Compatibility of entomopathogenic nematodes and parasitoids of <i>Drosophila suzukii</i> Matsumura

Numerous natural enemies have been investigated to suppress spotted-wing drosophila, Drosophila suzukii, a pest of small fruits and cherries. Current efforts include widespread releases of an imported figitid parasitoid, Ganaspis kimorum, conserving resident pupal parasitoids and an adventive figitid, Leptopilina japonica, and the application of entomopathogenic nematodes. However, the combined effectiveness of parasitoids and nematodes is relatively unknown. Five laboratory studies examined the combination of G. kimorum or L. japonica with the nematodes Steinernema carpocapsae or S. feltiae. The nematodes were applied to the substrate when wandering D. suzukii larvae were about to pupate. Results showed that the combination of parasitoids and nematodes led to higher pest suppression than either parasitoid or nematode only treatments, with an overall 56% to 83% reduction in D. suzukii emergence relative to the control. In 2 cases, the combination had similar effectiveness as the parasitoid-only treatment. The exposure of parasitized larvae to nematodes lowered parasitoid emergence by 26% to 68%. Two studies exposed pupae recently parasitized by the pupal parasitoids Pachycrepoideus vindemiae and Trichopria drosophilae to S. carpocapsae, and the exposure to nematodes lowered adult parasitoid emergence by 49% and 71%, respectively. Given the potential increase in overall pest control but negative impact on developing parasitoids, the decision to combine approaches may be based on whether the goal is to maximize biological control or to establish parasitoids.