Non-Target Effects of Neurotoxic Insecticides on Ganaspis cf. Brasiliensis, a Classical Biological Control Agent of the Spotted Wing Drosophila

Background The spotted wing drosophila, Drosophila suzukii, is an invasive pest causing signifcant 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 con‑sequences on non-target species when persisting in the environment at low concentrations after feld 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 infesta‑ tions 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 (LC5 and LC30) 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 LC50 of 1.38× 10–3 g active ingredi‑ent (a.i.) /L, while cyazypyr seemed the safer active ingredient with an estimated LC50 of 0.20 g a.i./L without afect‑ing parasitoids at sublethal doses. Spinosad and phosmet signifcantly reduced wasp survival at both LC30 and LC5, while lambda-cyhalothrin and acetamiprid afected parasitoid lifespan only at LC30. Spinosad, lambda-cyhalothrin and phosmet LC30 caused the major survival reductions, followed by acetamiprid LC30. The least signifcant reduction in parasitoid survival was 21.6% by spinosad LC5. Conclusions Overall, this study highlighted the importance of carefully selecting insecticides to minimize adverse efects on non-target organisms. In particular, cyazypyr was the most promising candidate to integrate inocula‑tive biological control with chemical treatments. By contrast, the application of phosmet, spinosad and lambdacyhalothrin should be avoided alongside parasitoid feld releases. Although acetamiprid is less used against D. suzukii in the feld than the other tested molecules, it should be used with caution due to its sublethal toxicity on the para‑ sitoid. These results provide the frst evidence of G. cf. brasiliensis susceptibility to insecticides in order to promote sustainable and efcient pest management strategies.