Scientists in France have discovered that honey bees are at a higher risk of dying from infection by Nosema ceranae (N. ceranae) when they are exposed to low doses of insecticides. The results, presented in the journal PLoS ONE, support the theory that combining more N. ceranae with high pesticide content in beehives could contribute to colony depopulation.
The French study, “Exposure to Sublethal Doses of Fipronil and Thiacloprid Highly Increases Mortality of Honeybees Previously Infected by Nosema ceranae,” brought together researchers from the Laboratoire Microorganismes: Génome et Environnment and the Laboratoire de Toxicologie Environnment who utilized their respective skills in parasitology and toxicology to assess the effect of pathogen/toxin interactions on bee health. In the laboratory, the researchers chronically exposed newly emerged honey bees, some healthy and others infected with Nosema ceranae, to low doses of insecticides: fipronil and thiacloprid. They found that the infected bees died when they were chronically exposed to insecticides, even at sublethal doses, unlike the healthy bees. This combined effect on honeybee mortality was observed with daily exposure to extremely low doses (over 100 times less than the LD50 or dose needed to kill 50% of the sample population, for each insecticide).