Colony Collapse Disorder (CCD), or the widespread population loss of honeybees, may have been caused by the use of neonicotinoids, according to a new study out of Harvard University.

Neonicotinoids are a class of pesticides, chemically similar to nicotine. They were first developed for agricultural use in the 1980's by petroleum giant Shell. The pesticides were refined by Bayer the following decade.

Two of these chemicals are now believed to be the cause of CCD, according to the new study from the School of Public Health at the university. This study replicated their own research performed in 2012.

Researchers studied 18 bee colonies, located in three areas of Massachusetts. One of these colonies was treated with imidacloprid, the second with clothianidin, and the third colony was left untreated, to act as a control.

When the cold New England winter came, populations in all three colonies declined. Starting in January, the number of bees in the control hive increased, while the other colonies continued their decline.

"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," Chensheng Lu, lead author of the article detailing the study, said.

Colony Collapse Disorder causes bees to leave their hives over the course of a winter. Without their shelter and the warmth from other bees, the insects quickly die. This problem has become more common since 2006.

"Colony losses from CCD are a very serious problem for beekeepers. Annual losses from the winter of 2006-2011 averaged about 33 percent each year, with a third of these losses attributed to CCD by beekeepers. The winter of 2011-2012 was an exception, when total losses dropped to 22 percent," The United States Department of Agriculture (USDA) wrote on their Web page about the problem.

This one-year drop is considered to small of a sample to be interpreted as an improvement, according to the agency.

Imidacloprid and clothianidin were both found to cause the population losses.

Researchers, as well as the general public, have been questioning the causes of CCD, since populations began to decline. Many theories were put forward, including insecticides, pathogens, and bee-keeping techniques.

Honeybees are essential to providing food for humans, as well as wild animals. They pollinate around one third of all crops consumed by humans and domestic animals.

Study into CCD was profiled in the Bulletin of Insectology.

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