Sulfoxaflor exposure reduces bumblebee reproductive success.

Intensive agriculture currently relies on pesticides to maximize crop yield1,2 . Neonicotinoids are the most widely used insecticides globally3 , but increasing evidence of negative impacts on important pollinators4-9 and other non-target organisms10 has led to legislative reassessment and created demand for the development of alternative products. Sulfoximine-based insecticides are the most likely successor11 , and are either licensed for use or under consideration for licensing in several worldwide markets3 , including within the European Union12 , where certain neonicotinoids (imidacloprid, clothianidin and thiamethoxam) are now banned from agricultural use outside of permanent greenhouse structures. There is an urgent need to pre-emptively evaluate the potential sub-lethal effects of sulfoximine-based pesticides on pollinators11 , because such effects are rarely detected by standard ecotoxicological assessments, but can have major impacts at larger ecological scales13-15 . Here we show that chronic exposure to the sulfoximine-based insecticide sulfoxaflor, at dosages consistent with potential post-spray field exposure, has severe sub-lethal effects on bumblebee (Bombus terrestris) colonies. Field-based colonies that were exposed to sulfoxaflor during the early growth phase produced significantly fewer workers than unexposed controls, and ultimately produced fewer reproductive offspring. Differences between the life-history trajectories of treated and control colonies first became apparent when individuals exposed as larvae began to emerge, suggesting that direct or indirect effects on a small cohort may have cumulative long-term consequences for colony fitness. Our results caution against the use of sulfoximines as a direct replacement for neonicotinoids. To avoid continuing cycles of novel pesticide release and removal, with concomitant impacts on the environment, a broad evidence base needs to be assessed prior to the development of policy and regulation.