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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