Drosophila species are natural hosts of the first parasitoid wasp of adult dipterans (Hymenoptera: Braconidae, Euphorinae)

Parasitoid wasps are among the most diverse and specialized insects on the planet, having adapted to exploit insect hosts across most orders and life stages. Despite this remarkable diversity, parasitoid wasps infecting the adult stage of flies have never been described, although euphorines are known to attack adult stages of many other insect orders. Until now, wasps seemed to be restricted to parasitizing dipteran hosts during more vulnerable stages – as eggs, larvae, or pupae. Here we report and describe the biology of a novel parasitoid in the hymenopteran-parasitizing tribe Syntretini (Braconidae: Euphorinae) that utilizes adult Drosophila flies as its host. We rear adult wasps from parasitized wild flies and document classic euphorine interactions with flies for the first time, including host-searching and evaluation, oviposition, and larval emergence. In the lab, oviposition-to-adult development spans 40 days at 21° C. Hosts remain active throughout the 18-day larval development window, but females are sterilized by the growing wasp. We identify influences of host sex on wasp morphology, including body size and flagellomere count. We also show, through field collections and exploration of global DNA datasets, the species is broadly distributed across the eastern United States and naturally infects multiple Drosophila hosts, including the laboratory model Drosophila melanogaster. Our findings expand the known host range of adult-parasitoids to include the order Diptera, improve accessibility of euphorines for laboratory research, and underscore persisting gaps in understanding of Drosophila natural ecology.