Effects of starvation and experience on the response of Drosophila to alternative resources.

We examined the effects of starvation and previous diet on the response of Drosophila melanogaster and D. simulans to alternative resources in the field by simultaneously releasing flies from different laboratory treatments then comparing the proportions captured on two different types of bait. Starvation altered response in all field releases. In conjunction with each release of starved and unstarved flies, the quality of the alternative resources as feeding and breeding sites was tested in the laboratory. Different kinds of tests often produced different rankings, making it difficult to rank resource quality unambiguously. Tentative rankings could be assigned when a resource that was slightly inferior by one criterion was greatly superior by another. Based on these rankings, two of three sets of resource comparisons support the hypothesis that unstarved flies are captured relatively more frequently on better resources than are starved flies. We also tested the effect of prior adult exposure to one of two alternative rotted fruits by comparing the proportions captured on each fruit in the field. Unlike previous studies, we found no systematic effects.