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Study finds colony collapse disorder may be due to neonicotinoid pesticide

April 12, 2012 | 0 comments

The mysterious problem called colony collapse disorder (CCD) in which bee hives die off is the subject of several new studies - one of which indicts a class of pesticide as a possible culprit.

That new study, from the Harvard School of Public Health, points to a widely used pesticide called imidacloprid as a possible culprit in the collapse of bee colonies.

Chensheng (Alex) Lu, a professor of environmental exposure biology in Harvard's Department of Environmental Health, led a field study showing what he called a link between the chemical and CCD. That study will appear in the June 2012 "Bulletin of Insectology" and was published online April 5.

Lu said the experiment included bee exposures to the pesticide at levels below what it normally present in the real environment.

Farmers have been critically interested in the disorder of honey bees and other pollinators because about one-third of U.S. crops - fruits, vegetables and nuts - are pollinated by bees.

PESTICIDE CARRIES over into corn syrup

The Harvard study looked at the possibility that the increase in colony collapse disorder came from the presence of the pesticide, called a "neonicotinoid" that was introduced in the 1990s.

They found that bees can be exposed in the normal course of their collecting nectar from plants or from high-fructose corn syrup used by beekeepers to feed their bees. According to the scientists, most of the corn grown in the United States has been treated with imidacloprid, which carries over into the corn syrup.

The research was carried out over 23 weeks in the summer of 2010. The research team set up new bee hives in four locations using purchased bees in Massachusetts. Each yard had four hives treated with different levels of imidacloprid and one control hive which was not treated.

In each case, bees were free to forage in their natural environment but were also offered feeders containing high-fructose corn syrup. Many beekeepers offer their bees corn syrup each spring to make up for the possibility that the hive has used up a lot of its food during the winter.

Those feeders were the method Lu used to get the imidacloprid into the hives, in concentrations varying from 20 to 400 parts per billion - below federal limits for the pesticide in corn.

After 12 weeks of imidacloprid dosing, all the bees were alive. But after 23 weeks, 15 out of 16 of the imidacloprid-treated hives had died out.

Lu's conclusion is that the bees succumb to chronic poisoning from the insecticide. Bees exposed to the highest levels of the pesticide died first.

The characteristics of the dead hives were consistent with CCD, said Lu; the hives were empty except for stored food, some pollen, and young bees, with few dead bees nearby. When other conditions cause hive collapse - such as disease or pests - many dead bees are typically found inside and outside the affected hives.

In CCD it appears that bees leave the hive and fail to return for one reason or another. One theory is that the pesticide messes up their navigation system, their memory or their behavior in some way.

Lu's team found that it took very low levels of imidacloprid to cause hive collapse - less than what is typically used in crops or in areas where bees forage.

The Harvard field study backs up other recent studies that pointed to neonicotinoid insecticides as the culprit in CCD.

Bayer: Study "flawed, factually inaccurate"

Bayer CropScience, maker of imidocloprid, this week disputed the findings of Lu's study calling the report "flawed" and "factually inaccurate."

In a statement, the company said the study claims to have established a link between imidacloprid and bee colony collapse, "but the symptoms observed in the study bees are not consistent with, or even remotely similar to, those of Colony Collapse Disorder (CCD). As such, the authors' claims that their study explains the causes of CCD are spectacularly incorrect."

Bayer's statement also called the assumption erroneous that the majority of corn grown in the United States has been treated with imidacloprid. "In actuality, over the past 8 years, the annual percentage of total corn acres in the U.S. treated with imidacloprid has been less than half a percent.

"Thus, the suggestion that imidacloprid is affecting honey bee health via residue found on corn or through corn products is also grossly inaccurate."

Bayer officials also criticized the research study for "unsubstantiated assumptions" and they said the corn syrup concentrations that were used were "far above real-world exposure levels."

"Imidacloprid and neonicotinoid insecticides generally, remain safe and effective management tools to control a wide range of destructive insect pests. Throughout the many years that imidacloprid has been commercially available and used, there has been no credible scientific evidence demonstrating a link between this active ingredient - or other neonicotinoids - and increases in honey bee colony losses and declining honey bee colony health," the Bayer statement added.

"All new bee research involving bee health is welcome and great care should be taken to avoid sweeping, unsupportable conclusions based on artificial and unrealistic study parameters that are wildly inconsistent with actual field conditions and insecticide use," Bayer officials added.


Lu's study was prompted by the hypothesis that many seed treatments for commercial crops include neonicotinoids that will become systemic throughout the plant after germination. He suspects that the chemical or its breakdown products get into corn kernels and thereby into corn syrup.

Besides treated seed or corn syrup, bees may be affected by landing on crops like apples, pears, broccoli and cauliflower that are treated with the pesticide.

Some bee researchers don't buy that the neonicotinoids alone are to blame for CCD or that the Massachusetts study really replicated the disorder of bee hives.

One Oregon State researcher said the research fails to show how much of the insecticide the bees had actually carried into the hive.

Ongoing research by various studies shows that bees may not be solely affected by one culprit insecticide.

A 2010 study measured 121 different pesticides or their breakdown products that had been taken from bees, their pollen or wax or other hive materials, though average numbers of findings in each of those materials was under 10 pesticides found.

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