Water-Deprived Parasitic Wasps (Pachycrepoideus vindemmiae) Kill More Pupae of a Pest (Drosophila suzukii) as a Water-Intake Strategy.

Most organisms must ingest water to compensate for dehydration. In parasitic wasps, the importance of water and the behaviors driving its consumption are poorly understood. Here, we describe a water-intake strategy of Pachycrepoideus vindemmiae, a parasitoid of spotted-wing drosophila (SWD, Drosophila suzukii). Longevity measurements indicated that P. vindemmiae benefits from drinking water and from host-feeding on the water-rich hemolymph of SWD pupae. After exposing wasps to different water regimens, we observed increased host-feeding in water-deprived wasps despite honey availability. This resulted in greater SWD mortality because the host-feeding process killed the pupae, and because wasps that engaged in greater host-feeding parasitized more hosts. Behavioral observations showed that the host-feeding time of water-deprived wasps doubled compared to water-fed individuals. Host-feeding did not affect parasitoid offspring mortality. We conclude that P. vindemmiae benefits from ingesting water and that it host-feeds on SWD pupae as a water-intake strategy. These are interesting findings not only because water has rarely been reported as a critical nutrient for adult parasitoids, but especially because preying for the purpose of hydration is not a common strategy in nature. This strategy enhances parasitoid survival and reproduction, with positive consequences for its host-killing capacity and potential as a biocontrol agent.