7/31/2019 RT Vol. 8, No. 3 Maps
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34 Rice Today July-September 2009 Rice Today July-September 2009
34 Rice Today July-September 2009 Rice Today July-September 2009
MapS
Rice is produced in landscapes
that range from extrememonocultures to highly diverseareas. Tropical rice elds often
have a great diversity of naturally occurring arthropod groups that
function as predators and parasitoids(see photos above). At least 200species of parasitoids and 150 speciesof predators live in this environment.
Their diversity and abundance arethe key indicators of the degree of
biological control services presentin an ecosystem, such as resisting
pest invasion and regulating pests.Since rice is grown in seasons,
and so does not provide a permanenthabitat for pests, most of themcome and infest elds when riceis planted. They multiply their
Ecosystem servicesfor biological control
in tropical ricepopulation rather quickly. Their
natural enemies, however, tend toprevent their exponential growth.
When rice is harvested, thesenatural enemies take refugein other habitats surrounding
the rice elds. But, as soonas a new crop is established,they too swarm the eldsagain. Generalist predators,
however, such as spiders andcrickets, are less mobile.
Based on this, factorssuch as landscape structure,
habitat diversity, croppingpatterns, and farmers’ cropmanagement practices can greatly affect these groups and the servicesthey provide. These relationships areoften scarcely studied and quantied.
by K.L. Heong, R. Hijmans, J. Catindig, and S. Villareal
At least 200 species
o parasitoids and 150
species o predators
live in tropical rice
felds. Their diversity
and abundance are the
key indicators o the
degree o biologicalcontrol services present
in an ecosystem, such as
resisting pest invasion
and regulating pests.
Our maps show some of thepreliminary results culled froman assessment of predators andparasitoids in rice elds of Luzon
Island in the Philippines (Fig.1). We obtained 3,050 net sweepsamples from 61 sites. Thesesites were selected using remotesensing–derived land-cover data to
assure that the sampling covered arange of landscapes representativeof the fraction of land used foragriculture (Fig. 2). We caught 11,041
predators that represent 109 species
(81 genera), and 6,682 parasitoidsthat come from 156 species (87genera). Note, however, that wecould not determine the species
level of all the insects found.The number of insects caught
at different sites was from 37 to2,518, with a median of 209. Thenumber of species, on the other
hand, was from 11 to 79, witha median of 36. There was aspatial clustering of abundance(expressed as n), species
richness (expressed as Sobs),and biodiversity (expressed asalpha) in parasitoids (Fig. 3) and
predators (Fig. 4). Associations
between species diversity andhabitat and crop management
were very weak and, in most cases,statistically insignicant. The relativestrength of spatial autocorrelation
between sites and the weakness
of more association with local variables suggeither larger-scale processes shape ecosystefor biological control or that our results are
inuenced by sampling artifacts (sampling tagronomic practices, and regions are confou
Although parasitoid and predator biodivclearly closely related to land-use patterns, ta need to establish direct linkages between dindicators and biological control services. O
interest is the effect opractices such as pest
biological control; theselected vegetation th
food resources to paraas nectar-producing the use of ecological emethods to design mohabitat mixes. Furthe
should answer these q
Fig. 1
Fig. 3. Parasitoids.
Fig. 2
Fig. 4. Predators.
Dr. Heong is a senior
entomology and a spintegrated pest mana
Dr. Hijmans is a GIS IRRI. Ms. Catindig, ascientist, and Ms. Vil
researcher, work in Iand Environmental S
Division.
ichneumonid waspsword-tailed cricket wolf spider
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