A controversial new study of honeybee deaths has deepened a bitter dispute over whether the developed world’s most popular pesticides are causing an ecological catastrophe.
Researchers led by biologist Chensheng Lu of Harvard University report a direct link between hive health and dietary exposure to imidacloprid, a so-called neonicotinoid pesticide linked to colony collapse disorder, the mysterious and massive die-off of bees across North America and Europe.
The study isn’t without critics, who say doses used in the study may be unrealistically high. But the level of a realistic dose is also a matter of controversy, and even critics say the findings are troubling.
“Our result replicates colony collapse disorder as a result of pesticide exposures,” said Lu, who specializes in environmental exposures to pesticides. “We need to look at our agriculture policy and see if what we’re doing now is sustainable.”
Developed in the 1990s as a relatively less-toxic alternative to pesticides that seriously harmed human health, neonicotinoids soon became the world’s fastest-growing pesticide class and an integral part of industrial agricultural strategy. In the United States alone, neonicotinoid-treated corn now covers a total area slightly smaller than the state of Montana.
Like earlier pesticides, neonicotinoids disrupt insects’ central nervous systems. But unlike earlier pesticides, which affected insects during and immediately after spraying, neonicotinoids spread through the vascular tissues of plants. They’re toxic through entire growing seasons, including flowering times when bees consume their pollen.
The first reports of colony collapse disorder came in the mid-2000s from commercial beekeepers, who depending on region have experienced colony losses ranging from 30 to 90 percent. Commercial pollination costs have since skyrocketed, and as wild bees are also afflicted, even naturally occurring pollination is threatened.
Measuring bee declines, however, proved much easier than explaining them. Among a lineup of potential culprits including fungus, mites, viruses, bacteria and pesticides, studies failed to find an obvious, smoking-gun cause — but, piece by piece, evidence against neonicotinoids has steadily accumulated.
Honeybees are clearly exposed to them throughout the year and through multiple environmental routes. At certain times, especially in spring, death often follows exposure, and even non-lethal exposures may disrupt bee learning and navigation. Neonicotinoids also appear to make bees especially vulnerable to certain parasites and may interact similarly with other stressors.
Some European countries, including France, Germany and Italy, have even banned neonicotinoids, though pesticide companies vehemently defend their ecological safety and say concerns are based on inconclusive and premature science.
Lu’s study, released April 5 and scheduled for publication in the June Bulletin of Insectology, attempts to replicate the life history of commercial bees, which are often fed dietary supplements of high-fructose corn syrup that may contain neonicotinoid residues that survive processing.
“We tried to mimic commercial beekeepers’ practices. I believe one reason that commercial beekeepers are experiencing the most severe colony collapse disorder is because of the link between high-fructose corn syrup and neonicotinoids,” Lu said.
In the spring of 2010, the researchers set up four groups of commercially purchased colonies. Each contained five hives, and during the summer months were fed a diet containing either no imidacloprid, what Lu considered a small dose of 20 parts per billion, or a much higher dose of 400 parts per billion.
Colony collapse disorder is characterized in part by bees abandoning their hives during winter, and that’s precisely what Lu’s team reported in 15 of 16 imidacloprid-receiving hives. While other colony collapse disorder symptoms, such as queens that stay in the hive while workers flee, were not reported, Lu considers the experimentally induced collapse to be realistic.
Reaction to the study was swift and varied.
Bayer, the chemical and pharmaceutical giant that manufactures imidacloprid, issued a formal statement denouncing the findings as “spectacularly incorrect” and “based on artificial and unrealistic study parameters that are wildly inconsistent with actual field conditions insecticide use.”
But Jeffery Pettis, a bee biologist at the United States Department of Agriculture, called the results “tantalizing but not conclusive.” With only four colonies used per dose level, the study’s statistical significance is limited, “but I would love to see this study replicated such that the trends … they observed could be actually validated,” wrote Pettis in an email.
Among Bayer’s criticisms is that imidacloprid, a first-generation neonicotinoid, is little-used in the United States. It’s largely been replaced by newer formulations — but these, said pesticide expert Charles Benbrook of The Organic Center, an organic food research consultancy, are chemically similar to imidacloprid.
“Virtually all our corn seed has been treated with a very similar neonicotinoid,” said Benbrook. If the study had been conducted with clothianidin, another controversial neonicotinoid, “they’d almost certainly have found the same thing.”
According to Bayer, “analysis from actual field grown corn samples have shown no detectable imidacloprid residues” in high-fructose corn syrup. But Benbrook said that extensive testing by the Organic Center found traces of imidacloprid, but they were impossible to quantify.“It’s very difficult to test for this particular chemical in high-fructose corn syrup. A lot of labs have spent lots of time trying to do it, but high-fructose corn syrup is a very sticky, dense matrix that basically gums up the testing machines,” said Benbrook. “That’s why relatively little is known about imidacloprid in high-fructose corn syrup.” ….
The document, which was leaked to a Colorado beekeeper, shows that the EPA has ignored warnings about the use of clothianidin, a pesticide produced by Bayer that mainly is used to pre-treat corn seeds. The pesticide scooped up $262 million in sales in 2009 by farmers, who also use the substance on canola, soy, sugar beets, sunflowers, and wheat, according to Grist.
The leaked document (PDF) was put out in response to Bayer’s request to approve use of the pesticide on cotton and mustard. The document invalidates a prior Bayer study that justified the registration of clothianidin on the basis of its safety to honeybees:
Clothianidin’s major risk concern is to nontarget insects (that is, honey bees). Clothianidin is a neonicotinoid insecticide that is both persistent and systemic. Acute toxicity studies to honey bees show that clothianidin is highly toxic on both a contact and an oral basis. Although EFED does not conduct RQ based risk assessments on non-target insects, information from standard tests and field studies, as well as incident reports involving other neonicotinoids insecticides (e.g., imidacloprid) suggest the potential for long-term toxic risk to honey bees and other beneficial insects.
The entire 101-page memo is damning (and worth a read). But the opinion of EPA scientists apparently isn’t enough for the agency, which is allowing clothianidin to keep its registration.
Suspicions about clothianidin aren’t new; the EPA’s Environmental Fate and Effects Division (EFAD) first expressed concern when the pesticide was introduced, in 2003, about the “possibility of toxic exposure to nontarget pollinators [e.g., honeybees] through the translocation of clothianidin residues that result from seed treatment.” Clothianidin was still allowed on the market while Bayer worked on a botched toxicity study [PDF], in which test and control fields were planted as close as 968 feet apart.
Clothianidin has already been banned by Germany, France, Italy, and Slovenia for its toxic effects. So why won’t the EPA follow? The answer probably has something to do with the American affinity for corn products. But without honey bees, our entire food supply is in trouble. …