New research from the USDA Bee Research Laboratory and Pennsylvania State University shows that a toxic pesticide, imidacloprid, weakens bees and makes them more susceptible to the parasitic fungus Nosema, even when the pesticide is present at extremely low levels. Imidacloprid is one of a new class of pesticides called neonicotinoids whose use in the United States has grown in the past decade. It is commonly used for insect control on food crops and lawns, for flea control on pets, and indoors to kill household pests. As a systemic insecticide, it is absorbed by plants and makes leaves and other plant parts toxic to feeding insects.
“It is a new threat,” says Jeff Pettis, entomologist at the USDA Bee Research Laboratory. “Ten years ago, almost all pesticides were sprayed or dusted topically. Bees only came in contact with drift when they landed on a plant. This new class of pesticide can be expressed in the nectar and the pollen.” While symptoms of neonicotinoid poisoning in honeybees look strikingly similar to CCD (memory loss, navigation disruption, paralysis, and death), Pettis says it is a mistake to lay blame on a single cause. Researchers continue to study the complex interactions that could be causing the bee die-offs.