Insecticides taking toll on honeybees
When I first wrote about the mysterious epidemic of honeybee mortality in early 2007, the phenomenon had just been termed colony collapse disorder, or CCD. Scientists were at a loss to explain why bees were wandering away from hives and not returning. Commercial beekeepers have seen average population losses of about 30 percent each year since 2006, and mounting evidence indicates a class of insecticides known as neonicotinoids might be at least partially responsible for the phenomenon.
Because they are systemic insecticides, vascular systems of both plants treated with the product and those that grow from seeds treated with neonicotinoids are suffused with it, which means the insecticide is "expressed" in all parts of the plant, from its roots, stem and leaves to its nectar and pollen. These pesticides act as neurotoxins, and insects that dine on any part of treated plants are subject to paralysis and death.
According to the U.S. Environmental Protection Agency, the agency responsible for the regulation of pesticides, neonicotinoids account for more than 20 percent of the worldwide insecticide market.
In late 2010, a document prepared by the EPA in response to a request by the parent company of the neonicotinoid clothianidin — originally approved in 2003 — that it be approved for use on some additional crops was leaked to a Colorado beekeeper.
The EPA report said "clothianidin's major risk concern is to nontarget insects (that is, honeybees)." It went on to say, "Acute toxicity studies to honey bees show that clothianidin is highly toxic on both a contact and an oral basis. 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 report also outlined the potential toxic impact to aquatic species upon entrance into waterways and said: "The proposed application rates and uses also pose an acute and chronic risk to small birds and mammals when clothianidin treated seeds are applied with low efficiency or no incorporation methods."
In response, six national groups affiliated with beekeeping and what I'll call pesticide nonproliferation wrote to the EPA demanding a "stop-use order" on clothianidin. And even though its own scientists' findings questioned its use, the EPA's patronizing response refused to budge, saying a review is planned in the near future, though several conflicting dates for the scheduling of that study exist.
Last month, Purdue University released findings from research on the routes of pesticide exposure that supports the role of neonicotinoids in honeybee deaths.
The U.S. Department of Agriculture estimates the seed corn used to plant virtually the entire U.S. corn crop — more than 90 million acres — is treated with neonicotinoids such as clothianidin and thiamethoxam. About half of soybean seeds also are treated.
These insecticide coatings are sticky, and talc is mixed with the seeds to keep them flowing freely. The study found that the large amounts of insecticide-laced talc being released into the environment in the process is more toxic — up to about 700,000 times the lethal contact dose for a bee — than what the little pollinators pick up from corn pollen.
"This material is so concentrated that even small amounts landing on flowering plants around a field can kill foragers or be transported to the hive in contaminated pollen," said Christian Krupke, associate professor of entomology at Purdue and a co-author of the findings.
Bees that do not die from the insecticide might still suffer from the cumulative sublethal effects from exposure that directly correspond to the symptoms of CCD: a loss of homing ability and neurobehavioral and immune system disruptions.
The problem is exacerbated by the fact clothianidin has a soil half-life of as long as 19 years in heavy soils and more than a year in lighter soils, so plants that grow there will continue to express the insecticide.
Clothianidin was banned in Germany, the country of its origin, in 2008 and also in France, Italy and Slovenia. The release of the Purdue study has beekeepers, honey producers and environmental groups again calling on the EPA to ban it.
Please be aware that neonicotinoids also are present in products for use by landscapers and home gardeners. Check labels before you open your wallet. Others not mentioned so far are acetamiprid, dinotefuran and thiacloprid.
Bees pollinate more than 70 of the 100 crops that provide 90 percent of the world's food.