Geographic variation among cowpea aphid symbiont communities

Aphis craccivora is a widespread adventive aphid thought to be of Eurasian origin. This aphid can be infected with the facultative endosymbiont Hamiltonella defensa, which has been shown to confer parasitoid resistance in the pea aphid Acyrthosiphon pisum. As part of a larger study on the potential defensive characteristics of H.defensa in A. craccivora, we conducted a survey to determine 1) the prevalence of H. defensa and 2) correlation of H. defensa with observed parasitism across a geographic range. We obtained A. craccivora specimens from several US locations, Japan and Israel and conducted diagnostic PCR for the presence of H. defensa and hymenopteran DNA. We found that H. defensa is widespread among US populations, but is rare in the Israeli and Japanese populations. We detected no parasitism in any of our samples. We cannot yet speculate on the function or origin of H. defensa in Aphis craccivora. Should a defensive phenotype for H. defensa in A. craccivora be confirmed, our data suggest that US populations of this species might be less susceptible to parasitism than their Eurasian counterparts. More broadly, geographic mosaics of endosymbiont infection may have important implications for matching invasive pests with potential natural enemies in classical biological control.