Mechanisms and evolution of host specificity in aphelinid parasitoids of aphids

Abstract

The mechanisms and evolution of host specificity have implications for the explosive diversification of parasitic hymenoptera and for the safety biological control introductions.  Using research on the host specificity of Aphelinus species, which are parasitoids of aphids, I discuss four approaches. The first approach is to study the behavioral and ecological basis of host specificity in laboratory experiments.  These experiments revealed a wide variety of mechanisms underlying differences specificity and showed that host specificity does not appear to be behaviorally dynamic. The second approach is to study phylogenetic and phylogeographical patterns. Results showed that host specificity is often not phylogenetically conserved and that variation in parasitism among populations within a species suggests adaptation to locally abundant aphids. The third approach is to determine the response to selection and the genetic architecture of host specificity.  Laboratory selection for parasitizing a rarely used aphid species gave a more rapid shift in host specificity than expected.  Interspecific crosses and backcrosses to map quantitative trait loci affecting parasitism of a novel host species showed that changes in a few loci were involved. Whole genome scans revealed local hot spots of differentiation between species, which may be associated with differences in host specificity.