Host-Parasitoid Interactions of Two Invasive Drosophilids in Virginia Fruit Crops

1.) Sentinel traps were used to survey for parasitoids of frugivorous drosophilids in Virginia fruit cropping systems, and determine if parasitoids were attacking invasive flies Drosophila suzukii (Matsumura) and Zaprionus indianus Gupta (Diptera: Drosophilidae) in the field. Two parasitoids of frugivorous drosophilids, Leptopilina boulardi (Barbotin, Carton, and Kelner-Pillault) (Hymenoptera: Figitidae) and Pachycrepoideus vindemiae (Rondani) (Hymenoptera: Pteromalidae), were reared, but only one P. vindemiae was reared from D. suzukii, and no parasitoids were reared from Z. indianus. Most parasitoids were reared from alternate host Drosophila melanogaster Meigen and other wild drosophilids. 2.) The ability of these parasitoids to attack D. melanogaster, D. suzukii and Z. indianus under controlled conditions was tested. Larval parasitoid L. boulardi did not develop on D. suzukii or Z. indianus, just D. melanogaster. Pupal parasitoid P. vindemiae successfully developed on all three fly species, but also increased pupal fly mortality. 3.) Olfactometry was used to ascertain if L. boulardi and P. vindemiae are selective about the type of fruit their hosts feed in. Results showed that among cherry, raspberry, blueberry, grape, and banana, L. boulardi preferred raspberry and banana to cherry, and preferred grape least, but no fruit was most preferred. Insufficient data were obtained for P. vindemiae.

We conclude that parasitoids of Virginia are unlikely to provide effective biological control for D. suzukii or Z. indianus, and classical biological control should be investigated as a pest management option. Olfactometry results indicate tritrophic selectivity by Drosophila parasitoids, suggesting multiple parasitoids could be required for effective biological control.