Global populations of Aphis craccivora show a high diversity of facultative endosymbionts

Facultative bacterial symbionts can perform a variety of functions for their insect hosts, including defense against parasitism and fungal pathogens ,impact tolerance of heat stress, and improved use of host plants.  These functions may have important ecological and evolutionary consequences for the host, but will depend on the distribution of symbionts within and among host populations.  At present, we know very little about such distributions.  Among aphids, symbiont distribution among pea aphid (Acyrthosiphon pisum) populations is the best described, but it remains to be seen whether the pea aphid model is accurate for other aphid species.  My primary objective is to characterize facultative symbiont distribution within and among worldwide populations of the cowpea aphid, Aphis craccivora. To gain insight into symbiont function in A. craccivora, my secondary objective was to determine whether symbiont distribution is correlated with ecological factors such as host plant identity or parasitism pressure across a geographic range.  

Populations of A.craccivora almost always contained one secondary symbiont. The rate of infection at the individual level was low in contrast to the pea aphid, in which almost all individuals test positive. We did not find correlations between symbiont infection and geography; however there was a significant correlation when examining host plant identity.  More broadly, geographic mosaics of endosymbiont infection may have important implications for matching invasive pests with potential natural enemies in classical biological control, be indicative of host association or even global patterns of aphid movement.

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