A new exposure protocol adapted for wild bees reveals species-specific impacts of the sulfoximine insecticide sulfoxaflor

Wild bees are crucial pollinators of flowering plants and concerns are rising about their decline associated with pesticide use. Interspecific variation in wild bee response to pesticide exposure is expected to be related to variation in their morphology, physiology, and ecology, though there are still important knowledge gaps in its understanding. Pesticide risk assessments have largely focussed on the Western honey bee sensitivity considering it protective enough for wild bees. Recently, guidelines for Bombus terrestris and Osmia bicornis testing have been developed but are not yet implemented at a global scale in pesticide risk assessments. Here, we developed and tested a new simplified method of pesticide exposure on wild bee species collected from the field in Belgium. Enough specimens of nine species survived in a laboratory setting and were exposed to oral and topical acute doses of a sulfoximine insecticide. Our results confirm significant variability among wild bee species. We show that Osmia cornuta is more sensitive to sulfoxaflor than B. terrestris, whereas Bombus hypnorum is less sensitive. We propose hypotheses on the mechanisms explaining interspecific variations in sensitivity to pesticides. Future pesticide risk assessments of wild bees will require further refinement of protocols for their controlled housing and exposure.

Acute oral toxicity and risks of four classes of systemic insecticide to 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 determined the acute oral lethal toxicity (48-h LD50) of: the butenolide, flupyradifurone (>1.7 μg/bee); the diamide, cyantraniliprole (>0.54 μg/bee); the neonicotinoid, thiamethoxam (0.0012 μg/bee); and the sulfoximine, sulfoxaflor (0.0177 μg/bee). Compared with published honey bee (Apis mellifera) LD50 values, the present study shows that sulfoxaflor and thiamethoxam are 8.3× and 3.3× 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 10× safety factor, may be sufficient for bumblebee acute oral toxicity. A comparison of five 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 Exposure Toxicity Ratio (ETR), Hazard Quotient (HQ), and Risk Quotient (RQ), primarily because the SRA and FDRA take into account real world variability in pollen and nectar pesticide residues and the chances that bees may be exposed to them.