Naturally occurring parasitoids of <i>Drosophila suzukii</i> (Diptera: Drosophilidae) and other drosophilids in California fruit regions

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) has become a damaging economic pest of small fruits in the invaded range in the Americas, Europe, and North Africa. This study surveyed naturally occurring parasitoids of D. suzukii and other frugivorous Drosophilidae in California's coastal and interior fruit production regions. Surveys were conducted from 2012 to 2018 through collections of infested fruits and the use of sentinel fruit or host traps. Two pupal parasitoids, Pachycrepoideus vindemiae (Rondani) (Hymenoptera: Pteromalidae) and Trichopria drosophilae (Perkins) (Hymenoptera: Diapriidae) were collected from D. suzukii and other drosophilids; the former species dominated in the interior while the latter species dominated in the coastal region. Two larval parasitoids, Leptopilina boulardi Barbotin et al. and L. heterotoma (Thomson) (Hymenoptera: Figitidae) were collected from drosophilid species other than D. suzukii, and were the dominant parasitoids in the interior and coastal regions, respectively. These four common parasitoids were most active during the spring and fall. The levels of parasitism on D. suzukii were < 10% from field-collected fruits but were as high as 74% in sentinel traps. Pupal parasitoids attacked D. suzukii at a higher rate than D. melanogaster in sentinel traps baited with both fly species. These results are discussed in conjunction with ongoing efforts to introduce larval parasitoids from the fly's native range.