Knowing your habitat: linking patch-encounter rate and patch exploitation in parasitoids

According to optimal foraging theory, animals should decide whether or not to leave a resource patch by comparing the current profitability of the patch with the expected profitability of searching elsewhere in the habitat. Although there is abundant evidence in the literature that foragers in general are well able to estimate the value of a single resource patch, their decision making has rarely been investigated with respect to habitat quality. This is especially true for invertebrates. We have conducted experiments to test whether parasitic wasps adjust patch residence time and exploitation in relation to the abundance of patches within the environment. We used the braconid Asobara tabida, a parasitoid of Drosophila larvae, as our model species. Our experiments show that these wasps reduce both the residence time and the degree of patch exploitation when patches become abundant in their environment, as predicted by optimal foraging models. Based upon a detailed analysis of wasp foraging behavior, we discuss proximate mechanisms that might lead to the observed response. We suggest that parasitoids use a mechanism of sensitization and desensitization to chemicals associated with hosts and patches, in order to respond adaptively to the abundance of patches within their environment. Copyright 2004.Asobara tabida; behavioral plasticity; habitat quality; marginal value theorem; optimal foraging; patch-time allocation; travel time