A bacterial gene acquired by parasitoid wasps contributes to venom secretion against host defence.

Horizontal gene transfer (HGT) is an important source of gene innovation in prokaryotic and eukaryotic organisms. Several genes acquired by hosts of parasitoid wasps via HGT have been reported to protect hosts from parasitoid wasps. In contrast, little is known about whether HGT-acquired genes in parasitoid wasps are involved in attacking their hosts. Here, we report a prokaryote-type CDP-diacylglycerol synthase (PTCDS) gene that was horizontally transferred into the last common ancestor of two parasitoid wasps, Leptopilina heterotoma and L. syphax, from the bacterial family Rickettsiaceae. We experimentally demonstrated that PTCDS is linked to ensure the appropriate storage amount of venom in the venom reservoir of parasitoid wasps. PTCDS knockdown downregulated the expression of certain vesicle-mediated transport genes, thereby reducing the secretion of venom into venom reservoir without altering its composition. This resulted in a significant increase in the proportion of encapsulated wasp eggs in parasitized hosts, ultimately leading to host immune-mediated killing. We conclude that parasitoid wasps use the foreign gene PTCDS to influence venom amounts against host defence, providing new insight into the arms race between parasitoid wasps and hosts.