Seasonal occurrence of resident parasitoids associated with Drosophila suzukii in two small fruit production regions of Italy and the USA

For the first time we report the results of a survey to determine the presence, seasonal phenology and biological control status of indigenous parasitoid populations utilizing Drosophila suzukii (Matsumura) and Drosophila melanogaster Meigen (Diptera: Drosophilidae) as hosts in Trento Province, Northern Italy, and the Willamette Valley, Oregon, U.S.A. Larval and pupal parasitoids were sampled using sentinel traps baited with larvae of D. suzukii or D. melanogaster, or traps baited with fruit or yeast-based host substrates. Two generalist parasitoids, Pachycrepoideus vindemiae (Rondani) (Hymenoptera: Pteromalidae) and Leptopilina heterotoma (Thomson) (Hymenoptera: Figitidae) emerged from the sentinel traps in both regions, and a third generalist parasitoid, Trichopria drosophilae Perkins (Hymenoptera: Diapriidae), was found in Italy. L. heterotoma was present during the early portion of the season in Italy while P. vindemiae was found throughout the growing season in both production regions. Low numbers of parasitoids relative to initial larval load in baits suggest a limited effect of indigenous parasitoids on D. suzukii in these two important fruit production regions. These findings highlight the need for improved biological control of D. suzukii through introduction or augmentation of specialist parasitoids from D. suzukii’s native range. This report provides baseline data on the current status of biological control of D. suzukii in Italy and Oregon.