Sulfoxaflor modulates diet-dependent effects on bumble bee development but shows no detectable effects on adult...

Pollinators face stressors, including pesticide exposure and poor nutrition, yet their combined effects on developing brood remain poorly understood. In this study, we experimentally reared bumble bee (Bombus terrestris) larvae on pollen diets differing in protein-to-lipid ratios and exposed them to the insecticide sulfoxaflor via their food to test how these factors jointly affect survival, development, and adult traits. Larvae fed multifloral pollen exhibited higher survival and more consistent growth than monofloral (oilseed rape, faba bean) diets. Under the oilseed rape, sulfoxaflor reduced mortality and increased adult emergence despite poorer baseline performance in controls. In contrast, under the multifloral diet, sulfoxaflor prolonged development, reduced larval growth, and lowered adult body mass. Responses under faba bean varied among traits, with prolonged development at lower exposure and reduced growth at higher exposure. Despite these developmental effects, larval exposure to sulfoxaflor did not significantly affect adult respiration rate, and respiration patterns showed no significant treatment effects, although diet-dependent trends were observed. These findings demonstrate that sulfoxaflor effects are strongly context-dependent and mediated by nutritional conditions. They indicate that sulfoxaflor shifted diet-dependent trade-offs between survival and development, improving survival under nutritionally limiting diets while imposing developmental delays and growth costs when nutrition was favourable.