ABSTRACT

Parasitoid wasps are a large group of hymenopteran insects whose larvae develop by feeding on the bodies of other insects. The spatial distributions of both the hosts and the parasitoid larvae influence the mating systems found in these wasps. Specifically, there is a strong tendency towards mating at the emergence site in species whose offspring develop in gregarious clutches and in species that attack clumped hosts. The genetic and sex–determination systems of parasitoids also influence their mating systems. All sexual parasitic wasps are haplodiploid, with unfertilized eggs becoming males. Thus females can produce male offspring without mating. Some species also show complementary sex determination (CSD) with sex determined by the segregation of alleles at a highly polymorphic sex determination locus. A consequence of this is that inbreeding leads to the production of sterile diploid males. There is therefore selection for females to avoid inbreeding in species with CSD and this is achieved via a premating refractory period in Bracon hebetor. However, we also expect sexual conflict with respect to inbreeding as males are probably selected to take all available mating opportunities.

While laboratory studies of parasitoids have yielded considerable insights, there is a need for more field data on mating systems. Laboratory studies are also needed to help delimit the distribution of CSD, and to investigate patterns of sperm use and mate choice.