The objective of this research was to evaluate and develop stable isotope analysis as a tool for (1) reconstructing terrestrial arthropod community structure, and (2) rapidly assessing the effectiveness of conservation biological control techniques in the field. Two systems were used to accomplish these objectives. A natural system, consisting of coyote bush, a gall midge, and its assoicated parasitoids, was used to examine variation in stable isotope signals. We found that a large proportion of the variance in nitrogen isotopic signals was attributable to trophic level. However, other sources of variation must be considered when reconstructing food web structure using isotopic data. A managed system, consisting of cotton and its assoicated edge habitat, was used to test for linkages among terrestrial habitats. Specifically, we quantified the intensity natural enemy foraging from the edge habitat into the cotton fields. Using a combination of carbon and nitrogen stable isotopes, we found that there is a high degree of natural enemy movement and foraging between the edge habitat and the cotton field. However, the intensity of predation between the two habitat types depends in large part on the natural enemy taxa.
Species 1: Diptera Cecidomyiidae Rhopalomyia californica
Species 2: Hymenoptera Platygastridae Platygaster californica
Keywords: trophic relationships, food web
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