Effects of genotype and host environment on the cuticular hydrocarbon profiles of parasitoids and aggression by aphid-tending ants.

Parasitoids in the genus specialize on ant-tended aphids and have previously been reported to mimic the cuticular hydrocarbon (CHC) profiles of their aphid hosts to avoid detection by ants. However, the precise mechanisms that mediate reduced ant aggression toward spp. are not known, nor is it clear whether such mechanisms are broadly effective or specialized on particular aphid hosts. Here we explore the effects of wasp genotype and host environment on CHC profiles and ant aggression. Rearing asexual lines in different host aphid environments revealed effects of both wasp line and aphid host on wasp CHCs. However, variation in genotype and host affected different features of the CHC profile, with wasp genotype explaining most variation in linear and long-chain methyl alkanes, while aphid host environment primarily influenced short-chain methyl alkanes Subsequent behavioural experiments revealed no effects of host environment on ant aggression, but strong evidence for genotypic effects. The influence of genotypic variation on experienced ant aggression and relevant chemical traits is particularly relevant in light of recent evidence for genetic divergence among parasitoids collected from different aphid hosts.