Parasitization of drosophilids in Virginia fruit crop environments

1) Sentinel traps for parasitoids (Hymenoptera) of drosophilids were placed in four different small fruit cropping systems during the 2015 field season: cherry, caneberry, blueberry, and wine grape. Traps were placed on the edge and interior of each growing system, and two bait types were used for each site: banana or seasonal fruit respective to the cropping system. In the laboratory, trap baits were seeded with larvae of Drosophila melanogaster, Drosophila suzukii, or Zaprionus indianus, or left uninfested as a control before being placed in the field. Trap baits were left in the field for 3-4 d before being collected and returned to laboratory, where larvae were allowed to finish development in rearing cups. Rearing cups were checked periodically for parasitoid emergence from fly pupae. Active trapping occurred for a total of 21-24 d at each site. Two species of parasitoid were reared from the sentinel trap baits in significant numbers: Leptopilina spp. (Figitidae), a larval parasitoid, and Pachycrepoideus vindemiae (Pteromalidae), a pupal parasitoid, with Leptopilina the most abundant. Both parasitoid species were reared from the cherry orchard, only Leptopilina was reared from the caneberry site, and no parasitoids were reared from the blueberry and wine grape systems. Both species were reared from D. melanogaster, and one individual P. vindemiae was reared from D. suzukii. No parasitoids were reared from Z. indianus.

2) In the laboratory, preliminary studies on parasitization rates of the Leptopilina spp. were performed on D. melanogaster, D. suzukii, and Z. indianus. Results showed 27% parasitization success on D. melanogaster, with 43% more fly mortality than the control. On D. suzukii, there was 0% parasitization success due to effective immune responses, and there was only 12% more mortality than the control, but 73% of emerged flies showed signs of attempted parasitization. There was no indication the parasitoids even attempted to oviposit in Z. indianus larvae, with minimal difference in mortality from the control. Further replicates need to be performed for proper analysis. Studies on parasitization rates of P. vindemiae are in progress.