Tachinid Endoparasitoid Flies do not Rely on Domesticated Viruses, Unlike Multiple Hymenopteran Lineages

Viral domestication, the co-option of integrated viral genes for host functions, has been repeatedly documented in endoparasitoid Hymenoptera. Whether this phenomenon extends to other parasitoid insects remains to be assessed. Here, we tested this hypothesis in tachinid flies, the largest group of non-hymenopteran parasitoids. To this end, we investigated patterns of viral endogenization in 52 genomes, including 37 newly sequenced species. Similarly to hymenopteran endoparasitoids, tachinid genomes were found to display numerous endogenous viral elements (EVEs), primarily derived from insect-infecting viruses with either DNA or RNA genomes. However, the majority of integrated sequences were species-specific, with no evidence of major ancient gene domestication events. In addition, the EVE content did not differ between dipteran parasitoids and their free-living Diptera counterparts. These findings contrast with the recurrent viral domestication observed in endoparasitoid Hymenoptera. This pattern is discussed in light of important attributes of tachinid flies including their lack of venom and perforating ovipositor, and their avoidance of the host immune system.