Selectivity of synthetic and bioinsecticides on adults of the spotted wing Drosophila and its pupal parasitoid.

Insecticides are a mainstay for controlling the invasive pest Drosophila suzukii (Diptera: Drosophilidae), but their use comes with several drawbacks related to the adverse target and non-target impacts at lethal and sublethal concentrations. While pesticide risk assessments generally emphasize the short-term efficacy of chemicals on arthropods pests, the evaluation of long-term effects is generally limited to beneficials. The aim of this study was to (i) assess the baseline toxicity of conventional and organic insecticides on D. suzukii following residual contact exposure, and (ii) evaluate the impact of insecticide field rates (FR) and sublethal (LC10) concentrations on D. suzukii and its pupal parasitoid Trichopria drosophilae (Hymenoptera: Diapriidae). Based on estimated LC50 values, the organophosphates malathion and chlorpyrifos, and the spinosyns spinetoram and spinosad emerged as the most toxic active substances toward D. suzukii, although all tested insecticides did not affect the fertility of treated D. suzukii females when applied at LC10. Cyazypyr, lambda-cyhalothrin and the two aforementioned organophosphates were the most harmful insecticides on T. drosophilae, exhibiting lethal and sublethal effects on wasp survival and fertility. Spinetoram only affected parasitoid survival at FR, while azadirachtin and spinosad reduced the parasitoid’s fertility only at LC10. No insecticides affected parasitoid sex-ratio at either tested concentration. These results suggest that insecticides can disrupt the biocontrol service provided by T. drosophilae, even at extremely low concentrations. Understating both target and non-target impact of insecticides is crucial for developing accurate pesticide risk assessments and promoting sustainable D. suzukii management strategies that integrate chemical and biological control methods.