Pasquier, L.; Tomas, D.; Labas, V.; Teixeira-Gomez, A. P.; Meunier, J.; Lecureuil, C.

Pesticides are ubiquitous in agroecosystems and pose substantial risks to non-target organisms. Traditional ecotoxicological assessments focus on survival, reproduction, or overt behavior, yet these endpoints may fail to detect subtle, molecular-level stress. Here, we investigated the effects of sublethal deltamethrin exposure on the head proteome of field-collected European earwig (Forficula auricularia) females, sampled at two life stages (pre-oviposition and post-family life) to account for physiological context. Our results reveal that deltamethrin induces a robust proteomic response shared across developmental stages, including the regulation of key detoxification enzymes (NADPH-cytochrome P450 reductase, arginine kinase). In parallel, stage-specific responses were observed, involving proteins related to metabolism, stress response, and cellular organization. Strikingly, these molecular perturbations occurred without detectable changes in reproductive traits, highlighting a disconnect between cellular stress and organismal phenotypes. Several uncharacterized proteins were consistently regulated, representing promising targets for future studies on pesticide adaptation and potential detoxification pathways. Overall, these findings suggest that classical phenotypic assays may underestimate sublethal pesticide effects, and that proteomic profiling provides a sensitive framework to uncover underlying molecular responses. By integrating natural variability, realistic exposure, and reproductive physiology, our study emphasizes the need for molecular approaches in environmental risk assessment and offers a new perspective on the subtle, cryptic effects of agrochemicals.