Mated Individual Female N. vitripennis that emerged from field collected pupae were allowed to oviposit in Sarcophaga pupae. Female N. vitripennis were then categorised as carrying or not carrying Arsenophonus nasoniae by PCR assay. Emerging progeny were scored for sex. In this analysis, individuals producing no female offspring were discounted, as this is commonly the result of failure of the female wasp to mate and fertilize eggs. Column A: Female ID Column B: Source population (UK or Switzerland) Column C: Results of PCR assay for A. nasoniae (+ = present, - = absent). Column D: #Female wasp progeny emerging Column E: #Male wasp progeny emerging Column F: Proportion of progeny that were female (Column D/(Column D + Column E))