Two Studies Link Insecticides to Colony Collapse Disorder

Monday Jul 7 | BY |
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Two recent studies add evidence to the idea that insecticides are killing off honeybees.

A couple years ago, we did a post on the four reasons why our honeybees are disappearing. Starting in about 2006, beekeepers noticed that their honeybees were vanishing, with no evidence of disease or predators. The USDA states the total number of managed honeybee colonies had decreased from 5 million in the 1940s to only 2.5 million today. Annual losses between 2006-2011 averaged about 33 percent each year.

Scientists called it Colony Collapse Disorder (CCD). Considering about 130 crops in California alone require honeybees to thrive, the situation is serious, and researchers have been struggling every since to figure out what is causing the bees to disappear.

Disease, radiation, environmental stressors (such as limited access to clean water) and pesticides have all been named as potential culprits in CCD, with some believing the real cause may be a combination of all factors. Any definitive answer has remained elusive.

Previous research has made the connection between CCD and the insecticides called “neonicotinoids” used to coat corn seeds, canola and sunflower. Though less toxic than most insecticides to mammals, they were also believed to be less toxic to beneficial insects like bees. Recent studies have questioned that.

Beekeepers noticed honeybees dying around the time of corn planting when these seeds were used. In the summer of 2013, over 50,000 honeybees died when a contractor sprayed 55 trees with a potent neonicotinoid called “dinotefuran.”

The problem with these insecticides is that they can be applied to the soil, after which the plant actually absorbs the chemicals and later expresses them through nectar and pollen—on which honeybees feed. Some European countries have already banned some uses of these insecticides for these reasons.

Now, a new study adds evidence to the neonicotinoid connection.

Studies Link Insecticides with CCD

In 2010, researchers from the Harvard School of Public Health conducted a study in Worcester County to see if a neonicotinoid called “imidacloprid” could be responsible for CCD. Over a 23-week period, they monitored bees in four different yards. Each yard had four hives treated with different levels of imidacloprid and one control hive.

After 12 weeks, all the bees were alive, but after 23 weeks, 15 of the 16 imidacloprid-treated hives had died. Those exposed to the highest levels died first, but overall, it took less imidacloprid to cause the hive collapses than what is typically used in crops or in other areas where bees forage. Researchers noted that the characteristics of the deaths were the same as with CCD—hives were empty, with a few dead bees nearby. The results were published in 2012.

The same group of researchers conducted a second study that they just published in May 2014. This time, they studied the health of 18 bee colonies in three locations in central Massachusetts from October 2012 through April 2013. They separated the bees into six colonies, with three groups within each colony. One was treated with imidacloprid, one with another neonicotinoid called “clothianidin,” and one that wasn’t exposed to the insecticide.

By April 2013, six out of the 12 colonies had died, with the same CCD-type abandoned hives. One of the control hives also died, but researchers found thousands of dead bees in the hive with symptoms of a common intestinal parasite.

Europe Bans Neonicotinoids

Though both studies found that the insecticides killed bees, many more were killed in the 2012 study than in the later one. Researchers theorized that the colder temperatures and prolonged winter experienced in the first study may have made it more difficult for the bees to survive the insecticide exposure. More specifically, they suggested the exposure to the pesticides impaired the bee’s ability to winterize, resulting in more deaths when the winter was particularly cold and long.

The U.S. Department of Agriculture, the Bee Informed Partnership, and the Apiary Inspectors of America reported that U.S. beekeepers lost more than one in five honeybee colonies in the winter of 2013-2014. This was fewer than the winter before, but still a substantial loss.

In April 2013, the European Commission voted to ban the use of both imidacloprid and clothianidin, as well as thiamethoxam, a third neonicotinoid, on all flowering crops used by honeybees. They decided to do so based on the number of scientific studies linking the insecticides to CCD, and have set the ban for two years to see how it affects bee populations.

Manufacturers continue to deny the potential harm to bees. So far in the U.S., there has been no ban. Action has been limited to recommendations about “best management practices.”

What do you think about these studies? Do you think the U.S. should ban these insecticides?

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Karen Feldscher, “Pesticide tied to bee colony collapse,” Harvard School of Public Health,

Marge Dwyer, “Study strengthens link between neonicotinoids and collapse of honeybee colonies,” Harvard School of Public Health, May 9, 2014,

“European Union Protects Bees but U.S. Continues to Allow Neonicotinoid Pesticides,” Natural Resources Defense Council, July 16, 2013,

Colleen M. Story

Colleen M. Story

Colleen M. Story, a northwest-based writer, editor, and ghostwriter, has been creating non-fiction materials for individuals, corporations, and commercial magazines for over 17 years. She specializes in the health and wellness field, where she writes and ghostwrites books, e-books, blogs, magazine articles, and more.

Colleen is the founder of Writing and Wellness. Her fantasy novel, “Rise of the Sidenah,” was released with Jupiter Gardens Press in September 2015. Her literary novel, “Loreena’s Gift,” is forthcoming in spring 2016 from Dzanc Books. She lives in Idaho.


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