Neonicotinoids negatively affect life-history traits in widespread dung fly species

Pesticide use is increasing worldwide, negatively affecting ecosystems, including beneficial insects. The widespread use of neonicotinoid insecticides raises concerns due to their unintended effects on non-target beneficial organisms. Even at sublethal levels, these chemicals can impair development, disrupt physiology, and affect reproduction in both sexes. The impact of larval exposure on key decomposers, that are important for sustaining ecological functions in farmland areas, remains poorly understood. Closing this knowledge gap is essential to fully assess the broader ecological consequences of neonicotinoids. Here, we examined the impacts of the neonicotinoid Imidacloprid on four beneficial dung-decomposing black scavenger fly species: Sepsis thoracica, S. punctum, S. fulgens, and S. cynipsea. Larval exposure to Imidacloprid reduced survival rates, delayed development, and decreased sex-specific body size, to varying degrees among species. While adult females exposed to contaminated dung mated and laid eggs, their first-clutch fecundity was lower compared to controls. Egg hatching success was unaffected regardless of the exposed sex, but total offspring numbers were reduced at the highest pesticide concentrations. Our findings demonstrate that Imidacloprid significantly disrupts larval development and adult reproduction in dung-decomposing insects. These results highlight the potential threats that seemingly benign pesticides pose to biodiversity for non-economic insect species. The consistency of effects across species underscores the broader threat of toxic agents to biodiversity and therefore likely to ecosystem stability.