Establishment and parasitism levels of Ganaspis kimorum on Drosophila suzukii in Northeastern Italy: insights from a 4-yr release program

The management of the invasive fruit fly Drosophila suzukii (Diptera: Drosophilidae) still relies on chemical control, despite concerns about pesticide resistance and environmental impact. Integrated pest management strategies are being explored, but current options remain limited and often insufficient. In invaded regions, local natural enemies are mostly generalist pupal parasitoids, which have proven inadequate for controlling this rapidly spreading pest. Conversely, in its native range, D. suzukii is host to more specialized larval parasitoids that may mitigate its impact on fruit crops. Extensive foreign exploration and risk assessments identified the larval endoparasitoid Ganaspis kimorum (Hymenoptera: Figitidae) as the most suitable candidate for classical biological control. In 2021, Italy launched a propagative biocontrol program utilizing a Japanese population of G. kimorum. Here, we present the results from the first 4 yr of releases conducted in Northeast Italy, where the parasitoid was released at 20 different locations. We provide an overview of the monitoring activities at these sites to determine whether G. kimorum has successfully established and to assess its parasitism levels on both the target pest and nontarget species. Results confirmed that G. kimorum is a specialist on D. suzukii and likely does not compete with local parasitoids for reproductive resources. Collected data also suggest that the parasitoid has become established in several locations, and it is gradually expanding its range from the initial release sites. Four years after the initial release of G. kimorum, the data gathered offers valuable insights into the efficacy and ecological implications of this biocontrol strategy.