Toward the quantification of predation with predator gut immunoassays: A new approach integrating functional response behavior

Immunological methods have been widely used to identify key predator specie s and qualitatively evaluate predation of target prey. However, despite the quantitative nature of many immunoassays, the translation to number of pre y attacked has been problematic because of the many factors that confound i nterpretation of the strength of the immunoassay response. We developed a n ew predation model that couples the proportion of predators positive for pr ey remains determined by enzyme-linked immunosorbent assay (ELISA), predato r density, and predator functional response to prey density for estimating total prey attacked. We used single cotton plant arenas in the greenhouse t o develop functional response models for two generalist predators, Geocoris punctipes (Say) and Orius insidiosus (Say), preying on Pectinophora gossyp iella (Saunders) eggs. The model was validated and compared with other immu nologically based predation models in multiple plant/multiple predator aren as. Our predation model was relatively accurate in predicting the total num ber of prey attacked by both predator species and was a significant improve ment over previous models that rely on simple assumptions regarding predato r attack rates. The model also improves the predictive capacity of the func tional response model alone by correcting for the number of predators actua lly consuming prey. Sensitivity analyses indicated that model performance w as most sensitive to accurate measurement of input variables such as temper ature and the proportion of individuals positive for prey antigens by ELISA and less sensitive to changes in estimates of prey density. Accurate estim ation of the functional response parameters is also important, especially f or the behavioral parameter defining the decline in plant leaf area searche d with increases in prey density. Limitations of the model and application to the field are discussed.