The evolutionary ecology of resistance to parasitoids by Drosophila

Parasitoids are the most important natural enemies of many insect species. Larvae of many Drosophila species can defend themselves against attack by p arasitoids through a cellular immune response called encapsulation. The pap er reviews recent studies of the evolutionary biology and ecological geneti cs of resistance in Drosophila, concentrating on D. melanogaster. The physi ological basis of encapsulation, and the genes known to interfere with resi stance are briefly summarized. Evidence for within- and between-population genetic variation in resistance from isofemale line, artificial selection a nd classical genetic studies are reviewed. There is now firm evidence that resistance is costly to Drosophila, and the nature of this cost is discusse d, and the possibility that it may involve a reduction in metabolic rate co nsidered. Comparative data on encapsulation and metabolic rates across seve n Drosophila species provides support for this hypothesis. Finally, the pos sible population and community ecological consequences of evolution in the levels of host resistance are examined.