Sub-lethal effects of thiamethoxam, a neonicotinoid pesticide, and propiconazole, a DMI fungicide, on colony initiation in bumblebee (Bombus terrestris) micro-colonies

This study investigated whether field-realistic exposure to a neonicotinoid insecticide and a fungicide affected nest building or brood production in queenless Bombus terrestris micro-colonies in the laboratory. Bees were exposed to honey water and pollen paste containing field-realistic mean or field-maximum exposure rates of thiamethoxam (1, 10 mu g/kg) or propiconazole (23, 230 mg/kg) for 28 days. Thiamethoxam: Both doses reduced consumption of honey water solution and resulted in fewer wax cells. At 10 mu g/kg, nest building initiation was delayed, fewer eggs were laid and no larvae produced. Propiconazole: Both doses reduced consumption of honey water solution. At 23 mg/kg, fewer wax cells were produced. Thus, at realistic (mean) exposure rates of these pesticides, no adverse impacts on brood production were found. Pesticide-free alternative forage will reduce field exposure by dilution and thus the impact of maximum rates.