No. 1 Pesticide Killing Honeybees Harvard study finds more evidence that chemicals are behind colony collapse disorder By John Johnson, Newser Staff Posted May 10, 2014 9:40 AM CDT 33 comments Comments A colony of honeybees. (AP Photo/Haraz N. Ghanbari, File) (Newser) – A new Harvard study adds more evidence to the theory that insecticides are the main culprit in the disappearance of honeybees, reports the Christian Science Monitor. Researchers found that bees in Massachusetts exposed to a common class of insecticides known as neonicotinoids suffered significant drops in numbers over the winter compared with bees who had no such exposure. In the study, only six of 12 colonies exposed to the chemicals imidacloprid and clothianidin survived the winter. Of six non-exposed colonies, all but one made it. Imidacloprid is the world's No. 1 pesticide and has been registered in the US since 1994, says the Monitor. "We demonstrated that neonicotinoids are highly likely to be responsible for triggering 'colony collapse disorder' in honeybee hives that were healthy prior to the arrival of winter," says one of the Harvard researchers, as quoted in the Guardian. The scientists speculate that the chemicals impair the bees' neurological functions, causing them to first abandon their colonies and then die. Based on comparisons with a previous study, the researchers also think that particularly harsh winters can worsen the effects of CCD, reports the Harvard Gazette.