HoneybeeWikimedia Commons/ Louise Docker

Scientists have found that the massive deaths of honey bees across the world occuring since a decade or so are due to two types of widely used insecticides. The study was conducted by researchers from Harvard University, who indentified the two classes of insecticides known as neonicotinoids- world's most widely used insecticides.

There has been widespread concern regarding the loss of honeybees in many countries across the world as most of the food crops require pollination.

For the study, researchers have examined 18 bee colonies in areas in Central Massachusetts from October 2012 to April 2013. At each area, two colonies were treated with doses of imidacloprid, two with clothianidin and two control hives were untreated.

"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," Guardian quoted Chensheng Lu, an expert on environmental exposure biology at Harvard School of Public Health and who led the work.

"Bees from six of the 12 neonicotinoid-treated colonies had abandoned their hives and were eventually dead with symptoms resembling Colony Collapse Disorder (CCD). However, we observed a complete opposite phenomenon in the control colonies." said the scientists.

Researchers found in the study that while the untreated colonies started to increase, the pesticide-treated colonies declined.

"Although we have demonstrated the validity of the association between neonicotinoids and CCD in this study, future research could help elucidate the biological mechanism that is responsible for linking sub-lethal neonicotinoid exposures to CCD. Hopefully we can reverse the continuing trend of honey bee loss." Lu said in a press release.

Earlier, scientists had suggested that the insecticide, neonicotinoids can lead to CCD by harming the immune systems of bees, thus making them more vulnerable to parasites and disease. However, the new research challenges this theory by finding that all the colonies had almost identical levels of pathogen infestation.