Response to selection for parasitism of a suboptimal, low-preference host in an aphid parasitoid.

Risks of postintroduction evolution in insects introduced to control invasive pests have been discussed for some time, but little is known about responses to selection or genetic architectures of host adaptation and thus about the likelihood or rapidity of evolutionary shifts. We report here results on the response to selection and genetic architecture of parasitism of a suboptimal, low-preference host species by an aphid parasitoid, , a candidate for introduction against the soy bean aphid, . We selected .  for increased parasitism of by rearing the parasitoid on this aphid for three generations. We measured parasitism of .  at generations 2 and 3, and at generation 3, we crossed and backcrossed parasitoids from the populations reared on .  with those from populations reared on and compared parasitism of both .  and among and backcross females. responded rapidly to selection for parasitism of . . Selection for .  parasitism reduced parasitism of , the original host of . . However, parasitism of .  did not increase from generation 2 to generation 3 of selection, suggesting reduced variance available for selection, which was indeed found. We tested the associations between 184 single nucleotide polymorphisms (SNP) and increased parasitism of .  and found 28 SNP loci, some of which were associated with increased and others with decreased parasitism of . . We assembled and annotated the .  genome, mapped all SNP loci to contigs and tested whether genes on contigs with SNP loci associated with parasitism were enriched for candidate genes or gene functions. We identified 80 genes on these contigs that mapped to 1.2 Mb of the 483 Mb genome of .  but found little enrichment of candidate genes or gene functions.