Fipronil blamed for historical bee deaths

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.

Holder, now at Newcastle University, and colleagues suggest that pesticide regulators around the world could benefit from bioassays that discriminate between bioaccumulative and nonbioaccumulative pesticides.

“The potentially severe impact of dietary fipronil highlights the need to identify agrochemicals that cause” time-reinforced toxicity, meaning they bioaccumulate and increase in the body in over time, Holder and colleagues say in their paper.

Although regulators in the European Union banned fipronil for use on crops in 2017, seeds treated with fipronil can still be used in most EU countries until March 31, 2019. Fipronil is also commonly used around the world to control ants, cockroaches, and termites in structures and flea and ticks on pets.

Fipronil contaminated millions of poultry eggs in the EU, Hong Kong, and South Korea last year when a disinfectant company illegally used it on chicken farms to treat mites. Last month, beekeepers in South Africa blamed fipronil for killing more than one million bees. They suspect that wineries in the region near Cape Town legally sprayed it to control ants.