Releases of the parasitoid Pachycrepoideus vindemmiae for augmentative biological control of spotted wing drosophila, Drosophila suzukii

Spotted wing drosophila, Drosophila suzukii, is native to East Asia but has become a major pest of soft-skinned fruit crops in its invaded range in the Americas, Europe and North Africa. Control efforts are complicated by the seasonal movement of D. suzukii into crops from non-crop or untreated-crop habitats. Biological control may help to suppress D. suzukii populations. However, surveys have found that few parasitoid species attack D. suzukii in North America and Europe, with low levels of parasitism by the pupal parasitoids Trichopria drosophilae and Pachycrepoideus vindemmiae and little or no parasitism by larval parasitoids. Augmentation of these resident pupal parasitoids may be a sustainable tool for D. suzukii management. Most augmentation efforts to date have focused on T. drosophilae, although P. vindemmiae is the more abundant and widespread species in North America. In this study, we tested whether augmentative releases of P. vindemmiae could help control D. suzukii in caneberry hoop houses in Minnesota, Oregon and California. Results were inconsistent. Most trials showed no detectable post-release effects on parasitism or D. suzukii levels, although one trial in Oregon did show elevated parasitism levels in release plots. Larger releases of P. vindemmiae may be needed when D. suzukii numbers are high, or to overcome the effects of suboptimal conditions and/or dispersal.