Two widely used neonicotinoids – a class of insecticide – appear to significantly harm honey bee colonies over the winter, particularly during colder winters, according to a new study from the Harvard School of Public Health (HSPH).
The study replicated a 2012 finding from the same research group that found a link between low doses of neonicotinoids and Colony Collapse Disorder (CCD), in which bees abandon their hives over the winter and eventually die.
“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,” said lead author Chensheng (Alex) Lu, associate professor of environmental exposure biology at HSPH. “Hopefully we can reverse the continuing trend of honey bee loss.”
Since 2006, there have been significant losses of honey bees from CCD. Pinpointing the cause is crucial to mitigating this problem since bees are prime pollinators of roughly one-third of all crops worldwide. Experts have considered a number of possible causes, including pathogen infestation, beekeeping practices, and pesticide exposure.
Neonicotinoids were banned last year in the European Union.
Lu and his co-authors from the Worcester County Beekeepers Association studied the health of 18 bee colonies in three locations in central Massachusetts from October 2012 through April 2013. At each location, the researchers separated six colonies into three groups: two groups were treated with two different neonicotionids, while the third was untreated.
The researchers found a steady decline in the size of all the bee colonies through the beginning of winter, which is typical among hives during the colder months in New England. But beginning in January 2013, when bee populations in the untreated control colonies began to increase as expected, the populations in the neonicotinoid-treated hives continued to decline. By the end of the study, the 12 pesticide-treated hives experienced a 50 per cent CCD mortality rate.
Only one of the untreated control colonies was lost with what appeared to be symptoms of a common intestinal parasite called Nosema ceranae.
Photo credit: Treesha Duncan/Creative Commons