Move over, cellular microbes: Symbiotic viruses as key players in parasitoid wasp success

Mutualistic viruses remain a rarity among known animal-microbe symbioses. Yet, several lineages of parasitoid wasps maintain heritable associations with beneficial viruses. Parasitoid wasps use these viruses as biological weapons that they introduce into host insects to subdue host defenses and alter host physiology, thereby promoting successful parasitism. To gain a more comprehensive understanding of beneficial virus evolution, we aim to characterize the functions, genetics, and ecology of novel viruses, including those inherited by the wasps Fopius arisanus and Diachasmimorpha longicaudata, which are important biological control agents for many tropical fruit fly pests. Study of an endogenous nudivirus produced by F. arisanus and an exogenous poxvirus carried by D. longicaudata offer transformative examples of viral symbiosis that expand upon current notions of microbial symbiont evolution and challenge existing ideas regarding the evolutionary processes that govern mutualistic viruses.