A team of researchers from the University of Exeter and Fera Science Ltd, both in the U.K. has found evidence that implicates the insecticide fipronil as the culprit behind a massive die-off of honeybees in France in the 1990s. In their paper published in Proceedings of the National Academy of Sciences, the group describes their study of two insecticides that were thought to be behind the die-offs and what they found.