Do facultative symbionts influence the outcome of superparasitism in a solitary endoparasitoid?

Facultative endosymbionts can induce a range of costs and benefits within their arthropod hosts. In an infected parasitoid, we hypothesized that such fitness effects may influence larval competitive ability within a superparasitized host. We investigated superparasitism outcomes of a solitary endoparasitoid, Encarsia inaron, to determine if symbionts influence within-host competition. E. inaron is naturally doubly-infected with two facultative endosymbionts, Wolbachia and Cardinium, which have been differentially cured into singly-infected laboratory colonies. Each symbiont is stably transmitted from mother to offspring without horizontal transmission among unrelated individuals. We placed singly-infected wasps onto leaf disks bearing Bemisia tabaci nymphs, observed parasitism events, removed unparasitized hosts, and then observed superparasitism by wasps with the alternate infection status. Superparasitized hosts were reared until wasp emergence and diagnostic PCR was performed to determine symbiont status of the victorious wasp. We found that the population of emerged wasps was evenly split between those bearing Wolbachia and those bearing Cardinium, indicating neither symbiont infection nor order of oviposition significantly influenced the outcome of competition under our experimental conditions (1-3hrs between first and second oviposition). However, we did find a significant male bias in emerged progeny of the superparasitizing wasp, suggesting that wasps are more likely to allocate male offspring to low quality, previously parasitized hosts, and/or that sex of the competitors may influence the outcome of larval competition. Future superparasitism studies will involve virgin females, constrained to lay only male offspring, to determine if sex allocation has masked symbiont effects on competition.