Acute oral toxicity and risks of exposure to the neonicotinoid thiamethoxam, and other classes of systemic insecticide, for the Common Eastern Bumblebee (Bombus impatiens)

The Common Eastern Bumblebee (Bombus impatiens) is native to North America with an expanding range across Eastern Canada and the USA. This species is commercially produced primarily for greenhouse crop pollination and is a common and abundant component of the wild bumblebee fauna in agricultural, suburban and urban landscapes. However, there is a dearth of pesticide toxicity information about North American bumblebees. The present study determines the acute oral toxicity (48-hour LD50) of cyantraniliprole (>0.54 g/bee), flupyradifurone (>1.7 g/bee), sulfoxaflor (0.0194 g/bee), and thiamethoxam (0.0012 g/bee). Compared with published honey bee (Apis mellifera) LD50 values, the present study shows that thiamethoxam and sulfoxaflor are 4.2x and 7.5x more acutely toxic to B. impatiens, whereas flupyradifurone is more acutely toxic to A. mellifera. The current rule of thumb for toxicity extrapolation beyond the honey bee as a model species, termed 10x safety factor, may be sufficient for bumblebee acute oral toxicity. A comparison of three risk assessment equations suggested that the Standard Risk Approach (SRA) and Fixed Dose Risk Approach (FDRA) provide more nuanced levels of risk evaluation compared to the European Plant Protection Organization (EPPO) Hazard Quotient (HQ), primarily because SRA and FDRA take into account real world variability in pollen and nectar pesticide residues and the chances that bees are exposed to them.