Study Confirms Link Between Neonicotinoids and Collapse of Honey Bee Colonies

A new finding provides further evidence that insecticides cause significant harm to honey bee colonies during winters.

Researchers at the Harvard School of Public Health found that the wide use of a class of insecticides called neonicotinoids, causes major harm to honey bee colonies during the colder winters.  

The team in an earlier finding had revealed a strong association between low dose of imidacloprid and Colony Collapse Disorder (CCD), a disorder where the bees were seen leaving the hives over the winter and eventually dying.

Studies done earlier claimed that it was the reduced resistance in the bees to mites or parasites that led to the CCD-related mortality.  The current study led by Chensbeng Lu at HSPH showed that bees in the hives that display CCD carried similar levels of pathogen infestation compared to a group of control bee hives. Most of the control bee hives survived the colder winters. This confirms that neonicotinoids trigger an unknown biological mechanism in bees that eventually lead to CCD.

"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 (Alex) Lu, associate professor of environmental exposure biology at HSPH, said in a statement.

Colony Collapse disorder has been causing a huge threat to the health of the honey bees since 2006. As bees are prime pollinators it is crucial to mitigate the problem.  Environmentalists have zeroed in on several causes that include pathogen infestation, beekeeping practices and pesticide exposure. 

In a study conducted in 2012, Lu found that CCD occurs mainly due to neonicotinoids as they impair the neurological functions of the bees. 

In this study, the researchers examined the health of 18 bee colonies in three different locations in Central Massachusetts from 2012-2013.  In each area, six colonies were separated into three groups in which one was treated with imidacloprid, one was treated with clothianidin and one was left untreated.

The researchers noticed a steady decline in the size of the bee colonies just at the dawn of winters. Early 2013, the population of bees in the control colonies increased but there was a decline among those treated with neonicotinoid. By April, out of 12 just 6 colonies treated with neonicotinoid vanished, which is typical of CCD.  One of the control hives was found with  thousands dead inside. This was similar to a symptom called Nosema Ceranae.

In this study, 12 hives were treated with pesticides and had 50 percent CCD mortality rate.  In the study conducted in 2012, there was a 94 percent mortality rate in the hives treated with pesticides i.e. much higher.

"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," said Lu. "Hopefully we can reverse the continuing trend of honey bee loss."

The study appears online in the Bulletin of Insectology.