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NATIVE BEE VISITATION ON FLORIDA NATIVE WILDFLOWERS

By

KATHARINE D. BUCKLEY

A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2011

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© 2011 Katharine D. Buckley

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To those who knew I was weird and encouraged me to study bugs anyway

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ACKNOWLEDGMENTS

I thank my advisor, Dr. Jamie Ellis, and committee members Drs. Jaret Daniels

and Glenn Hall for all their advice and guidance. I thank Dr. David Jarzen for the

generous gift of the use of his laboratory, supplies and expertise in palynology. I thank

James Colee for helping me with statistics. I also thank my fellow graduate students

Eddie Atkinson, Jason Graham, Pablo Herrera, and Dr. J. Akers Pence as well as

research technicians Jeanette Klopchin, Mark Dykes, Michelle Kelley, Jonnie Dietz and

Ben King for their help and support. I especially thank my family for their love and

encouragement of my desire to study bugs, including letting me keep a tarantula in my

bedroom.

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TABLE OF CONTENTS page

ACKNOWLEDGMENTS.................................................................................................. 4 

LIST OF TABLES............................................................................................................ 7 

LIST OF FIGURES.......................................................................................................... 8 

ABSTRACT ..................................................................................................................... 9 

CHAPTER

1 INTRODUCTION .................................................................................................... 11 

2 MATERIALS AND METHODS ................................................................................ 22 

General Site Information ......................................................................................... 22 Site Preparation and Establishment ................................................................. 23 Site Maintenance.............................................................................................. 24 

Vegetation Survey .................................................................................................. 24 Bee Survey ............................................................................................................. 25 

Primary Bee Surveys........................................................................................ 25 Supplementary Bee Surveys ............................................................................ 26 

Pollen Survey.......................................................................................................... 27 Statistical Analysis .................................................................................................. 29 

3 RESULTS ............................................................................................................... 43 

Overall Bee Attraction to Native Florida Wildflowers............................................... 43 Principle Overlapping Flowers.......................................................................... 43 Spring Time Period........................................................................................... 44 Late Summer/Early Fall Time Period................................................................ 44 Late Fall Time Period ....................................................................................... 45 

Wildflower Visitation by Bee Tribe .......................................................................... 45 Apini (Apidae)................................................................................................... 45 

Spring time period...................................................................................... 45 Augochlorini (Halictidae)................................................................................... 46 Bombini (Apidae).............................................................................................. 46 

Principle overlapping flowers ..................................................................... 46 Late summer/early fall time period ............................................................. 47 

Eucerini (Apidae).............................................................................................. 47 Late fall time period.................................................................................... 47 

Halictini (Halictidae).......................................................................................... 48 Principle overlapping flowers ..................................................................... 48 Spring time period...................................................................................... 48 Late summer/early fall time period ............................................................. 48 

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Late fall time period.................................................................................... 49 Megachilini (Megachilidae) ............................................................................... 49 

Principle overlapping plants ....................................................................... 49 Late summer/early fall time period ............................................................. 49 Late fall time period.................................................................................... 50 

Xylocopini (Apidae) .......................................................................................... 50 Principle overlapping flowers ..................................................................... 50 Late summer/early fall time period ............................................................. 50 

Pollen Washes........................................................................................................ 51 Pollen Wash Means ......................................................................................... 51 Pollen Wash Percentage Likelihood................................................................. 51 Pollen on Bumble Bees .................................................................................... 51 Pollen on Halictus poeyi ................................................................................... 52 

4 DISCUSSION ......................................................................................................... 79 

Benefits of Wildflower Mixes ................................................................................... 79 Native Bee Use of Wildflower Species.................................................................... 79 Developing a Florida Wildflower Mix That Is Used By Native Bees ........................ 81 Study Limitations .................................................................................................... 83 Further Investigations ............................................................................................. 84 Conclusion .............................................................................................................. 88 

LIST OF REFERENCES ............................................................................................... 90 

BIOGRAPHICAL SKETCH............................................................................................ 99 

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LIST OF TABLES

Table page 1-1 Examples of bee forage studies ......................................................................... 21 

2-1 Wildflowers assessed in the study...................................................................... 32 

2-2 Wildflower drought tolerance and months of bloom time .................................... 33 

2-3 Wildflower sources, % pure seed, % germination rate, and ecotype/source of the wildflowers .................................................................................................... 34 

2-4 Grams of wildflower seed per plot ...................................................................... 35 

2-5 Total bees observed and collected ..................................................................... 36 

3-1 Bee visitation of the tested wildflower species.................................................... 53 

3-2 Bee tribe visitation by plant species.................................................................... 54 

3-3 Pollen wash data ................................................................................................ 54 

3-4 Pollen wash percentage likelihoods.................................................................... 54 

3-5 Bumble bee pollen wash means......................................................................... 55 

3-6 Bumble bee pollen wash percentage likelihoods................................................ 55 

3-7 Halictus poeyi pollen wash means...................................................................... 55 

3-8 Halictus poeyi pollen wash percentage likelihoods............................................. 55 

4-1 Bee-plant associations from literature ................................................................ 89 

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LIST OF FIGURES

Figure page 2-1 Map of University of Florida Plant Science Research and Extension Unit near

Citra, Florida ....................................................................................................... 37 

2-2 Plot spacing at the wildflower sites. .................................................................... 38 

2-3 Layout of plots .................................................................................................... 39 

2-4 Grouped Aster-Like pollen at 400x magnification under a light microscope ....... 40 

2-5 Gaillardia pulchella pollen at 400x magnification under a light microscope. ....... 40 

2-6 Helianthus angustifolius pollen at 400x magnification under a light microscope. ........................................................................................................ 41 

2-7 Chamaecrista fasciculata pollen at 400x under a light microscope. ................... 41 

2-8 Monarda punctata pollen at 400x under a light microscope. .............................. 42 

2-9 Example frame locations (in grey) for a vegetation survey ................................. 42 

3-1 Bee visitation (LS-mean number of bees/100 blooms/minute) on the principle six wildflower species ......................................................................................... 56 

3-2 Bee visitation (LS-mean number of bees/100 blooms/minute) on the spring blooming flowers................................................................................................... 1 

3-3 Bee visitation (LS-mean number of bees/100 blooms/minute) on the late summer/early fall blooming flowers .................................................................... 60 

3-5 Apini visitation (LS-mean number of bees/100 blooms/minute).......................... 63 

3-6 Augochlorini overall flower visitation (LS-mean number of bees/100 blooms/minute) ................................................................................................... 65 

3-7 Bombini visitation (LS-mean number of bees/100 blooms/minute)....................... 1 

3-8 Eucerini visitation (LS-mean number of bees/100 blooms/minute) on late fall blooms................................................................................................................ 69 

3-9 Halictini visitation (LS-mean number of bees/100 blooms/minute) ....................... 1 

3-10 Megachilini visitation (LS-mean number of bees/100 blooms/minute).................. 1 

3-11 Xylocopini visitation (LS-mean number of bees/100 blooms/minute) ................... 1 

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science

NATIVE BEE VISITATION ON FLORIDA NATIVE WILDFLOWERS

By

Katharine D. Buckley

August 2011

Chair: James D. Ellis Major: Entomology and Nematology

Declining pollination services in Florida is a cause for concern as several

economically-valuable crops in Florida (blueberries, watermelons and other cucurbits,

citrus, avocados, etc.) require pollination to some degree. Declines in bee populations

associated with pollinating many of these crops have been correlated strongly with the

loss of forage. Consequently, investigators outlining bee conservation programs

recommend improving forage availability for bees using several management schemes,

the most successful of which has been planting seeds from wildflower species known to

attract bees.

The goal of my study was to identify and quantify the attractiveness of several

native Florida wildflower species to native bees for use in native bee conservation. To

that end I surveyed bees on 20 different wildflowers species planted in 5 mixes at 4

different sites to compare bee visitation rates. Ten of the wildflower species

(Chamaecrista fasciculata (Michaux), Coreopsis basalis (A. Dietrich), Coreopsis

lanceolata Linnaeus, Coreopsis leavenworthii Torrey & A. Gray, Gaillardia pulchella

Fougeroux de Bondaroy, Helianthus angustifolius Linnaeus, Monarda punctata

Linnaeus, Rudbeckia hirta Linnaeus, Trifolium incarnatum Linnaeus and Trifolium

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repens (Linnaeus) were significantly more attractive to bees than were the other

species. The attraction of these wildflower species to bees was not uniform and varied

according to time of year, time of day and tribe to which a bee belonged. Overall, G.

pulchella, C. lanceolata, and R. hirta were the most attractive wildflower species to the

bees observed in this project.

The data I collected highlight what native Florida wildflower species are attractive

to bees in general and to some bee tribes specifically. This information can be used by

the general public and/or farmers interested in providing forage for local bee pollinator

species. Combined with extension and outreach materials and programming, the data

provided in this study hopefully will aid the conservation and restoration of native bee

habitat.

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CHAPTER 1 INTRODUCTION

Since The Forgotten Pollinators was published in 1996 (Buchmann & Nabhan

1996) there have been an increasing number of published studies on pollinators. This is

due, in part, to the decline in the number of managed and feral European honey bee

colonies in North America and bumble bee populations and range in North America and

Europe (Corbet et al. 1991; Watanabe 1994; Kearns et al. 1998; Kremen & Ricketts

2000; Steffan-Dewenter 2005; Goulson et al. 2005; Biesmeijer et al. 2006; Grixti et al.

2009; Aizen & Harder 2009). Butterflies also have been the topic of research and media

attention due to declining populations of several widely distributed and well-known

species such as the monarch butterfly and multiple previously common species in

Europe (Van Dyck et al. 2009).

Taken together, these declines have prompted discussion about a pollinator crisis.

While some scientists are skeptical about such a crisis, many remain concerned

(Ghazoul 2005a; Steffan-Dewenter et al. 2005; Ghazoul 2005b; Klein et al. 2007; Kluser

& Peduzzi 2007; National Research Council of the National Academies 2007; Murray et

al. 2009; among others). To address the issue of pollinator decline in North America the

National Research Council investigated the issue, then published a book detailing their

recommendations (National Research Council of the National Academies 2007). The

research presented here touches on a few of their goals for wild pollinator conservation:

“Conservation and restoration of habitat… Basic information on the resource requirements of a wider variety of pollinator

species is needed to improve habitat management…

Encourage the stewards of a wide range of urban and rural areas to adopt pollinator-friendly practices and also to encourage information exchange and outreach…

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Identify and implement practices that promote the availability of diverse commercial and wild pollinators.”

Animal pollinators are estimated to pollinate 90% of all flowering plants

(Buchmann & Nabhan 1996), and 75% of crop plants either need pollinators or produce

better yields when pollinated, accounting for nearly a third of the human diet (Klein et al.

2007). Many animals, including butterflies, moths, flies, beetles, birds, bats, mammals,

and even reptiles are pollinators. Hymenoptera, specifically bees, undisputedly remain

the most efficient pollinators because immature and adult bees feed solely from flowers.

Honey bees are responsible for providing most of the pollination services in

modern agriculture (MacGregor 1976). Unfortunately, honey bees in North America and

globally are under threat from pests, parasites, diseases, pesticides, poor management

practices, low honey prices, and bad publicity due to Africanized honey bees, among

many other stressors (National Research Council of the National Academies 2007).

More bee pollinated crops are grown today than ever before, and honey bee

populations no longer can meet the demand (Allen-Wardell et al. 1998; Aizen & Harder

2009; Aizen et al. 2009).

Fortunately, native bees (non-Apis species of bees) can help supplement honey

bee pollination services. In highly heterogeneous landscapes, native bees can perform

most pollination services (Winfree et al. 2008). Crop fields close to natural areas can be

pollinated almost entirely by native bees in some circumstances (Kremen et al. 2004).

Pollination services provided by honey bees and native bees together can increase fruit

set in several crops (Greenleaf & Kremen 2006). For some crops, like onions and

squash, native bees are more efficient pollinators than honey bees (Parker 1982;

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Canto-Aguilar & Parra-Tabla 2000), and can be managed in high enough numbers to

pollinate the target crops adequately (Shipp et al. 1994).

In many cases however, providing one managed native bee species probably is

not the best solution to the ongoing pollination crisis. A better solution, especially in wild

systems, is the maintenance and propagation of a diversity of pollinators rather than

one or a few species (Klein et al. 2003; Fontaine et al. 2006). High diversity in pollinator

species is best because populations of individual bee species have been shown to vary

considerably from year to year (Williams et al. 2001), making reliance on any one

species risky. Bee communities experience variations not only during the year (different

spring/summer/fall compositions are common), but also year to year with different

dominant species in a multiple year cycle (Williams et al. 2001).

In the interest of increasing or conserving diversity in native bee populations, it is

important to understand bee biology and ecology (Freitas et al. 2009). Bees are very

diverse in their life histories, especially their food and nesting habits. As such, there are

several different issues that need to be addressed in a conservation or pollinator

diversity management plan. These include genetic structure, nest habitat availability,

bee health as affected by external factors such as pesticides and various

pests/pathogens, and food resource availability.

All bees have an unusual genetic structure in common, a structure that makes

them more susceptible to inbreeding: males are haploid and females are diploid (termed

“haplodiploidy”). Because male bees contain only a single copy of DNA while females

have two, males only contribute half as much genetic diversity within the population

compared to that contributed by diploid females. Also, the likelihood of a fertilized egg

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being homozygous at the sex-determining locus increases as a bee population

decreases, thus increasing the probability of a diploid male being produced. Diploid

males cause female mortality directly (as they would have otherwise been female) and

indirectly because their offspring are essentially sterile (Zayed 2009).

Haplodiploidy is not the only unusual genetic structure associated with bees. While

most bees are solitary, many are social. Higher degrees of sociality decrease the

number of reproductively active individuals in the total population as numbers of non-

reproductive workers increase. Fewer reproductives lead to lower genetic diversity

within the population, thus increasing the chances of inbreeding depression (Zayed

2009). In bee conservation and management programs, genetic diversity is an indicator

of healthy bee populations.

The problem with controlling bee genetics is that to date genetic testing cannot

replace a pedigree for predicting inbreeding (Grueber et al. 2011). Since many bee

species of conservation importance often have cryptic nesting habits as well as

relatively unknown life histories, especially mating systems (Zayed 2009), pedigrees for

wild bees currently are very difficult to determine.

Because of the difficulties associated with monitoring genetics, the monitoring of

nest sites can be done to give some indication of the health of bee populations (Frankie

et al. 1998). Creating suitable nesting habitat is one of the three most common methods

currently used in bee conservation and management programs (the other two being

pesticide use reduction and increasing bee forage plants). Several native bee species

are managed successfully for crop pollination by providing suitable nesting habitat.

Managed native species include the blue orchard bee (Osmia lignaria), the alkali bee

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(Nomia melanderi), the alfalfa leafcutter bee (not technically native, but a notable

managed solitary species) (Megachile rotundata), and several bumble bee species

(Bombus spp.) (Johansen et al. 1978; Peterson et al. 1992; Bosch & Kemp 2001;

Velthuis & van Doorn 2006). These bees all are managed by inducing populations of the

bees to nest where pollination services are needed.

Many other bee species can be trap-nested in bamboo, different sized straws, and

holes drilled into wood (Krombein 1967). However, most bee species nest in the ground

(Michener 2007) so other management schemes are necessary. One of the most

recommended methods of encouraging ground nesting bees to nest in an area is to

keep the ground as undisturbed as possible by limiting tilling (Vaughan et al. 2004).

Furthermore, one can create soil mounds or banks in a bee’s preferred nesting soil type

since sites with bare soil are encouraged (Vaughan et al. 2004). Keeping a record of

where bees are nesting from year to year or how many bees are using trap-nest sites

can give one a reasonable estimation of bee populations in an area.

Bee health is another factor one must consider when developing a conservation or

pollinator diversity program. Bee health is affected by many external factors (weather,

climate change, pesticides, poor nutrition, predators and parasites, etc.) perhaps the

most damaging of which are pesticides. Many common insecticides are known to affect

native bee populations (Johansen 1977; Kevan 1999; Desneux et al. 2007). Even at

sub-lethal levels, some insecticides have been shown to cause navigating problems in

adult bees, leading to higher forager mortality, decreased food availability in social

colonies and lower fecundity among solitary bees whose level of reproduction is limited

by the amount of food for which they can forage in their lifetimes (Desneux et al. 2007;

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Winfree 2010). Other pesticides, including some common fungicides, have been

associated with direct mortality in honey bees (Desneux et al. 2007), which typically

serve as a surrogate for native bees in 50% lethal dose (LD50) tests required by the EPA

before a pesticide can be registered (OECD 2010). To a lesser extent (largely for

research purposes) bumble bees, alfalfa leafcutter bees and alkali bees also have been

used in insecticide testing (Johansen 1977; Drescher & Geusen-Pfister 1991;

Thompson & Hunt 1999). Johansen (1977) showed that all species tested displayed a

different LD50 to the same chemicals, thus calling into question the idea that honey bees

can be used as a model for the effects of pesticides on other pollinator species and

pollinator communities (Thomson & Hunt 1999; Barmaz et al. 2010).

Herbicides and weed management also may affect bee populations negatively

(Johansen 1977). Mowing weedy roadsides causes a noticeable decline in bee

populations because the weeds’ flowers provide forage when nearby crops are no

longer flowering (Benedek 1996). Similarly, herbicide use also can reduce available

forage for pollinators in an area. Since many solitary bees are constrained by the

distance they can fly and have foraging seasons that outlast a given crops’ flowering

period, bee populations near crop fields where intensive weed management is practiced

often suffer. From the standpoint of pesticides (herbicides included), conservation and

management practices for native bees include reduced pesticide use as an important

component (Vaughan et al. 2004).

Though genetic structure, nest habitat availability and bee health are important

considerations in native bee conservation schemes, the availability of food resources

(i.e. nectar and pollen) is of major importance, and, therefore, the subject of my thesis.

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Bees are flower obligates, i.e. bees acquire their food exclusively from flowers. Adult

bees use nectar as their carbohydrate source and actively gather pollen which is fed to

bee larva as their protein source (Michener 2007). Some bees also collect volatile floral

oils, which may be used as mating pheromones (Eltz et al. 1999). This mutualism

between flowers and bees has led to the theory that the abundance and diversity of

bees in an area can be estimated with a combination of pan traps near flowers as well

as active netting from flowers (LeBuhn et al. 2003, Matteson et al. 2008). Due to bees’

often cryptic nesting habitat, collecting from flowers is usually the most reliable method

of monitoring bee populations (Roulston et al. 2007).

Bee dependence on flowers for food also has led to the theory that planting

flowers that bees actively utilize could improve their populations. Declines in bee

populations have been correlated strongly with the loss of forage, especially in bumble

bees (Benedek 1996; Goulson & Darvill 2004; Biesmeijer et al. 2006; Carvell et al.

2006; Kleijn & Raemakers 2008; Decourtye 2010). These declines have been especially

prevalent with the current tendency towards agricultural intensification (Kim et al. 2006).

Therefore a major tool used in bee conservation programs has been increasing forage

for bees using several different management schemes, the most successful of which

has been sowing plant mixes known to attract bees (Carvell et al. 2004; Pywell et al.

2006; Carvell et al. 2007; Potts et al. 2009). It has not been conclusively demonstrated

that planting wildflowers increases bee populations and diversity. It has, however, been

shown that bee visitations and diversity within a crop strongly increases with proximity

to ‘natural habitat’, although actual crop production showed only a weak increase

(Ricketts et al. 2008). Increasing suitable habitat in agricultural areas has been shown

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to increase population of several other groups, so providing flowers for bees would likely

increase their numbers as well (Goulson 2003). The subsequent problem that arises lies

in determining which flowering plants are beneficial to various local bee communities in

attempting to restore this ‘natural habitat’.

Researchers in Europe, and especially Great Britain, have pioneered most of the

studies on bee plant preference (Carvell et al. 2004; Pywell et al. 2005; Pywell et al.

2006; Carvell et al. 2007; Potts et al. 2009). The majority of these studies include bees

and plants that are not native to North America and in some cases are considered

invasive weeds (Winfree 2010). To date, the only studies of native bee forage

preference in the United States have been in Washington (Patien et al. 1993), California

(Vaughn et al. 2004; Frankie et al. 2005), Michigan (Tuell et al. 2008), and New Jersey

(Williams et al. 2009).

Many of these studies, including those in Europe, include information regarding

the bees surveyed on specific plants or in a specific area without considering the

amount and density of available blooms (Winfree 2010). The problem with this strategy

is that it tests bees’ use of flowers, but not their actual preference for certain flowers

(Winfree 2010). A more attractive but less abundant plant may have fewer visits than a

less attractive but highly abundant plant. Consequently, studies that do not include

vegetation information such as survey data or standardized plots of plants cannot

confirm bee preference of a particular flower, rather only bee use of that flower.

There is a solution to this to this dilemma. Plant surveys should be conducted

when determining bee preference for a given plant because the information can be used

to estimate the relative abundance of flowers on which the bees are being found

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(LeBuhn et al. 2003). There are a few examples of investigators who have used this

method (Johnson 1980; Kells et al. 2001; Williams 2005; Williams et al. 2010). Another

technique that can be used to estimate bee preference for a given plant is to grow

different plant species at standard densities and conduct bee surveys on these

standardized plots (Tuell et al. 2008).

While Patien et al. (1993), Vaughn et al. (2004), Frankie et al. (2005), Tuell et al.

(2008), and Williams et al. (2009) did survey a large number of wildflowers native to

North America, many of the plants and/or bees surveyed were not native to central

Florida. For concerned Floridians this is a problem because wildflowers native to Florida

may support native pollinators better than would non-native plants (Frankie et al. 2005).

Native plants are less likely to behave invasively, less likely to support invasive pest

insects, and more likely to be adapted to local conditions (Rieff 2011). Consequently

these beneficial qualities will make the general public more likely to use native plants,

especially since they likely will require less fertilizer, pesticides and watering than non-

native plants (Florida’s Water Management Districts 2009).

Though certain plants are known to be highly attractive to bees, different plants

bloom at different times throughout the year. Furthermore, local bee communities

change throughout the year (although eusocial species often are found year round,

which is why they benefit most from year round forage). As such, anyone developing a

native seed mix that would include seeds of plants attractive to a wide variety of bee

pollinators needs to consider the bloom period of tested plants as well as the

abundance of bees seasonally.

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Despite multiple studies on the composition of the bee community in Florida

(Graenicher 1930; Pascarella et al. 1999; Deyrup et al. 2002; Hall & Ascher 2010), and

publicly accessible keys to Florida bees with flower associations (Pascarella 2008;

Ascher & Pickering 2010), no comparative study of native bee flower preference has

been conducted in Florida, or anywhere else in the south-eastern United States.

Declining pollination services in Florida is cause for concern, as several economically-

valuable crops in Florida (blueberries, watermelons and other cucurbits, citrus,

avocados, etc.) require pollination to some degree (MacGregor 1976). Conservation in

general is also a concern. For example, Florida’s main ecosystem, pine flatwoods, has

a diverse plant understory including many wildflower species which require insect

pollination to reproduce (Myers & Ewel 1990; Whitney et al. 2004). Therefore, the

conservation of native Florida bees, which likely are a major pollinating group in this

ecosystem, should remain a high priority.

The goal of the current study is to identify and quantify the attractiveness of

several native Florida wildflower species to native bees. I hypothesize that different

common Florida bee species will exhibit varied preferences for a host of wildflower

species. Further, I expect bee preference for certain plants to change during the year. I

hope that this information will contribute to the development of a pollinator seed mixture

that would support the greatest number and diversity of bees throughout the year. Such

a mix potentially would provide year-round forage for native bees in otherwise florally

depauperate areas such as agriculture-intense regions. My long term goal is that the

information I present herein could be used to develop conservation practices for native

bees, thus protecting the pollination services they provide.

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Table 1-1. Examples of bee forage studies

Location Study Reference California and New Jersey

Analyzed native versus non-native bee forage plants – bees did not prefer non-native and non-native abundance did not affect bee diversity

Williams et al. 2010

California Tested attractiveness of common ornamental plants to different bee groups for bee population survey purposes in urban areas

Frankie et al. 2009

UK Tested seven grassland management strategies for bumble bee response – responded best to sown flowers

Potts et al. 2009

Michigan 43 native perennials tested for bee preference for use in bee conservation

Tuell et al. 2008

New Jersey and Pennsylvania

Bee visitation rates across organic and conventional farms - suggest landscape effects important and bee conservation best focused on intensively farmed areas for best effects

Winfree et al. 2008

UK

Compared Environmental Stewardship schemes for bumble bee use - recommend legume flower mix with greater seasonal bloom diversity and/or diverse perennial forage plants

Carvell et al. 2007

UK Comparison of annual and perennial mixes - different bee species preferred different mixes

Carvell et al. 2006

UK Comparison of seed mixes on bumble bee diversity and abundance - wildflower and forage plant mixes performed best

Pywell et al. 2006

UK Four management strategies for field margins compared for bumble bees - wildflower seed mix significantly better

Pywell et al. 2005

Finland

Field margin effects on bumble bee diversity - flowers over grass, most important are a few flower species' abundance during bumble bee reproduction period

Bäckman & Tiainen 2002

UK Six flowers planted at various times and ratios, evaluated for different pollinating insect preferences

Carreck & Williams 2002

UK Five treatments of field margins indicate sown mixes better than natural regeneration

Meek et al. 2002

UK Bees prefer natural regeneration over cropped field margins

Kells et al. 2001

Washington 21 herbaceous bee forage plants evaluated for planting near cranberry farms - honey bee and bumble bee preferences differ

Patien et al. 1993

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CHAPTER 2 MATERIALS AND METHODS

General Site Information

Five different wildflower mixes were planted (Table 2-1) at four sites at the

University of Florida Plant Science Research and Extension Unit (PSREU) near Citra,

Florida (N29°24'36.28" W82°10'11.90"). There were six plots at every site: (1) control,

(2) basic annual flower mix, (3) basic perennial flower mix, (4) diverse annual flower

mix, (5) diverse perennial flower mix and (6) a mixture of annual and perennial flowers.

The wildflower species were selected based on potential attractiveness to pollinators,

their status as regionally native or naturalized, seed availability, low cost, similar

management, and representing a diversity of bloom times (spring/summer/fall) (Table 2-

2, Table 2-3). Eighteen species of native Florida wildflowers were selected along with

three naturalized wildflowers: Phlox drummondii Hooker, Trifolium incarnatum Linnaeus

and T. repens Linnaeus (Table 2-1). Coreopsis basalis (A. Dietrich), C. lanceolata

Linnaeus, C. tinctoria Nuttall, Gaillardia pulchella Fougeroux de Bondaroy, Monarda

punctata Linnaeus, Helianthus angustifolius Linnaeus, P. drummondii and Rudbeckia

hirta Linnaeus were also specifically chosen because they are commonly planted along

Florida roadsides as part of the Florida Department of Transportation’s wildflower

program. A few of these species either never grew or produced too few flowers to

attract bees significantly.

The four sites at the PSREU were > 1000 m from one another (Figure 2-1). All

sites were prepared during the fall of 2009. Each site was ~75 × 21 m, containing the

six plots which were 15 × 3 meters each and spaced 10 m from one another (Figure 2-

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2). The type of wildflower seed mix planted was randomized among the plots within a

site.

1) Site 1 - N29˚24.621' W082˚10.828' (Figure 2-3a)

2) Site 2 - N29˚24.163' W082˚10.124' (Figure 2-3b)

3) Site 3 - N29˚24.610' W082˚08.360' (Figure 2-3c)

4) Site 4 - N29˚24.227' W082˚08.912' (Figure 2-3d).

Site Preparation and Establishment

I followed methods suggested by Florida wildflower experts (Janet Grabowski,

USDA, NRCS Florida state office; M.J. Williams, USDA, NRCS Florida state office; and

Jeff Norcini, Oecohort, LLC) for planting the 5 seed mixes at each site (Norcini &

Aldritch 2004). Site preparation began September 15, 2009. Plots were measured and

laid out at all sites following which the plots were treated with glyphosate

(TouchdownTM) at 3 qt/acre mixed with Induce® pH, a non-ionic surfactant, at 1 pt/acre.

After seven days, the Bahia grass in the plots was cut with a Hiniker 5700 Flail-chopper

which cuts the grass to 5-8 cm tall and vacuums up the cuttings. On 3 November, the

plots were treated with glyphosate again. Later that week, herbicide resistant

perennials, including Mexican Tea (Chenopodium ambrosioides Linnaeus), Hairy Indigo

(Indigofera hirsuta Linnaeus), Benghal Dayflower (Commelina benghalensis Linnaeus)

and Nutsedge (Cyperus spp.), were removed with shovels. On 17 November, the plots

were burned to remove the remaining dead thatch. Although the thatch burned well, the

hard roots of the Bahia grass in many places did not, forming thick mats in some places.

It was determined that a Lely Rod Weeder (Lely USA, Pella, IA) would be able to break

up the mats while disturbing the soil as little as possible. Several passes from different

directions were necessary to break up the root masses.

24

Seeds were mixed beforehand at densities per acre based on manufacturer’s

recommendations (Table 2-4). Chamaecrista fasciculata (Michaux) and Baptisia alba

(Linnaeus) were scarified in tumblers with sandpaper to improve the chances of

germination. All seeds were weighed carefully and individually bagged in preparation for

planting. On 8 December, sites once again were raked with the Lely Rod Weeder and

rolled with a 16 foot cylindrical roller. The seeds were mixed with 19L sand and spread

over their respective plots using Scotts Pro Turf Professional SS2 Drop Spreaders (The

Scotts Company LLC, Marysville, OH). Plots then were pressed with the roller in an

effort to keep the seeds from blowing away. Sites were irrigated with 1.25 to 2.5 cm of

water, once a week when < 0.6 cm of rain fell. Irrigation aided in seedling establishment.

Site Maintenance

Little maintenance was necessary once the wildflowers were established. Wild

radishes (Raphanus raphanistrum Linnaeus) were weeded from Site 1 early in the

season when they were growing in high densities. On 10 August, I removed large

perennial weeds (most notably Hairy Indigo (Indigofera hirsuta) which resembled small

trees) from all plots except the control. A few weeks later, it was determined that

Partridge Pea (Chamaecrista fasciculata) had established too densely and was shading

out the other wildflower species in the annual mixes. Consequently, the Partridge Pea

was thinned by roughly 25%.

Vegetation Survey

Vegetation surveys were conducted the day prior to the beginning of the intensive

bee surveys, except for the first vegetation survey which was conducted the week prior

to the first bee survey due to the length of time it took to perform. During the first

vegetation survey, all plant stems, percent vegetation cover, and number of blooms in

25

10, 1 × ½ m frames were noted for each plot at all sites. The frames were placed

randomly in 10 different areas delineated within a plot (Figure 2-9). This level of

replication was necessary because of the performance of varying plant species from

one side of a plot to the other, this likely due to different amounts of watering or a slight

slope throughout the plot causing differences in soil moisture and nutrients (Elzinga et

al. 1998). During subsequent surveys, only the number of blooms and percent bloom

coverage were noted.

Bee Survey

Primary Bee Surveys

The primary bee surveys were conducted at all sites every third week. Nine

surveys were conducted from 11 May - 4 November 2010. Each survey lasted two days,

with two teams consisting of an observer and a recorder responsible for one site both

days. The surveys involved observing bees on each plot at each site for 10 minutes,

followed by 10 minutes of collecting bees from the plot. This was done once in the

morning and once in the early afternoon every sampling day. For each plot sampling,

the recorder would record all information for the observer, leaving the observer’s hands

and eyes free. The recorder also was responsible for noting the weather conditions, and

recording time, date, location, and sampling data for each survey (Figure 2-7).

During the observation period, the observer would walk down the sides of the plot

and tell the recorder which bees they saw (Table 2-5) and which flowers the bees were

visiting. The recorder would write down the flower and bee type per the observer’s

comments. The observer walked the perimeter of the plot twice during the 10 minute

observation period. During the first trip around the plot, the observer would identify

every new bee sighted. During the second trip, he/she only noted novel bees (species

26

not seen during the first trip) or increases in the frequency of a previously observed bee

species. For example, if 15 Bombus impatiens were seen during the first trip and 17

during the second, the greater of the two numbers was used.

For each ten minute collection period, the observer randomly chose a side of the

plot from which to collect in the morning, which was alternated during the afternoon

sampling period. This was due to the possibility of some of the flowers becoming

damaged from the action of netting bees in the morning, so sides were alternated to

avoid bias. Bees were captured using standard 45 cm diameter butterfly nets and were

placed immediately into kill jars prepared with cyanide. After the collection period was

over, the collected bees were placed into labeled vials and frozen in preparation for

subsequent pinning and identification. At the beginning of the season, most bees seen

on the wildflowers were captured as reference specimens. After several samplings, I

discovered that many of the bees being captured were one species, Halictus poeyi,

which could easily be sight identified. After that, only one specimen of H. poeyi was

caught during each sampling period, although samples of all other bees were collected

for identification and for bee community composition determination (Table 2-5).

Supplementary Bee Surveys

Supplementary bee surveys were conducted every other week except those

weeks on which the primary bee surveys fell. These surveys were conducted over all

sites in one day by a team of two individuals. Unlike the primary bee surveys, the

supplementary surveys were conducted by surveying each plant species for visiting

bees for a total of 10 minutes at every site across all plots.

Similar to the primary surveys, the team consisted of a recorder and an observer.

For ten minutes the observer would walk around all plots within a site containing a

27

targeted plant species. Any bees seen on that plant during the ten minute observation

period were recorded (Table 2-5). During this time, voucher specimens of unknown

species were captured (pinned and identified) (Table 2-5) as were bees seen carrying

large pollen loads (saved for the pollen survey).

Bee species were identified using Michener (1994) and Pascarella (2010). All

other insects were identified to family using Johnson & Triplehorn (2004). Voucher

specimens are maintained at the Honey Bee Research and Extension Lab from both

surveys.

Pollen Survey

To determine pollen use by the bees, I collected and pressed samples from each

blooming wildflower species throughout the study. At the end of the study, I created

reference slides of the pollen for each species in order to create a pollen reference

collection. To do this, I used the preparation technique for modern pollen and spores as

outlined in Jarzen 2008. Permanent reference slides were created using the glycerine

jelly techniques also outlined in Jarzen 2008.

The pollen preparation method was as follows:

The reference material (a single flower) was placed in 15 cc centrifuge tubes and half filled with 5% KOH.

The tubes were placed in a hot water bath at about 90°C for two to three minutes and then removed.

The tube’s contents were stirred with a glass rod and then poured through a fine meshed plastic screen into a clean 15 cc centrifuge tube.

The 15 cc tubes were centrifuged at 1500 rpm for two to three minutes, decanted, and the contents in the tube were washed twice with distilled water and once with glacial acetic acid. To conduct a wash (from this point forward), the washing liquid was poured into the tube until the total volume reached approximately a centimeter from the top, unless otherwise specified. The tubes then were centrifuged and decanted in preparation for the next wash.

28

Once the washes were complete, the tubes were half filled with acetolysis mixture (one part concentrated sulfuric acid to nine parts acetic anhydride) and placed in a hot water bath for 3-5 minutes.

The tubes were removed and allowed to cool before centrifuging and decanting into a large beaker under running water.

The contents of the tube were washed once with glacial acetic acid, twice with distilled water, and once with a 1:1 mixture of glycerin and distilled water. After decanting, the tubes were allowed to drain upside down overnight.

The next day, a small cube of glycerine jelly was placed in the bottom of the tube and the tube placed in hot water bath until the glycerine jelly was completely melted. The resulting product was stirred thoroughly.

One drop of the glycerine mix was placed onto a pre-cleaned microscope slide and a cover slide was pressed gently on the drop using toothpicks. The remaining glycerine mix was stored in individual vials at room temperature.

The slides were allowed to air dry for at least 24 hours before they were sealed using Sally Hansen “Hard as Nails”® clear nail polish (Coty LLC, Uniondale, NY).

Bees visibly carrying pollen were captured in individual vials during the

supplementary sampling for pollen collection analysis. They were stored in individual

vials in a freezer until identification and pollen washing could be performed.

The bees were washed according to the pollen washing procedure outlined by

Ellis and Delaplane (2008). A stock solution of 45 parts by volume 70% ethyl alcohol, 3

parts by volume liquid soap, and 2 parts by volume basic fuchsin at 5% concentration

was prepared. This was added to the vials containing individual bees in quantities as

follows: small bees (i.e., Lasioglossum spp.) = 0.125 ml; medium bees (i.e., large

Halictus poeyi to Melissodes communis) = 0.250 ml; and large bees (i.e., Xylocopa and

Bombus spp.) = 0.500 ml. After the addition of the stock solution, the vials were closed

and vortexed for 1.5 minutes.

As the pollen was not analyzed immediately following the addition of stock

solution, the vials always were stirred using a vortex for at least 15 seconds prior to

29

analysis. To determine the volume and type of pollen that individual bees were carrying,

a drop of the pollen suspension was loaded into a Bright-Line® Reichert hemacytometer

(manufacturer, city, state). All pollen grains within the center square millimeter were

identified, counted and recorded. Four samples were counted per bee. The four

samples were averaged and, following the hemacytometer’s instructions, (1) multiplied

by 10,000, (2) then multiplied by the milliliters of stock solution added to the bee’s vial.

The resulting number is the approximate pollen load of that bee. Pollen was identified

(Kapp et al. 2000) to one of six different categories: Grouped Aster-like (Coreopsis spp.

and Rudbeckia hirta) (Figure 2-4), Gaillardia pulchella (Figure 2-5), Helianthus

angustifolius (Figure 2-6), Chamaecrista fasciculata (Figure 2-7), Monarda punctata

(Figure 2-8) and Unknown.

These groups of pollen were relatively easy to distinguish from one another. Most

were very different shapes. For example, M. punctata pollen was spheroid with six

furrows, while C. fasciculata pollen was a flattened oblong shape with two furrows on

each side. All Asteraceae pollen in this study was a spiky ball, which is very typical of

the family. Some were indistinguishable to me, hence the Aster-Like group. However, H.

angustifolius had a significantly larger pollen grain size than the other Asteraceae in the

study, and G. pulchella had a very distinctive two part spike. For comparative purposes,

all included figures of pollen were photographed at exactly the same settings and

magnification (Figure 2-4 to 2-8).

Statistical Analysis

To facilitate data analysis, the bee survey data was paired with the vegetation

survey data to create the standard unit of measure: # bees/100 blooms/minute (number

of bees visiting 100 blooms of a particular wildflower species during one minute) which

30

was the dependent variable. The overall bee survey data (grouping all bees together

independent of bee species) were analyzed using a generalized linear model (GLM)

procedure with an exponential distribution (SAS Institute, 2010), recognizing plant

species, the estimated number of blooms for that plant species, and the overall number

of species in bloom in the plot as the independent variables. Furthermore, the GLM

procedure was run by morning and afternoon samplings as it had been noted previously

during sampling that time may affect bee species use of various wildflowers. The overall

bee survey data then was analyzed by three time periods; spring (May though the first

week of June), late summer/early fall (end of July to mid-October), late fall (beginning of

October to early November) and a fourth period when the six longest blooming and

most attractive plant species overlapped completely in bloom. These species included

Chamaecrista fasciculata, Coreopsis basalis, Coreopsis lanceolata, Coreopsis

leavenworthii, Gaillardia pulchella, and Rudbeckia hirta. For each time period, only

flowers that bloomed throughout the entire period were included in the analysis.

Furthermore, I determined which wildflowers were used most by each bee tribe,

the lowest taxonomic level that could be sight identified reasonably during monitoring.

Where possible (i.e. when enough data were collected), bee tribe use of the various

wildflower species was analyzed by time period using the GLM procedure already

described (SAS Institute, 2010).

For the pollen data, the means and standard error are reported; along with the

percent likelihood that a bee caught on a species of wildflower will be carrying pollen

from that flower species. The two groups most captured (H. poeyi and Bombus spp.)

31

were analyzed separately and their means, standard errors, and percent likelihood that

they carried the pollen from the flower which they were captured were determined.

32

Table 2-1. Wildflowers assessed in the study Scientific Name Common Name Family Sig.Asclepias tuberosa Linnaeus Butterfly Milkweed Asclepiadaceae No Baptisia alba (Linnaeus) White Indigo Fabaceae No Chamaecrista fasciculata (Michaux)

Partridge Pea Fabaceae Yes

Coreopsis basalis (A. Dietrich) Dye Flower Asteraceae YesCoreopsis lanceolata Linnaeus Lanceleaf Coreopsis Asteraceae YesCoreopsis leavenworthii Torrey & A. Gray

Leavenworth's Coreopsis Asteraceae Yes

Coreopsis tinctoria Nuttall Golden Tickseed Asteraceae YesEryngium yuccifolium Michaux Rattlesnake Master Apiaceae No Gaillardia pulchella Fougeroux de Bondaroy

Blanketflower Asteraceae Yes

Helianthus angustifolius Linnaeus

Narrow-leaved Sunflower Asteraceae Yes

Ipomopsis rubra (Linnaeus) Standing Cypress Polemoniaceae No Liatris spicata (Linnaeus) Spiked Gayfeather Asteraceae No Monarda punctata Linnaeus Spotted Bee Balm Lamiaceae YesPhlox drummondii Hooker Drummond Phlox Polemoniaceae No Rudbeckia hirta Linnaeus Black Eyed Susan Asteraceae YesSalvia coccinea Buc’hoz ex Etlinger

Tropical Sage Lamiaceae No

Solidago fistulosa Miller Pinebarren Goldenrod Asteraceae No Trifolium incarnatum Linnaeus Crimson Clover Fabaceae No Trifolium repens Linnaeus Osceola Clover Fabaceae No Vernonia gigantea (Walter) Giant Ironweed Asteraceae No Osceola Clover is a cultivar of White Dutch Clover. “Sig.” implies either that a flower could not be used in the analysis (no = the species either did not produce any blooms or did not attract enough bees to be used in statistical analysis) or that it could be used in the analysis (yes).

33

Table 2-2. Wildflower drought tolerance and months of bloom time Bloom Time

Plant Drought

Tolerance J F M A M J J A S O N DAsclepias tuberosa High X X X X X Baptisia alba High X X X Chamaecrista fasciculata Medium X X X X X Coreopsis basalis High X X X X Coreopsis lanceolata High X X X X X X Coreopsis leavenworthii Low X X X X X X X X Coreopsis tinctoria Low X X X Eryngium yuccifolium Low X X X X Gaillardia pulchella High X X X X X X X XHelianthus angustifolius Low X X Ipomopsis rubra High X X X Liatris spicata Low X X X Monarda punctata High X X X X Phlox drummondii High X X X X Rudbeckia hirta High X X X X X X X Salvia coccinea Medium X X X X X X X X X X Solidago fistulosa High X X Trifolium incarnatum Low X X X Trifolium repens Medium X X Vernonia gigantea Medium X X X

34

Table 2-3. Wildflower sources, % pure seed, % germination rate, and ecotype/source of the wildflowers

Scientific Name Wildflower Source % Pure Seed

Germination Rate

Ecotype/Source

Asclepias tuberosa ERNST Seeds 99.61% 80% CA Baptisia alba Florida Wildflower

Cooperative 98% 80% FL

Chamaecrista fasciculata ERNST Seeds 99.22% 21% FL Coreopsis basalis Florida Wildflower

Cooperative 98% 65% FL

Coreopsis lanceolata Florida Wildflower Cooperative

95% 65% FL

Coreopsis leavenworthii Florida Wildflower Cooperative

85% 55% FL

Coreopsis tinctoria ERNST Seeds 93.21% 62% NC Eryngium yuccifolium ERNST Seeds 79.42% 1% FL Gaillardia pulchella Florida Wildflower

Cooperative 89% 85% FL

Helianthus angustifolius Florida Wildflower Cooperative

95% 55% FL

Ipomopsis rubra Florida Wildflower Cooperative

95% 75% FL

Liatris spicata ERNST Seeds 87.09% 40% FL Monarda punctata ERNST Seeds 99.89% 87% SC Phlox drummondii Florida Wildflower

Cooperative 99% 65% FL

Rudbeckia hirta ERNST Seeds 99.80% 93% NC Salvia coccinea Wildseed Farms 99.97% 91% TX Solidago fistulosa ERNST Seeds 14.66% 14% FL Trifolium incarnatum Adams-Briscoe Seed

Company 98% 80% GA

Trifolium repens Adams-Briscoe Seed Company

99.65% 90% GA

Vernonia gigantea Florida Wildflower Cooperative

85% 45% FL

35

Table 2-4. Grams of wildflower seed per plot Plant AB AD PB PD Combo Asclepias tuberosa 18.00g Baptisia alba 4.01g 10.04g 4.62g Chamaecrista fasciculata 80.70g 40g 70.20g Coreopsis basalis 5.04g 2.52g 2.22g Coreopsis lanceolata 7.57g Coreopsis leavenworthii 1.26g 0.76g Coreopsis tinctoria 0.78g Eryngium yuccifolium 10.04g Gaillardia pulchella 12.60g 6.05g 11.50g Helianthus angustifolius 14.13g Ipomopsis rubra 4.88g Liatris spicata 6.38g 1.79g 1.79g Monarda punctata 0.50g Phlox drummondii 5.55g Rudbeckia hirta 4.70g 2.90g 1.74g Salvia coccinea 7.01g 5.04g Solidago fistulosa 5.04g 5.04g 5.04g Trifolium incarnatum 100.90g 100.90g Trifolium repens 15.20g 15.10g 15.20g Vernonia gigantea 5.42g 0.72g 2.17g

Mix abbreviations refer to Perennial Basic (PB), Perennial Diverse (PD), Annual Basic (AB), Annual Diverse (AD), and Combination of Annual and Perennial (Combo) wildflower mixes.

36

Table 2-5. Total bees observed and collected

Tribe Obs. Genus Obs. Coll. Species Obs. CollAnthidiini 1 Anthidiellum 1 1 Anthidiellum (Loyolanthidium) perplexum (Smith) 1 1Apini 87 Apis 87 9 Apis mellifera Linnaeus 87 9Augochlorini 17 Augochlorella 2 Augochlorella aurata (Smith) 2

Augochloropsis 2 Augochloropsis anonyma (Cockerell) 2Bombini 694 Bombus 694 60 Bombus (Pyrobombus) bimaculatus Cresson 2

Bombus (Cullumanobombus) fraternus (Smith) 19 1Bombus (Pyrobombus) impatiens Cresson 191 35Bombus (Thoracobombus) pensylvanicus (DeGeer) 130 22

Colletini 3 Colletes 3 3 Colletes thysanelle Mitchell 3 3Epeolini Epeolus 3 Epeolus glabratus Cresson 1

Epeolus pusillus Cresson 2Triepeolus 9 Triepeolus lunatus (Say) 7

Triepeolus rufithorax Graenicher 2Eucerini 163 Melissodes 16 Melissodes communis Cresson 16

Svastra 27 Svastra aegis (LaBerge) 2 26Svastra petulca (Cresson) 1

Halictini 3437 Agapostemon 137 18 Agapostemon splendens (Lepeletier) 137 18Halictus 3278 648 Halictus (Odontalictus) poeyi Lepeletier 3278 648Lasioglossum 22 10 Lasioglossum (Dialictus) nymphale (Smith) 1

Lasioglossum (Dialictus) pectorale (Smith) 1Lasioglossum (Dialictus) puteulanum Gibbs 1

Sphecodes 2 Sphecodes heraclei Robertson 2Megachilini 230 Coelioxys 1 2

Megachile 229 59 Megachile (Acentron) albitarsis Cresson 4 33Megachile (Litomegachile) brevis Say 2Megachile (Litomegachile) mendica Cresson 16Megachile (Argyropile) parallela Smith 1Megachile (Leptorachis) petulans Cresson 2Megachile (Sayapis) policaris Say 1Megachile (Litomegachile) texana Cresson 4

Nomadini Nomada 1 Nomada fervida Smith 1Nomiinae 1 Dieunomia 1 1 Dieunomia heteropoda (Say) 1 1Xylocopini 121 Xylocopa 121 6 Xylocopa (Schonnherria) micans Lepeletier 43 5

Xylocopa (Xylocopoides) virginica (Linnaeus) 5 1 Abbreviations refer to Observed (Obs.) and Collected & Identified (Coll.) bees. For some bee tribes, the identified bee species in the last Obs. column are only a subset of the observed bees in that tribe. Bees in bold were those included in the statistical analysis .

37

Figure 2-1. Map of University of Florida Plant Science Research and Extension Unit near Citra, Florida. The four sites are labeled and separated by >1000 m. Permission courtesy of Daniel L. Colvin.

  1 

1 4

3

2

1 2 3 4

38

Figure 2-2. Plot spacing at the wildflower sites.

15m

22m

68m

10m 75m

3m

39

Figure 2-3. Layout of plots within: A) Site 1, B) Site 2, C) Site 3, D) Site 4. Note direction north. Abbreviations marking wildflower mixes in plots are as follows: AB = Annual Basic, AD = Annual Diverse, Combo = Combination of Annual and Perennial mixes, PB = Perennial Basic, PD = Perennial Diverse. Control is the control plot in which no seeds were sown.

N

PD

Combo

PB

AD

AB

Control

N

AD

Combo

Control

PD

AB

PB

N

Combo

PB

AD

PD

AB

Control

N

AD

PD

PB

AB

Combo

Control

A B D C

40

Figure 2-4. Grouped Aster-Like pollen at 400x magnification under a light microscope. Examples: A) Coreopsis lanceolata, B) Coreopsis leavenworthii, C) Rudbeckia hirta.

Figure 2-5. Gaillardia pulchella pollen at 400x magnification under a light microscope.

A B

C

41

Figure 2-6. Helianthus angustifolius pollen at 400x magnification under a light microscope.

Figure 2-7. Chamaecrista fasciculata pollen at 400x under a light microscope.

42

Figure 2-8. Monarda punctata pollen at 400x under a light microscope.

Figure 2-9. Example frame locations (in grey) for a vegetation survey. The large square

outlined in black is a single plot. The frames are 1 × ½ m PVC rectangles placed randomly in one of ten areas within the plot.

43

CHAPTER 3 RESULTS

Overall Bee Attraction to Native Florida Wildflowers

In order to determine the native Florida wildflower species most attractive to bees,

I analyzed bee attraction to the six dominant blooming species (those species that had

the longest overlapping bloom throughout the study) as well as bee attraction to groups

of wildflowers blooming in three different time periods. Regarding the latter, the

attraction of bees to seasonally dominant flowers is important to know when attempting

to provide year-round floral resources for bees.

Principle Overlapping Flowers

Six of the wildflower species planted attracted large numbers of bees and bloomed

from the first week of June through mid-October. These six species were Chamaecrista

fasciculata, Coreopsis basalis, Coreopsis lanceolata, Coreopsis leavenworthii,

Gaillardia pulchella and Rudbeckia hirta. These were the only wildflowers to bloom for

an extended period of time as well as consistently attract bees. For this study, I

analyzed the number of bee visits/100 blooms/minute for the time period when all six

species had overlapping bloom periods. Some of the wildflowers were significantly more

attractive to bees than were others (F=8, df=5, 524, P<0.01). Of the six main wildflower

species, bees visited G. pulchella significantly more than all of the other species with

the exception of C. lanceolata (Figure 3-1A). During morning hours, C. lanceolata and

G. pulchella were visited by significantly more bees than were C. fasciculata and C.

leavenworthii (F=3, df=5, 265, P<0.01; Figure 3-1B). In the afternoon, bees visited G.

pulchella significantly more than any other wildflower except C. basalis (F=10, df=5,

251, P<0.01; Figure 3-1C).

44

Spring Time Period

The spring sampling time during which the bloom period for most flowers

overlapped occurred from the second week of May through the first week of June. This

was the only time during which the clovers (Trifolium incarnatum and T. repens)

bloomed. Additional blooming plants included C. basalis, C. lanceolata, C. tinctoria, G.

pulchella and R. hirta. Bees visited G. pulchella significantly more than all other plants

except T. repens (F=4, df=6, 89, P<0.01; Figure 3-2A). During morning hours, G.

pulchella had the highest bee visitation rates, but its rates were not significantly different

from those of C. lanceolata, C. tinctoria or R. hirta (F=3, df=6, 37, P=0.02; Figure 3-2B).

In the afternoon, G. pulchella and T. repens were visited by significantly more bees than

were the other wildflowers (F=2, df=6, 43, P=0.05; Figure 3-2C).

Late Summer/Early Fall Time Period

The late summer/early fall period time period lasted from the end of July through

mid-October and is when the Dotted Horsemint (Monarda punctata) produced its main

bloom. C. fasciculata, C. leavenworthii, G. pulchella and R. hirta also were blooming

during this period. Overall, bees visited G. pulchella significantly more than any flower

except R. hirta (F=16, df=4, 326, P<0.01; Figure 3-3A). During AM hours, the flowers

were visited equally by bees with the exception of M. punctata which was visited

significantly less by bees than were any other wildflower species (F=13, df=4, 167,

P<0.01; Figure 3-3B). During the afternoon, G. pulchella was visited by bees

significantly more than were the other wildflower species (F=8, df=4, 152, P<0.01;

Figure 3-3C).

45

Late Fall Time Period

The late fall time period lasted from early October through early November and

was when the Narrow-leaved Sunflower (Helianthus angustifolius) bloomed. C.

fasciculata, C. leavenworthii, G. pulchella, M. punctata, and R. hirta were in bloom as

well. G. pulchella, H. angustifolius, and R. hirta were visited most by bees, though not

more so statistically than C. fasciculata (F=9, df=5, 142, P<0.01; Figure 3-4A). Bees did

not prefer any wildflower species over another one during the am hours (F=2, df=4, 62,

P=0.18). During the afternoon, bees preferred to visit G. pulchella, H. angustifolius and

R. hirta significantly more than the other test wildflowers (F=8, df=4, 72, P<0.01; Figure

3-4B).

Wildflower Visitation by Bee Tribe

Apini (Apidae)

In Florida, the Apini tribe consists of only one species, Apis mellifera Linnaeus or

the Western honey bee. Honey bees visited some wildflower species more than others

throughout the entire sampling season, though no clear patterns were observed (F=26,

df=6, 643, P<0.01; Figure 3-5A).

Spring time period

Although I occasionally saw honey bees at my sites throughout the year, they only

visited the sites enough to analyze flower visitation rates for the spring sampling period.

Honey bees did not visit the wildflower sites enough in summer/fall to analyze those

time periods. During spring, honey bees visited C. lanceolata significantly more so than

the other flower species (F=533, df=2, 69, P<0.01, Figure 3-5B). This pattern remained

true statistically during the morning sampling period (F=387, df=2, 30, P<0.01, Figure 3-

5C).

46

Augochlorini (Halictidae)

Augochlorini is the tribe that contains the green sweat bees. In Florida, it is

composed of the genera Augochlora, Augochloropsis, and Augochlorella. While these

bees are common, I did not see them in sufficient numbers at any time of the year to run

seasonal analyses, so only an overall test (all wildflowers over all time periods) could be

performed. The overall analysis did indicate bee visitation preference for some of the

flowers though the pattern was hard to interpret due to the amount of absence data

(F=594, df=4, 643, P<0.01; Figure 3-6). That said, Augochlorini bees were recorded

from the following plant species: C. fasciculata, C. lanceolata, C. leavenworthii, and G.

pulchella.

Bombini (Apidae)

In Florida, the Bombini tribe consists of six different bumble bee species. Of these

six species, approximately 99% of all bumble bee sightings at my research sites were

either Bombus impatiens Cresson or B. pensylvanicus (DeGeer). Bombus fraternus

(Smith), B. griseocollis (DeGeer) and B. bimaculatus (Cresson) accounted for the

remainder of the bumble bee sightings. B. variabilis Cresson, the sixth and very

uncommon bumble bee parasite species, was never seen. Bumble bees were rarely

present on my research plots in the spring and the late fall, but they were present in

large numbers during the overlapping bloom period of the principle six wildflowers, and

in the late summer/early fall bloom period.

Principle overlapping flowers

For the principle six flower species, bumble bees exhibited a very clear preference

(F=21, df=3, 423, P<0.01). C. fasciculata was visited by bumble bees more than were

the other flowers overall (Figure 3-7A) and during AM hours (F=9, df=2, 220, P<0.01;

47

Figure 3-7B). In the afternoon, bumble bees visited C. fasciculata and G. pulchella

similarly to one another but significantly more so than the other flowers (F=1494, df=2,

195, P<0.01; Figure 3-7C).

Late summer/early fall time period

During late summer/early fall, C. fasciculata was the wildflower most visited by

bumble bees (F=10072, df=2, 276, P<0.01, Figure 3-7D). During AM hours, bumble

bees visited C. fasciculata significantly more than the other wildflower species (F=1617,

df=2, 145, P<0.01, Figure 3-7E). In the afternoon, C. fasciculata, G. pulchella, and M.

punctata were visited more by bumble bees than were the other flowers (F=8114, df=2,

124, P<0.01, Figure 3-7F).

Eucerini (Apidae)

The Eucerini or long-horned bees are a common group in Florida. The species

caught most regularly on my plots were Melissodes communis Cresson and Svastra

aegis (LaBerge). Infrequently found in the spring on my plots, there was insufficient data

to perform an analysis for the principle six or the late summer/early fall bloom periods.

Late fall time period

The long-horned bees were very common in the late fall during the H. angustifolius

bloom. In the overall test, H. angustifolius was visited most (F=11, df=2, 106, P<0.01;

Figure 3-8A). In the morning the long-horned bees visited H. angustifolius significantly

more as well (F=245, df=1, 50, P<0.01; Figure 3-8B). The long-horned bees did not

demonstrate a flower visitation preference during the afternoon observation period (F=2,

df=2, 50, P=0.12).

48

Halictini (Halictidae)

The Halictini tribe contained the most commonly found bee on my research plots,

the primitively eusocial Halictus poeyi Lepeletier. Agapostemon splendens (Lepeletier),

a solitary green sweat bee, is also a member of this tribe and was seen frequently.

Principle overlapping flowers

In the overall test for the principle six wildflower species, Halictini visited G.

pulchella significantly more than all the other wildflowers except C. basalis and C.

lanceolata (F=15, df=5, 423, P<0.01; Figure 3-9A). In the morning sampling period, only

C. fasciculata was not visited significantly by Halictini (F=8, df=5, 220, P<0.01; Figure 3-

9B). During the afternoon sampling periods, G. pulchella was visited significantly more

than were the other flower species with the exception of C. basalis (F=13, df=5, 195,

P<0.01; Figure 3-9C).

Spring time period

In the overall test in the spring, Halictini visited G. pulchella the most numerically,

though its visitation rate was not significantly different from those of C. basalis, C.

lanceolata or R. hirta (F=4, df=5, 69, P<0.01; Figure 3-9D). Similarly, in the morning, C.

lanceolata and G. pulchella were visited significantly more than all but C. basalis and R.

hirta (F=5, df=5, 30, P<0.01; Figure 3-9E). In the afternoon, Halictini visited C. basalis,

C. lanceolata, G. pulchella and T. repens significantly more than the other wildflower

species (F=4, df=5, 30, P=0.01; Figure 3-9F).

Late summer/early fall time period

In the overall test for the late summer/early fall, Halictini visited G. pulchella the

most, though not significantly more so than R. hirta (F=35, df=4, 276, P<0.01; Figure 3-

9G). In the morning, C. leavenworthii, G. pulchella and R. hirta were significantly more

49

visited than the other wildflowers (F=22, df=4, 145, P<0.01; Figure 3-9H). In the

afternoon, G. pulchella, C. leavenworthii, and R. hirta were visited by Halictini more than

was M. punctata (F=4, df=4, 124, P<0.01; Figure 3-9I).

Late fall time period

In the late fall overall test, G. pulchella, H. angustifolius and R. hirta were visited

significantly more than C. leavenworthii (F=4, df=3, 106, P=0.02; Figure 3-9J). In the

morning and afternoon tests, bee visitation across all wildflower species was similar

(F=2, df=3, 50, P=0.22; F=2, df=3, 50, P=0.17).

Megachilini (Megachilidae)

The Megachilini are a tribe of leafcutter bees. The majority of the leafcutter bees

caught and identified were Megachile albitarsis Cresson and M. mendica Cresson,

although smaller numbers of other native species also were identified. It should be

noted that the leafcutter bees used my sites for not only nectar and pollen, but also

were observed cutting pieces of petals off G. pulchella for their nests. The leafcutter

bees were not common in the spring, but were all other times of the year.

Principle overlapping plants

For the principle six wildflowers, leafcutters visited G. pulchella most (F=5, df=5,

423, P<0.01; Figure 3-10A). In the morning, C. fasciculata was visited significantly less

than were the other flowers (F=3, df=5, 220, P=0.03; Figure 3-10B). The analysis of

afternoon flower visitation by leafcutter bees in the afternoon could not be performed

due to insufficient data.

Late summer/early fall time period

In the late summer/early fall overall test, G. pulchella was most visited, though not

significantly more so than C. leavenworthii (F=6, df=3, 276, P<0.01; Figure 3-10C). Bee

50

visitation of flowers in the morning and afternoon did not vary significantly (morning:

F=2, df=3, 145, P=0.21; afternoon: F=2, df=2, 124, P=0.10).

Late fall time period

The overall and morning tests were not significant (F=1, df=3, 106, P=0.42; F=0,

df=3, 50, P=0.99), but the afternoon test for late fall was. In the late fall afternoons

leafcutter bees visited G. pulchella and H. angustifolius significantly more than they

visited the other wildflower species (F=1555, df=1, 50, P<0.01; Figure 3-10D).

Xylocopini (Apidae)

The Xylocopini tribe in Florida consists of only two species of carpenter bees:

Xylocopa micans Lepeletier and X. virginica (Linnaeus). The majority of the carpenter

bees I saw on my research plots were X. micans. I rarely saw carpenter bees on my

plots in the spring and late fall, which probably was due to when the flowers they

preferred in my sites bloomed.

Principle overlapping flowers

For the principle six wildflower species, carpenter bees visited C. fasciculata

significantly more than all other wildflowers (F=958, df=2, 423, P<0.01; Figure 3-11A), a

trend that held true during morning observations (F=2962, df=1, 220, P<0.01; Figure 3-

11B). Carpenter bee visitation rates of flower did not vary among wildflower species in

the afternoon (F=0, df=1, 195, P=0.98).

Late summer/early fall time period

In the late summer/early fall overall test, C. fasciculata and M. punctata were the

most significantly attractive wildflowers to carpenter bees (F=16466, df=1, 276, P<0.01;

Figure 3-11C). In the morning carpenter bees visited C. fasciculata more than any other

flower (F=∞, df=4, 145, P<0.01; Figure 3-11D). The afternoon analysis could not be

51

performed due to low bee flower visitation rates during the afternoon observations. Bee

tribe attraction by season and time of day (Table 3-1) and bee tribe by plant species

(Table 3-2) are summarized.

Pollen Washes

Pollen Wash Means

Only bees visibly carrying pollen were collected, so the number of pollen grains on

each bee was high. Furthermore, the amount of pollen carried by a bee varied by bee

species and plant species (Table 3-3).

Pollen Wash Percentage Likelihood

The pollen wash percentage likelihood data indicate the likelihood that a bee

collected from a particular wildflower species actually has pollen from that wildflower

species on it. This is probably a better indicator of given bee’s pollen collection habits

because some plants naturally produce less pollen than others. For example, oak (a

wind pollinated plant) produces large amounts of pollen, which bees will collect actively.

Many legumes, such as C. fasciculata, do not produce much pollen as they are

pollinated exclusively by insects. As such, they rely on insects to carry their pollen from

flower to flower. In general, bees captured on a particular wildflower species had a high

likelihood of carrying pollen from that species (Table 3-4).

Pollen on Bumble Bees

Bumble bees carrying pollen were caught only on C. fasciculata. Surprisingly,

most of the pollen they carried was not from Chamaecrista, but was from unknown

sources (Table 3-5). Additionally, the bumble bees captured from Chamaecrista did not

always carry Chamaecrista pollen, and a quarter of the time had aster pollen on them

despite only rare sightings of bumble bees on aster flowers (Table 3-6).

52

Pollen on Halictus poeyi

Halictus poeyi, in comparison to bumble bees, were caught only rarely on C.

fasciculata, and instead usually were caught on Coreopsis spp., R. hirta and G.

pulchella. Most of the pollen carried by H. poeyi was from the Asteraceae flowers, with a

few unknown pollen grains and no Chamaecrista pollen grains (Table 3-7). A third of the

bees caught on non-Gaillardia Asteraceae plants had Gaillardia pollen on them, and

almost three quarters of the bees caught on Gaillardia had other Asteraceae pollen on

them as well (Table 3-8). It should be further noted that in the field, H. poeyi frequently

were observed flying from Gaillardia to Coreopsis and back again.

53

Table 3-1. Bee visitation of the tested wildflower species Time Period

Tribe Main Six Spring Late Summer to Early Fall Late Fall Overall Apini NA C. lanceolata�� NA NA NA

Augochlorini NA NA NA NA C. fasciculata, C. lanceolata, C. leavenworthii, G. pulchella

Bombini C. fasciculata���, G. pulchella�

NA C. fasciculata���, M. punctata�, G. pulchella�

NA NA

Eucerini NA NA NA H. angustifolius�� NA

Halictini C. basalis�, C. lanceolata�, C. leavenworthii�, G. pulchella���, R. hirta�

C. basalis�, C. lanceolata��, G. pulchella���, T. repens�

C. leavenworthii��, G. pulchella���, R. hirta��

G. pulchella�, H. angustifolius�, R. hirta�

NA

Megachilini C. basalis�, C. lanceolata�, C. leavenworthii�, G. pulchella��, R. hirta�

NA G. pulchella� G. pulchella�, H. angustifolius�

NA

Xylocopini C. fasciculata�� NA C. fasciculata��, M. punctata�

NA NA

Flower species listed are those significantly attractive to that tribe of bees. Superscripts next to species names mean the following: � = significance differences were present in the overall test, � = significant differences were present in the morning test, � = significant differences were present in the afternoon test. NA means data were not available.

54

Table 3-2. Bee tribe visitation by plant species Apini Augochlorini Bombini Eucerini Halictini Megachilini Xylocopini

C. fasciculata X X X

C. basalis X X

C. lanceolata X X X X

C. leavenworthii X X X

G. pulchella X X X X

H. angustifolius X X X

M. punctata X X

R. hirta X X

T. repens X

X indicates significant visitation in at least one time period. Table 3-3. Pollen wash data

Plant from which bees were captured Pollen found on the bee Aster Gaillardia Chamaecrista Helianthus

Aster 17575±2381(29) 4024±1164(49) 1864±970(31) 155468±154428(4)

Gaillardia 840±386(29) 8647±2094(49) 100±59(31) 9843±8818(4)

Chamaecrista 0±0(29) 0±0(49) 14798±2744(31) 0±0(4)

Monarda 0±0(29) 0±0(49) 665±665(31) 0±0(4)

Helianthus 0±0(29) 31±26(49) 0±0(31) 60000±49339(4)

Unknown 775±538(29) 459±173(49) 142862±45147(31) 1250±510(4)

Data are the mean ± standard error (n) of the estimated number of pollen grains found on an individual bee captured on a given wildflower species.

Table 3-4. Pollen wash percentage likelihoods Plant from which the bees were captured Pollen found

on the bee Aster Gaillardia Chamaecrista Helianthus Aster 100±9%(29) 73±7%(49) 22±9%(31) 75±25%(4) Gaillardia 34±9%(29) 95±7%(49) 9±9%(31) 75±25%(4) Chamaecrista 0±9%(29) 0±7%(49) 87±9%(31) 0±25%(4) Monarda 0±9%(29) 0±7%(49) 3±9%(31) 0±25%(4) Helianthus 0±9%(29) 4±7%(49) 0±9%(31) 75±25%(4) Unknown 41±9%(29) 32±7%(49) 100±9%(31) 75±25%(4)

Data are mean percent likelihood ± standard error (n).

55

Table 3-5. Bumble bee pollen wash means Plant from which the bees were captured Pollen found on

the bee Chamaecrista Aster 1793±1119(23)

Gaillardia 54±54(23)

Chamaecrista 14538±3193(23)

Unknown 168070±59828(23) Data are the mean ± standard error (n) of the estimated number of pollen grains found on an individual bumble bee (Bombus spp.) captured on Chamaecrista fasciculata.

Table 3-6. Bumble bee pollen wash percentage likelihoods Plant from which the bees were captured Pollen found

on the bee Chamaecrista Aster 26±10%(23)

Gaillardia 4±10%(23)

Chamaecrista 91±10%(23)

Unknown 100±10%(23) Data are mean percent likelihood ± standard error (n). Table 3-7. Halictus poeyi pollen wash means

Plant from which the bees were captured Pollen found on the bee Aster Gaillardia Chamaecrista Aster 19170±2468(26) 3344±1174(37) 8281±8281(2)

Gaillardia 625±317(26) 4797±774(37) 625±625(2)

Chamaecrista 0±0(26) 0±0(37) 0±0(2)

Helianthus 0±0(26) 42±35(37) 0±0(2)

Unknown 168±47(26) 135±46(37) 937±313(2) Data are the mean ± standard error (n) of the estimated number of pollen grains found on an individual Halictus poeyi captured on a given wildflower species.

Table 3-8. Halictus poeyi pollen wash percentage likelihoods

Plant from which the bees were captured Pollen found on the bee Aster Gaillardia ChamaecristaAster 100±9%(26) 73±8%(37) 50±35%(2)Gaillardia 35±9%(26) 95±8%(37) 50±35%(2)Chamaecrista 0±9%(26) 0±8%(37) 0±35%(2)Helianthus 0±9%(26) 5±8%(37) 0±35%(2)Unknown 38±9%(26) 24±8%(37) 100±35%(2)

Data are mean percent likelihood ± standard error (n).

56

Figure 3-1. Bee visitation (LS-mean number of bees/100 blooms/minute) on the

principle six wildflower species, i.e., those with the longest overlapping bloom period. LS-Means with the same letter are not different at P ≤ 0.05. Plus/minus bars are standard errors. The graphs are A) overall bee visitation; B) bee visitation during AM hours; C) and bee visitation during PM hours

c b,c a,b b b a

A

B

a,b a b,c a a,b,c c

Based on 3767 observations of bees

Based on 2554 observations of bees

57

Figure 3-1. Continued

C

b a b b a,b c

Based on 1213 observations of bees

58

Figure 3-2. Bee visitation (LS-mean number of bees/100 blooms/minute) on the spring blooming flowers. LS-Means with the same letter are not different at P ≤ 0.05. Plus/minus bars are standard errors. The graphs are A) overall bee visitation; B) bee visitation during AM hours; C) and bee visitation during PM hours

A

b,c b b,c a c d a,b

B

b a,b a,b a a,b c b

Based on 1319 observations of bees

Based on 861 observations of bees

59

Figure 3-2. Continued

C

b b b,c a c d a

Based on 458 observations of bees

60

Figure 3-3. Bee visitation (LS-mean number of bees/100 blooms/minute) on the late summer/early fall blooming flowers. LS-Means with the same letter are not different at P ≤ 0.05. Plus/minus bars are standard errors. The graphs are A) overall bee visitation; B) bee visitation during AM hours; C) and bee visitation during PM hours

A

a,b d a b,c c

B

a a a b a

Based on 1663 observations of bees

Based on 1093 observations of bees

61

Figure 3-3. Continued

C

c b a c b

Based on 570 observations of bees

62

Figure 3-4. Bee visitation (LS-mean number of bees/100 blooms/minute) on the late fall blooming flowers. LS-Means with the same letter are not different at P ≤ 0.05. Plus/minus bars are standard errors. The graphs are A) overall bee visitation; B) bee visitation during PM hours.

A

a,b c a a b a,b

B

d b a a c a

Based on 284 observations of bees

Based on 157 observations of bees

63

Figure 3-5. Apini visitation (LS-mean number of bees/100 blooms/minute). LS-Means with the same letter are not different at P ≤ 0.05. Plus/minus bars are standard errors. The graphs are A) overall bee visitation; B) overall Spring bee visitation; C) Spring bee visitation during AM hours

A

b b b f d b a e a,b a,b c

B

dcg f e a b

Based on 85 observations of Apini bees

Based on 12 observations of Apini bees

64

Figure 3-5. Continued

d cg f e a b

C

Based on 6 observations of Apini bees

65

Figure 3-6. Augochlorini overall flower visitation (LS-mean number of bees/100 blooms/minute). LS-Means with the same letter are not different at P ≤ 0.05. Plus/minus bars are standard errors.

a c a a e a f g a d b

Based on 14 observations of Augochlorini bees

66

Figure 3-7. Bombini visitation (LS-mean number of bees/100 blooms/minute). LS-Means with the same letter are not different at P ≤ 0.05. Plus/minus bars are standard errors. The graphs are A) Principle six overlapping flowers overall bee visitation; B) Principle six overlapping flowers bee visitation by AM; C) Principle six overlapping flowers bee visitation by PM; D) Late summer/early fall overall bee visitation; E) Late summer/early fall overall bee visitation by AM; F) Late summer/early fall overall bee visitation by PM

A

c b e c d a

B

b b e c d a

Based on 694 observations of Bombini bees

Based on 592 observations of Bombini bees

67

Figure 3-7. Continued

C

c a e b d a

D

d b c e a

Based on 102 observations of Bombini bees

Based on 596 observations of Bombini bees

68

Figure 3-7. Continued

E

d b c e a

F

b a a c a

Based on 93 observations of Bombini bees

Based on 503 observations of Bombini bees

69

Figure 3-8. Eucerini visitation (LS-mean number of bees/100 blooms/minute) on late fall blooms. LS-Means with the same letter are not different at P ≤ 0.05. Plus/minus bars are standard errors. The graphs are A) overall bee visitation; B) bee visitation by AM.

A

c a b d

B

c a b d

Based on 97 observations of Eucerini bees

Based on 41 observations of Eucerini bees

70

Figure 3-9. Halictini visitation (LS-mean number of bees/100 blooms/minute). LS-Means with the same letter are not different at P ≤ 0.05. Plus/minus bars are standard errors. The graphs are A) principle six flowers overall bee visitation; B) principle six flowers bee visitation by AM; C) principle six flowers bee visitation by PM; D) Spring blooming flowers overall bee visitation; E) Spring blooming flowers bee visitation by AM; F) Spring blooming flowers bee visitation by PM; G) Late summer/early fall blooming flowers overall bee visitation; H) Late summer/early fall blooming flowers bee visitation by AM; I) Late summer/early fall blooming flowers bee visitation by PM; J) Late fall blooming flowers overall bee visitation

A

b a b a,b a,b c

B

a a a a a b

Based on 2617 observations of Halictini bees

Based on 1674 observations of Halictini bees

71

Figure 3-9. Continued

C

b a b b a,b c

D

a,b a,b c a a,b,c d b,c

Based on 943 observations of Halictini bees

Based on 1252 observations of Halictini bees

72

Figure 3-9. Continued

E

a,b a b,c a a,b d c

F

a a b a b c a

Based on 824 observations of Halictini bees

Based on 428 observations of Halictini bees

73

Figure 3-9. Continued

G

a,b c a b c

H

a b a a b

Based on 748 observations of Halictini bees

Based on 388 observations of Halictini bees

74

Figure 3-9. Continued

I

a b a a a,b

J

a a a b

Based on 360 observations of Halictini bees

Based on 141 observations of Halictini bees

75

Figure 3-10. Megachilini visitation (LS-mean number of bees/100 blooms/minute). LS-Means with the same letter are not different at P ≤ 0.05. Plus/minus bars are standard errors. The graphs are A) principle six flowers overall bee visitation; B) principle six flowers bee visitation by AM; C) late summer/early fall blooming flowers overall bee visitation; D) late fall blooming flowers bee visitation by PM

A

b a b b a,b c

B

a a a a a b

Based on 149 observations of Megachilini bees

Based on 63 observations of Megachilini bees

76

Figure 3-10. Continued

C

b d a a,b c

D

b a a c

Based on 112 observations of Megachilini bees

Based on 22 observations of Megachilini bees

77

Figure 3-11. Xylocopini visitation (LS-mean number of bees/100 blooms/minute). LS-Means with the same letter are not different at P ≤ 0.05. Plus/minus bars are standard errors. The graphs are A) principle six flowers overall bee visitation; B) principle six flowers bee visitation by AM; C) late summer/early fall blooming flowers overall bee visitation; D) late summer/early fall blooming flowers bee visitation by AM

A

c b e b d a

B

c f e b d a

Based on 121 observations of Xylocopini bees

Based on 110 observations of Xylocopini bees

78

Figure 3-11. Continued

C

b a c c a

D

a e d c b

Based on 112 observations of Xylocopini bees

Based on 104 observations of Xylocopini bees

79

CHAPTER 4 DISCUSSION

Benefits of Wildflower Mixes

Multiple investigators have shown that one of the best methods of attracting and

improving populations of native pollinators on agricultural field margins is with sown

wildflowers and bee forage plants (Bäckman & Tiainen 2002; Meek et al. 2002; Pywell

et al. 2005; Pywell et al. 2006; Carvell et al. 2007; Potts et al. 2009). However, not all

wildflower species likely attract pollinators equally nor can one expect them to work well

in all situations. For example, a wildflower species that attracts pollinators well in parts

of Arizona would not do the same in Florida intuitively. To understand the attraction of

native bee pollinators to Florida wildflowers, I developed a study to test the following two

hypotheses: (1) different wildflower species would be attractive to different bee groups

and (2) bee attraction to Florida wildflower species would vary throughout the year. Both

hypotheses were supported by my research.

The data presented herein support work by other investigators who have shown

outside of Florida that different groups of bees, such as honey bees and bumble bees,

preferentially visit different wildflower species (Patien et al. 1993; Carvell et al. 2006;

Tuell et al. 2008; Frankie et al. 2009). Previous investigators also have shown that time

of year can be a factor in pollinator preference (Bäckman & Tiainen 2002; Carreck &

Williams 2002).

Native Bee Use of Wildflower Species

Data are available on bee communities of Florida (Graenicher 1930; Pascarella et

al. 1999; Deyrup et al. 2002; Hall & Ascher 2010) and bee-plant associations

(Graenicher 1930; Mitchell 1960; Balduf 1962; Mitchell 1962; Hardin et al. 1972;

80

Buchmann & Nabhan 1996; Deyrup et al. 2002; Pascarella 2008). Though the data are

survey, rather than comparative data, they coincide with my results in most cases.

These known associations from the literature are summarized in Table 4-1.

For example Svastra aegis, a long horned bee, is known to be an oligolege on

Asteraceae (a composite family), with a strong preference to Helianthus species (Hurd

et al. 1980). My data suggested that even among Asteraceae members, which Eucerini

were seen visiting in my study, the bees in this tribe preferred to visit H. angustifolius.

Halictus poeyi also is known to frequent Asteraceae (Deyrup et al. 2002;

Pascarella 2008). My data demonstrate that H. poeyi prefers Asteraceae flowers,

especially G. pulchella which they preferred over other Asteraceae species during

multiple time periods.

Similarly, bumble bees are listed as polylectic with strong preferences towards

Lamiaceae (mint family), Fabaceae (legume family) and Asteraceae (Pascarella 2008).

Otherwise, they are known to visit a large variety of plants (Deyrup et al. 2002). In my

results, bumble bees preferred C. fasciculata (Fabaceae) most, followed by G. pulchella

(Asteraceae), then M. punctata (Lamiaceae).

In a few cases, my data were inconsistent with literature reports. Xylocopa micans,

the carpenter bee, is known to be polylectic and visits a large variety of flowers (Balduf

1962; Hardin et al. 1972; Deyrup et al. 2002; Pascarella 2008). My data suggest a

preference for only one or two flowers (C. fasciculata and M. punctata). Asteraceae

flowers were seldom visited by X. micans despite the reported carpenter bee use of

multiple Asteraceae species (Deyrup et al. 2002; Pascarella 2008). However, it should

be noted that only the flower species growing in my plots were compared in their

81

visitation by bees. It is entirely possible, even likely, that flowers outside of my plots

were more attractive than the ones in my plots. This is especially likely in the case of

Apis mellifera, which were notably rarely seen in the plots, despite several apiaries

located within 1000 meters of all of my sites. The notable lack of several bee groups at

specific times of the year (such as bumble bees in the spring) leads me to believe that

either none of the wildflowers in those time periods were attractive to those bee groups

or that there were other, far more attractive, wildflowers blooming somewhere in the

vicinity. This is one of the main reasons why I think any future studies should include a

far larger number of wildflower species.

I believe that surveys of bee communities and their floral hosts are a vital first step

in the conservation of bees and pollination services. Controlled comparison tests of bee

flower species use should follow general surveys. They reveal new levels of interactions

between bees and flowers, and narrow our search for good bee forage plants to plants

that the bees actually prefer to use.

Developing a Florida Wildflower Mix That Is Used By Native Bees

One goal of this research was to recommend wildflower species that can be used

to support native bee populations throughout a complete season. Based on the results,

a seed mixture of Chamaecrista fasciculata, Coreopsis basalis, Coreopsis lanceolata,

Coreopsis leavenworthii, Gaillardia pulchella, Helianthus angustifolius, Monarda

punctata, Rudbeckia hirta, Trifolium incarnatum and Trifolium repens would provide

forage for the greatest number and diversity of bees for the longest period of time.

Of the twenty wildflower species tested in this project, only these ten plus

Coreopsis tinctoria either bloomed in sufficient numbers or attracted enough bees to be

used in the statistical tests. This does not mean that the flowers which failed to bloom

82

are of no use to bee pollinators. Several species did not bloom because they are

perennials that begin to bloom only during the second year. For wildflower plantings

allowed to grow more than one season, these might in fact be ideal flowers to use to

attract bee pollinators. However, I was unable to test this assumption.

Furthermore, some of the wildflower species that did not bloom exhibited lower

germination rates or failed to germinate altogether. In many of these cases, the

germination rate of the seeds was known to be low beforehand; however the cost of the

seeds was high, thus prohibiting my ability to compensate for the lower germination rate

by simply planting more seeds. For example, only two Solidago fistulosa Miller

(Pinebarren Goldenrod) bloomed at all and then for only a few weeks in late fall. Despite

this, one of these plants attracted an eighth tribe of bees that I did not mention in the

results section: Colletini. Three of these bees from the genus Colletes were seen on the

goldenrod. In natural settings, goldenrod species are often an important late fall floral

source. It is also a perennial, and individuals that did not bloom this year may have

been overlooked.

The wildflower species that I list above were visited by significant numbers of bees

during at least one time period, but also bloomed well the first year they were planted.

For these reasons I recommend them not only as good bee forage plants, but also as

plants that are easy to grow, hardy and produce a large number of blooms.

I can also recommend them in places besides Florida. Most of the plants used in

this study are found outside of Florida (with the possible exception of Coreopsis

leavenworthii which was until recently considered entirely endemic to Florida). Asclepias

tuberosa Linnaeus, C. lanceolata, C. tinctoria, G. pulchella, M. punctata, R. hirta, T.

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repens and T. incarnatum are all found from Florida to Canada to California. Most of the

rest of the plants are common throughout the eastern United States (USDA, NRCS

2011). Similarly, all of the bee tribes, and even individual bee species are widespread

throughout the United States. For these reasons my study may have applicability

beyond Florida.

Study Limitations

Along with low seed germination rates for some tested wildflower species, there

were several other limitations to this project. First, the study lasted only one field

season. Bee communities have been shown to change drastically from year to year

(Kremen et al. 2004). As such, a number of new species may have been found in the

wildflower plots had it run a second season. However, a bloom period of one year is

indicative of what might occur if these wildflowers are sown on an agricultural field

margin. In this case, only annual wildflowers could be planted beside a field that will be

used only for one season or planted in its place during the fallow year.

Another limitation of the study is that most bee identification occurred in the field

and was accomplished by the sight identification of bees. Some bees such as the

bumble bees, carpenter bees and honey bees are large, common and easily sight

identified. With minor training, a field technician could sight identify these three species.

Other groups of bees, notably many Eucerini and Augochlorini, require a microscope

and dichotomous key to identify to genus or a taxonomic level of greater resolution. To

account for variability between field technicians, I recognized bee tribe as the best level

of resolution I could use in my study. Reference specimens were captured and

identified, thus allowing me to corroborate the sight identifications.

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Further Investigations

While conducting my experiments, I recognized a number of additional studies that

could be conducted. One would be a comparison between two of the main methods

used to compare bee visitation rates: the vegetation survey method and the standard

area method. Both the vegetation survey method and standard area method provide

valuable information. Both provide a measure of bloom density. The vegetation survey

method provides a bloom density based on bloom availability in a mixed wildflower

planting while in the standard area method, wildflower species are planted in uniform

areas, individually by species with a goal of standardizing the number of blooms

available per unit area. Determining bloom density is important for estimating bee use of

flowers. For example, if flower A is very abundant and frequently visited by bees, and

flower B is equally abundant but not visited by bees, flower A can be assumed to be

more attractive to bees. If flower A is very abundant and frequently visited by bees but

flower B is not abundant, then flower B’s apparent unattractiveness to bees could be

due to its rarity or a true lack of preference by the bees for it. Bloom density estimates

allow for standardization of the average bee use of flowers.

The vegetation survey method is what I used in this study. In this method, bloom

density is estimated from repeated vegetation surveys. The vegetation survey

accurately measures the resulting flower mosaic in a plot regardless of the seed

composition of the original common seed mixture. However, sampling personnel must

be able to identify visiting bees and the target plants for this survey method to be useful.

Furthermore, an observer can overlook plant species that do not germinate in large

numbers or favor larger plants that may out shade smaller ones (C. fasciculata for

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example shaded out many of the other species in the annual mix plots until it was

thinned).

The standard area method, on the other hand, does not mimic agricultural field

margin conditions. In a standard area experiment, plant species are planted separately

in individual, standard sized plots. When each plant is labeled accurately, the observer

does not need to be able to identify each plant since the plant is labeled. Raw data

received from this type of survey do not need to be standardized with vegetation survey

data, but can be used as is. Since the survey typically is conducted using a smaller

numbers of plants, the plants need to be in peak blooming conditions to increase study

accuracy. My attempt to conduct this type of survey, per my original proposal, was

unsuccessful due to the poor performance of the plants at the study sites. Ideally, the

study sites should have been located in well-maintained gardens and established to

mimic ornamental gardens rather than agricultural field margins. This would have made

possible higher plant survival rates, a more standardized number of blooms, and greater

numbers and quality of blooms. Viewed in total, vegetation surveys (like those used in

the current study) are best used for agricultural field margin studies while standard area

surveys are more suited to address garden vegetation plantings. As a future

investigation, a comparison of data on bee flower preference collected using both of

these methods would highlight the pros and cons of both methods and may indicate the

effects of plant density and distribution on bee visitation (Cresswell 1997).

Further questions were raised as a result of the implementation of this study. First,

what is the best way to sample bee preference for flowering plants? Pan traps, which

commonly are used to sample for smaller bee species (Roulston et al. 2007), could not

86

be used in this study as they do not provide flower use information, especially when

flowers occur in mixed plantings. Consequently, I had to use sweep netting and sight

identification techniques to survey bees. While more labor intensive than pan trapping,

netting has been proven to be approximately as effective (Roulston et al. 2007) or more

effective at surveying bee communities than pan trapping (Cane et al. 2000; Wilson et

al. 2008).

Another question resulting from this study dealt with temporal sampling

techniques, i.e. what length of time is sufficient to determine bees’ use of wildflowers,

but short enough to avoid repeat sampling of bees? Coupled with sampling time, one

must consider how many sites/plots/flower species can be surveyed accurately in a day

and what manpower is needed to conduct the survey. The ten minute observation

period used in this survey seemed to work well, but a comparison of different

observation periods should be conducted in the future.

Additional temporal sampling issues arose. I found an interaction between time of

day and bee’s flower visitation. Bee plant use habits changed from morning to afternoon

samplings (Table 3-1). It is well known that some bee begin foraging earlier in the

morning than others (bumble bees, for example, are well known to be one of the first

flower visitors). However, it was a surprise to find that most of the bees were more

active on flowers in the morning than in the afternoon. It would be interesting to see if

this holds true in other studies, especially ones taking place in different climates. In

addition, data collection rarely began before 09:00 and usually ended by 16:30. To that

end, it is possible that bees foraging before 09:00 or after 16:30 were sampled

inadequately. This is true especially in the summer months when sunrise was occurred

87

before 06:00. Future investigators could study bee species richness and diversity

throughout an entire day.

Future investigators also could conduct studies that include more wildflower

species. Only commercially available wildflower species were used in my study. Future

studies could include plant species that are not commercially available. The seeds of

many flowering plants can be hand-picked for an experiment. If such species are shown

to be attractive to bees, then seed companies may begin offering them commercially.

Additionally, crop plants may serve as a good addition to any further comparison

studies. Some wildflowers may compete in their attractiveness to crop plants, which

goes against the purpose of planting wildflowers to increase crop production. This is

one of the reasons why the bloom period of different species is so important. When

choosing wildflower species for pollinators of a specific crop it is important to choose

wildflowers that would bloom before and after, but not during, the crop’s bloom. This is

another type of interaction that has yet to be adequately studied.

Additionally, studies should be conducted in other areas and climates to address

unique bee and wildflower communities. Such studies could include woody plants as

well. Bushes that provide good bee forage would be ideal for hedgerows and home

gardens. Furthermore, trees can provide more permanent bee forage, and often are

responsible for winter and early spring nectar and pollen sources. Perennials often have

energy stores and deep root systems that annuals do not have (Mauseth 2009). This

allows them to bloom during droughts or times of the year that annuals cannot.

These investigations may be used to further the study of pollination ecology. It

would be useful to better standardize methods used in pollination ecology and may lead

88

to streamlined methods that take advantage of bee and plant biology. Knowing the pros

and cons of research methods would allow for incoming researchers to better design

their experiments in this quickly expanding field of study. More streamlined methods

would also help to make studies with greater numbers of species and types of plants

possible, leading to a greater enhancement of our knowledge of bee-plant interaction.

Conclusion

Further research into native bees and bee wildflower use will be useful to the long

term conservation of native bees, native plants and the ecological services they provide.

Understanding the links between bees and plants allows us as scientists to predict and

solve problems with pollination services that will occur as a result of habitat loss and

fragmentation, agricultural intensification and the globalization of bee pests and

diseases (National Research Council of the National Academies 2007). As in any

conservation effort, research alone is not enough. Extension and outreach efforts aimed

at convincing growers and homeowners that there is a problem and that they can help

are key steps in the conservation of native bees and other pollinators.

Ultimately native pollinators like the bees seen in my study help maintain a healthy

ecosystem and ensure food security. Our understanding of native bees and their

importance is causing the fields of pollination ecology and pollinator conservation to

blossom. New publications are beginning to bridge the gap between the science and its

application (Kremen et al. 2007; Byrne & Fitzpatrick 2009; Tallamy 2009; Grissell 2010;

The Xerces Society 2011). It is my hope that the work I and others have done will help

to preserve bees and the flowers that feed them for generations to come.

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Table 4-1. Bee-plant associations from literature Bee Genus Known Floral Associations Augochlorella Asclepias, Coreopsis, Chamaecrista, Eryngium, Helianthus,

Monarda, Rudbeckia, Salvia, Solidago, Trifolium, Vernonia

Augochloropsis Asclepias, Chamaecrista, Coreopsis, Eryngium, Helianthus, Solidago, Trifolium

Bombus Asclepias, Baptisia, Chamaecrista, Coreopsis, Eryngium, Gaillardia, Helianthus, Liatris, Monarda, Phlox, Rudbeckia, Solidago, Trifolium, Vernonia

Melissodes Asclepias, Baptisia, Coreopsis, Helianthus, Monarda, Rudbeckia, Salvia, Solidago, Vernonia

Svastra Gaillardia, Helianthus, Vernonia Agapostemon Chamaecreista, Coreopsis, Gaillardia, Helianthus, Monarda,

Solidago, Vernonia Halictus Asclepias, Coreopsis, Eryngium, Helianthus, Liatris, Monarda,

Rudbeckia, Solidago, Trifolium, Vernonia Lasioglossum Asclepias, Coreopsis, Eryngium, Helianthus, Liatris, Monarda,

Rudbeckia, Salvia, Solidago, Trifolium, Vernonia

Megachile Asclepias, Baptisia, Coreopsis, Eryngium, Gaillardia, Helianthus, Liatris, Monarda, Rudbeckia, Salvia, Solidago, Trifolium, Vernonia

Xylocopa Chamaecrista, Solidago, Vernonia

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BIOGRAPHICAL SKETCH

Katharine Buckley graduated in 2011 with a master’s degree in entomology from

University of Florida. She received her bachelor of science in entomology from Purdue

University in August of 2009. As an undergraduate she did research on Florida

mosquito population dynamics as affected by temperature, precipitation and hurricanes.

She plans on pursuing a PhD in entomology, working on native pollinator conservation

and biological control in grapes at Washington State University where she is currently

enrolled.