Bees leave their hives and die after exposure to neonicotinoids
By Summit Voice
FRISCO — The closest thing yet to a smoking gun in the ongoing decline of honeybees has emerged. Scientists with the Harvard School of Public Health say their research links systemic neonicotinoid insecticides with colony collapse disorder. The findings contradict suggestions that a parasitic mite is the main cause of the honeybee decline.
After closely tracking the fate of several bee colonies in New England, the researchers said they found that, when bees were exposed to low doses of imidacloprid or clothianidin, they abandoned their hives over the winter and eventually died.
“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.
By carefully monitoring the hives, the scientists were also able to determine that bees in the hives exhibiting CCD had almost identical levels of pathogen infestation as a group of control hives, most of which survived the winter. This finding suggests that the neonicotinoids are causing some other kind of biological mechanism in bees that in turn leads to CCD. The study appeared online May 9, 2014 in the Bulletin of Insectology.
At least one study has documented the linkage between neonicotinoids and bee woes by tracking the use of the systemic insecticide over time and showing how bee die-offs closely follow the initial use of the systemic insecticides. And European food safety experts are also looking at potential human health risks associated with neonicotinoids.
Bee colonies have been collapsing at an unsustainable rate since 2006, creating problems for agriculture — bees pollinate about one-third of all crops globally. Pathogen infestation, beekeeping practices, and pesticide exposure are all suspected as factors, with more and more signs point toward the use of neonicotinoids, which may impair bees’ neurological functions. Imidacloprid and clothianidin both belong to this group.
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—one treated with imidacloprid, one with clothianidin, and one untreated.
There was a steady decline in the size of all the bee colonies through the beginning of winter—typical among hives during the colder months in New England. Beginning in January 2013, bee populations in the control colonies began to increase as expected, but populations in the neonicotinoid-treated hives continued to decline. By April 2013, 6 out of 12 of the neonicotinoid-treated colonies were lost, with abandoned hives that are typical of CCD. Only one of the control colonies was lost—thousands of dead bees were found inside the hive—with what appeared to be symptoms of a common intestinal parasite called Nosema ceranae.
While the 12 pesticide-treated hives in the current study experienced a 50 percent CCD mortality rate, the authors noted that, in their 2012 study, bees in pesticide-treated hives had a much higher CCD mortality rate—94 percent. That earlier bee die-off occurred during the particularly cold and prolonged winter of 2010-2011 in central Massachusetts, leading the authors to speculate that colder temperatures, in combination with neonicotinoids, may play a role in the severity of CCD.
“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.”