Researchers suspect that two popular pesticides are causing Colony Collapse Disorder, a disastrous decline among honey bees in the U.S. and Europe.
The culprits are imidacloprid and clothianidin, two pesticides in the neonicotinoid class that are commonly used in agriculture, Discover reported.
Scientists earlier thought that mites were responsible for the honey bee decline, but a new Harvard research study focusing on three locations in Massachusetts during winter 2012 to 2013 indicates a link between the pesticides and CCD among bees.
"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," lead author Chensheng (Alex) Lu, associate professor of environmental exposure biology at the Harvard School of Public Health, said in a press release.
Publishing their research in the Bulletin of Insectology, the researchers tracked 18 bee colonies, which were divided into groups and exposed to varying types and levels of pesticides.
The six bee colonies at each of three locations were discretely divided into three groups, one of which was treated with imidacloprid, one with clothianidin and one left untreated.
While the insects declined as normal during the winter season, the researchers found that the populations of the bees exposed to pesticides continued to fall in January, which is when the number of bees in the untreated control group began to increase. Half of the bees in the colonies exposed to the neonicotinoids had perished by the spring, leaving behind empty hives.
In an earlier study, the decline in the honey bee population was even more severe, with scientists recording a 94 percent mortality rate among the insects exposed to pesticides. Conducted in an especially cold Massachusetts winter from 2010 to 2011, the previous study may indicate that dropping temperatures boost the fatal effects of the pesticides.
Besides making honey, bees are crucial to food sources as the main pollinators of about a third of all crops worldwide.
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