D3122: Augmentative releases of pupal parasitoid Pachycrepoideus vindemmiae for management of spotted-wing drosophila in organic raspberries in the Upper Midwest

Spotted-wing drosophila (Drosophila suzukii Matsumura (Diptera: Drosophilidae)) (SWD) is difficult to manage in organic high tunnel production of primocane-bearing raspberries in the upper Midwest. High tunnels structures can be fitted with fine mesh netting for organic SWD prevention, however total exclusion has been difficult to achieve. The objective was to determine if augmentative releases of laboratory-reared Pachycrepoideus vindemmiae Rondani (Hymenoptera: Pteromalidae) could suppress infestation of SWD in primocane-bearing raspberries in high tunnels. This study was performed in Minnesota, in 2019 and 2020. Raspberry tunnels were artificially infested with adult male and female SWD until infestation reached 50%. Releases of 500 P. vindemmiae occurred weekly in both years, with an additional 1000 parasitized pupae treatment in 2020. In 2019, no treatment differences between harvest dates and proportion of berries infested with SWD were observed. Infestation levels post-parasitoid release averaged 8.2% lower with parasitoids. In 2020, weekly SWD infestation levels were similar in the 1000 parasitoid and no parasitoid treatments. Treatment differences and the decline of berry SWD infestation occurred following the second parasitoid release, whereas infestation continued to increase without parasitoids. At the last sample date, berries collected from tunnels with 500 parasitoids achieved a 39% and 17% reduction in SWD infestation compared to the control and higher release treatments. Our data show that augmentative releases of P. vindemmiae may suppress pest populations over time, however, does not adequately protect fruit from infestation when used as the sole biological control method.