A new study conducted at the Harvard School of Public Health and published in the Bulletin of Insectology has found that two widely used neonicotinoids (pesticides) appear to “significantly harm honey bee colonies over the winter.” And the colder the winter, the more severe the harm. The study replicated a 2012 finding that found a link between low doses of imidacloprid, a neonicotinoid, and Colony Collapse Disorder (CCD) that makes bees abandon their hives and die. A second pesticide called clothianidin has the same effect.
The study also found that reduced resistance to mites or parasites because of pesticide exposure is not the issue in CCD, as scientists have suspected. Bees in hives with CCD had “almost identical” levels of pathogen infestation as a group of control hives, most of which survived the winter. Another biological mechanism that leads to CCD is being caused by the pesticides.
Lead author Dr. Chensheng (Alex) Lu, associate professor of environmental exposure biology at HSPH said in a statement, “we demonstrated again in this study that neonicotinoids are highly likely to be responsible for triggering CCD in honey bee hives that were healthy prior to the arrival of winter.”
There have been significant honey bee losses from CCD since 2006. Bees are the primary pollinators of about one-third of all crops worldwide. If honeybees disappear, mankind will be in serious jeopardy.
The scientists looked at 18 bee colonies in central Massachusetts from October 2012 through April 2013. Six colonies were separated into three groups – one treated with imidacloprid, one with clothianidin, and one left untreated.
There was a steady decline in the size of all of the colonies over the winter, which is typical in New England. In January 2013, the populations in the control colonies increased, but populations in the hives treated with the pesticides continued to decline. By April 2013, half of the neonicotinoid-treated colonies were lost, with abandoned hives. Only one of the control colonies was lost, because of an intestinal parasite.
The authors conducted a similar study in 2012. In that, bees in pesticide-treated hives had a 94% mortality rate. The weather during that study was much colder and more prolonged. The scientists think that colder temperatures in combination with the pesticides play a role in the severity of CCD.