Diversity and abundance of natural enemies of Drosophila suzukii in Wisconsin, USA fruit farms

The invasive vinegar fly, Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), is a major economic pest of soft-skinned fruit in the USA. In order to identify suitable biological control agents in Wisconsin, we assessed the presence and impact of potential natural enemies of D. suzukii in tart cherry and raspberry farms with documented D. suzukii populations. Yellow sticky cards and sentinel traps baited with D. suzukii or D. melanogaster larvae and pupae were deployed in these agricultural areas in the foliage and near the soil surface. Four families of parasitoids with known species that successfully parasitize D. suzukii (Pteromalidae, Braconidae, Figitidae, and Diapriidae) were found on sticky traps at all sampling sites. However, no parasitoids emerged from D. suzukii or D. melanogaster sentinel larvae or pupae throughout the duration of the field assessment. Predation was documented on sentinel D. suzukii pupae (1-4%) and sentinel D. melanogaster pupae (5-8%). The majority of sentinel pupae never emerged upon their return from the field and showed no evidence of field predation. Between 70 and 92% of recovered D. suzukii pupae were dead, and 46-72% of D. melanogaster pupae were dead. The absence of parasitoids found emerging from the sentinel drosophilid larvae and pupae and overall low levels of predation suggests that native biological control may provide limited potential as a management option against D. suzukii in Wisconsin at this time.