping agroforestry Norway spruce and the corn monoculture study site, at the Guelph Agricultural Research Station (~32).
Arthropod Selected family Guild lntercropping Monoculture Total % of orders and order chssification agroforestry overall
total Araneae Araneae Predatot 36 38 74 0.66 Coleoptera
Collembola
Diptera
Hemiptera
Homoptera
Carabidae C hysomelidae Coccinellidae Entornobryidae Sminthuridae Asilidae Dolichopodidae Pipunculidae Syrphidae Tachinidae Anthocoridae Lygaeidae Miridae Nabidae Red uviidae Ap hidae Cercopidae Cicadellidae Fulgoroidae
Hymenoptera Andrenidae Aphelinidae Apidae Bethylidae Braconidae Ceraphronidae Chalcididae Chrysididae Colletidae Diapriidae Dryinidae Elasmidae Encyrtidae Eucharitidae Eucoilidae
Predator Herbivore Predator Detritivore Det ritivore Predator Predator Parasitoid Predator Parasitoid Predator Herbivore Herbivore Predator Predator Herbivore Herbivore Herbivore Herbivore Pollinator Parasitoid Pollinator Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Pollinator Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid Parasitoid
Appendix 3 cont'd.
Arthropod Selected family Guild Intercropping Monoculture Total % of orders and order classification agroforestry overall
total Hymenoptera Eulophidae Parasitoid 138 65 203 1.81 cont'd . Eupelmidae Parasitoid 16 3 19 0.17
Eurytomidae Parasitoid 36 8 44 0.39 Figitidae Pa rasitoid O 1 1 0.01 Formicidae Predator 69 59 128 1.14 Halictidae Pollinator 60 22 82 0.73 lchneumonidae Parasitoid 217 36 253 2.26 Megachilidae Pollinator 1 O 1 0.01 Megaspilidae Pa rasitoid 9 22 31 0.28 Mutilidae Predator 41 17 58 0.52 Mymaridae Pa rasitoid 257 175 432 3.86 Platygastridae Parasitoid 57 8 65 0.58 Pompilidae Predator 255 92 347 3.10 Proctotrupidae Parasitoid 3 O 3 0.03 Pterornalidae Pa rasitoid 84 34 118 1.05 Scelion idae Parasitoid 376 288 664 5.93 Scoliidae Pa rasitoid 3 25 28 0.25 Sphecidae Predator 71 27 98 0.87 Tenthredinidae Herbivore 1 O 1 0.01 Tiphiidae Parasitoid 2 2 4 0.04 Trichog rammatidae Parasitoid 10 14 24 0.21 Vespidae Predator 32 47 79 0.71
Lepidoptera Noctuidae Herbivore 25 13 38 0.34 Pyralidae Herbivore 8 6 14 0.12
Neuroptera Chrysopidae Predator 58 7 65 0.58 Hemerobiidae Predator 44 12 56 0.50
Opiliones Palpatores Detritivore 38 4 42 0.37 Orthoptera Acrididae Herbivore 12 4 16 0.14 Number families from selected list 60 55 61 Number of orders from selected list 2 2 2 Number of individuals 7,005 4,197 11,20 100
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