For over a decade, a disease called colony collapse disorder has been destroying bee populations worldwide. Because bees pollinate many of our staple crops, their deaths threaten our food supplies. Now, new evidence is solidifying a case against the likely culprit in their deaths.

Photo by Alex Wild


Researchers have previously argued that colony collapse is being caused by neonicotinoids, a form of insecticide that works by damaging the insects' brain functions and shutting down their nervous systems. After a period of excitability, insects exposed to neonicotinoids are paralyzed and subsequently die.

Now, in a new paper published by Harvard environmental biologist Chensheng Lu and colleagues in Bulletin of Insectology, we have confirmation that hives exposed to neonicotinoids are far more likely to suffer colony collapse than those that aren't. Symptoms of colony collapse disorder (CCD) include wildly unpredictable bee behavior, with bees fleeing their hives in winter and never returning. This seems to fit with exposure to a pesticide that works by interfering with the activity of neurotransmitters in their brains.

According to a release from Harvard University:

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% CCD mortality rate, the authors noted that, in their 2012 study, bees in pesticide-treated hives had a much higher CCD mortality rate—94%. 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.

Some experts questioned these research methods, mostly because Lu and colleagues only studied bees in a very specific region, New England. There appear to be regional variations in CCD, with European bees affected more in some areas than others — and none affected in Australia. In addition, researchers have studied hives that are prone to CCD and yet are not anywhere near places where neonicotinoids are used.



So while more research needs to be done, it's possible that neonicotinoids may have to be removed from our arsenal of insecticides. Ironically, in an effort to protect our crops, we may have been inadvertently destroying them. Without bees, many plants cannot reproduce.

Read the full scientific article in the Bulletin of Insectology