Non-target effects of neurotoxic insecticides on Ganaspis cf. brasiliensis, a classical biological control agent of the spotted wing Drosophila

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Background The spotted wing drosophila, Drosophila suzukii , is an invasive pest causing significant economic losses worldwide. Current pest control strategies mainly rely on insecticides, which negatively impact fruit marketability and the sustainability of integrated pest management (IPM) programs. In addition, pesticides can have dramatic consequences on non-target species when persisting in the environment at low concentrations after field applications. In this context, chemical control can strongly interfere with the releases of the G1 strain of the Asian larval parasitoid Ganaspis cf . brasiliensis , which is currently the adopted classical biological control agent to manage D. suzukii infestations worldwide. Methods Probit analysis was used to assess the baseline toxicity of acetamiprid, cyazypyr, lambda-cyhalothrin, phosmet, and spinosad on G1 G. cf . brasiliensis adults through residual contact exposure in the laboratory. Then, adult parasitoids were exposed to insecticide low Lethal Concentrations (LC 5 and LC 30 ) and their mortality was checked daily to assess the survival of treated wasps. Results Lambda-cyhalothrin showed the highest toxicity on the parasitoid with a LC 50 of 1.38 × 10 –3 g active ingredient (a.i.) /L, while cyazypyr seemed the safer active ingredient with an estimated LC 50 of 0.20 g a.i./L without affecting parasitoids at sublethal doses. Spinosad and phosmet significantly reduced wasp survival at both LC 30 and LC 5 , while lambda-cyhalothrin and acetamiprid affected parasitoid lifespan only at LC 30 . Spinosad, lambda-cyhalothrin and phosmet LC 30 caused the major survival reductions, followed by acetamiprid LC 30 . The least significant reduction in parasitoid survival was 21.6% by spinosad LC 5 . Conclusions Overall, this study highlighted the importance of carefully selecting insecticides to minimize adverse effects on non-target organisms. In particular, cyazypyr was the most promising candidate to integrate inoculative biological control with chemical treatments. By contrast, the application of phosmet, spinosad and lambda-cyhalothrin should be avoided alongside parasitoid field releases. Although acetamiprid is less used against D. suzukii in the field than the other tested molecules, it should be used with caution due to its sublethal toxicity on the parasitoid. These results provide the first evidence of G . cf. brasiliensis susceptibility to insecticides in order to promote sustainable and efficient pest management strategies.

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