Many parasitoids are species-specific in their choice of host. The gregarious endoparasitic wasp Trichopria nigra (Hymenoptera: Diapriidae) was collected from stable fly (Stomoxys calcitrans) pupae in Russia and Kazakhstan and brought to the USDA ARS-CMAVE facility. T. nigra has been reared on flesh fly (Sarcophaga bullata) and black garbage fly (Ophyra aenescens) as well as stable fly pupae. Additionally, this species readily attempts to parasitize house fly (Musca domestica) pupae. The successful rearing in multiple host flies known to be medical and veterinary pests has prompted the question of plasticity of parasitoid behavior; specifically, whether certain generalist parasitoids can be conditioned to preferentially parasitize a specific host species. Three experiments were performed: (1) an arena choice test presenting pupae of S. calcitrans, S. bullata, and M. domestica to parasitoids that were previously exposed for ~24 and ~48 h to one of the abovementioned hosts; (2) an arena choice test presenting S. bullata and S. calcitrans pupae to T. nigra adults reared on one of those species; and (3) a Y-tube olfactometer choice test offering two different pupal types to conditioned wasps. Wasps previously exposed to one fly species’ pupae preferentially attempted to parasitize pupae similar to the species initially conditioned to. Furthermore, a majority of conditioned wasps chose the same pupal type as their conditioning pupae when presented multiple host species in an olfactometer. These results indicate a strong potential for rearing generalist biocontrol insects on an as-needed basis to specifically target pest flies around households and agricultural facilities.