A nearly three-decade-old mystery of mass honeybee mortality appears to have been solved by researchers in the UK. The collapse of bee colonies in France during the mid- to late-1990s was widely blamed on the neonicotinoid insecticide imidacloprid, but new research has revealed the likely culprit to be the much less high-profile fipronil. Imidacloprid hit the market in 1994 and fipronil was released in 1993, with both products being widely used on French sunflower crops.

A team from the University of Exeter quantified the toxicity and likely bioaccumulation of fipronil, imidacloprid, and two other commonly applied pesticides, in honeybees. They used a computer simulation of a honeybee colony to measure the effects of the pesticides, and ultimately found that only fipronil produced mass mortality.

Specifically, the simulations predicted 4000 to 9000 more bee deaths than control conditions during the first week of fipronil exposure, leading to colony collapse in just two or three weeks. Meanwhile, the other three pesticides didn’t generate mortality rates high enough to cause colony collapse.

The researchers also used gas chromatography-mass spectrometry (GC-MS) to test for bioaccumulation of these compounds, and only found signs of toxic bioaccumulation with fipronil. Their assays showed fipronil ingested by a honeybee in a single meal was present six days later, and the compound could therefore be lethal in even trace doses. Imidacloprid on the other hand did not appear to bioaccumulate in individual bees, and rapid post-exposure recovery was observed in honeybees as well as other insects, indicating reversible binding.

Keep reading and find the original article here: https://www.chemistryworld.com/news/fipronil-responsible-for-historic-honeybee-die-off-/3009865.article