Researchers in the UK report new evidence that the pesticide fipronil, not the neonicotinoid imidacloprid, caused a massive die-off of honey bees in France from 1994 to 1998. Both pesticides hit the market in the early 1990s. At the time, beekeepers and environmentalists largely blamed imidacloprid for the bee deaths. Now, Philippa Holder and colleagues at the University of Exeter and Fera Science, a UK public-private venture focused on agricultural science, suggest that fipronil used on sunflowers was more likely the culprit (Proc. Natl. Acad. Sci. U.S.A. 2018, DOI: 10.1073/pnas.1804934115).
The scientists quantified the toxicity of both pesticides to honey bees and used bioassays to determine the likelihood that they would bioaccumulate in bees. They then incorporated the information into a simulation to predict mass mortality in a honey bee population at environmentally relevant concentrations. The researchers determined that bees rapidly eliminate imidacloprid from their bodies, but they bioaccumulate fipronil. So over time, after prolonged exposure, fipronil becomes more lethal to them. Fipronil is associated with kidney, liver, and thyroid problems in humans.
Source: C&EN, December 3, 2018