Neonicotinoids override a parasite exposure impact on hibernation success of a key bumblebee pollinator

This study assessed whether neonicotinoids and/or parasites influence mortality and weight loss of hibernating queen bumble bees (Bombus terrestris). Researchers exposed queens to field realistic levels of the neonicotinoids thiamethoxam (4 ppb) and its metabolite clothianidin (1.5 ppb) during at least part of their larval development. The researchers found that early lifestage exposure significantly reduced the survival of hibernating queens. Exposure to the parasite Crithiadia bombi also significantly reduced hibernation survival. However, the neonicotinoid exposure caused mortality earlier in hibernation than the parasite exposure. The researchers did not observe any synergistic effects between parasite and neonicotinoid exposures.  The neonicotinoid exposures also increased hibernation weight loss of surviving queens. These effects could have significant impacts on bumble bee populations since individual queens are important to population viability.