Multifaceted sublethal effects of neurotoxic insecticides on olfactory-mediated orientation in the spotted wing drosophila

: Neurotoxic insecticides are recognized and classified by their primary mode of action, but they frequently exhibit secondary targets and downstream consequences that are often neglected. Hazards to arthropod physiology and behavior can sublethally occur through environmentally relevant pesticide residues and/or by contact with non-targeted developmental stages. Drosophila suzukii is a key invasive pest of soft-skinned fruits and provides a suitable model to study how neurotoxicants interfere with olfactory-mediated orientation, a key process underlying host detection and oviposition. However, information on how neurotoxic insecticides influence olfactory-driven orientation behavior in this pest remains undocumented. This study investigated the sublethal effects of neurotoxic insecticides (chlorpyrifos, cyazypyr (cyantraniliprole), lambda-cyhalothrin and spinosad) at realistic occurrence ranges (i.e., estimated lethal concentrations 10%, LC10) on adult female orientation. Contamination occurred either by residual contact at the adult stage or ingestion during larval development. Behavioral responses were assessed using a Y-tube olfactometer, while electroantennography (EAG) and quantitative expression of nine olfactory receptor (Or) genes evaluated peripheral sensorial capacity. Under adult residual contact exposure, chlorpyrifos and spinosad disrupted olfactory orientation in adult flies. In addition, these insecticides, together with lambda-cyhalothrin, increased decision-making time. Residual exposure reduced antennal sensitivity and downregulated Or gene expression. In contrast, following larval ingestion, all tested insecticides induced adult behavior disorientation without detectable effects on peripheral olfactory function. Overall, these findings highlight the importance of considering multiple exposure pathways and sublethal neurotoxic effects when evaluating insecticide hazards on targeted insects, with implications for D. suzukii ecology and the efficacy of olfactory-based integrated pest management strategies.