Species-specific physiological and molecular responses of three bee pollinators to field-level atrazine exposure

Atrazine is a widely used herbicide, and its residues are frequently detected in bee food sources. However, the impact of field-level atrazine residues on bees remains poorly understood. This study evaluated the effects of 1.1 mg/kg atrazine on three bee species (Apis mellifera, Bombus terrestris, and Osmia excavata), by assessing changes in survival probability, sugar solution consumption, body weight, and gut function (including integrity, transcriptomic and metabolomic analyses). The results showed that 1.1 mg/kg atrazine did not significantly affect mortality or sugar solution consumption in the three bee species. However, it reduced the body weight of A. mellifera but did not affect the other two species. Atrazine exposure was found to compromise the intestinal integrity of both A. mellifera and B. terrestris, while exerting no significant adverse effect on that of O. excavata. Transcriptomic analysis revealed that atrazine exposure induced distinct gene expression changes in each bee species, primarily affecting detoxification, energy metabolism, and hormone synthesis pathways. Metabolomic analysis further indicated that pyrimidine metabolism, tryptophan metabolism, and the citrate cycle (TCA cycle) were pathways commonly enriched across the three bee species. Overall, these results suggest that field-level atrazine exposure may exert species-specific sublethal effects on bee physiology and gut function, underscoring the need for cross-taxa assessments in herbicide risk evaluation.