Sulfoxaflor exposure reduces bumblebee reproductive success

Intensive agriculture currently relies on pesticides to maximize crop yield^1,2. Neonicotinoids are the most widely used insecticides globally³, but increasing evidence of negative impacts on important pollinators^4-9 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 scales^13-15. 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.