An insecticide is suspected of causing a "colony collapse'' disorder that has killed millions of honeybees worldwide and up to half of the 2.5 million colonies in the United States.
The chief suspect, say many scientists, is imidacloprid, the most commonly used insecticide on the planet.
Honeybees come into contact with pesticides because they are needed to pollinate scores of crops, including apples, cherries, blueberries and other crops in southwestern Michigan.
The die-off has been a major concern for farmers and scientists, who have been looking into potential causes, from diseases and parasites to pesticides.
A member of a class of pesticides called neonicotinoids, imidacloprid is a synthetic derivative of nicotine and works by impairing the central nervous system of insects, causing their neurons to fire uncontrollably and eventually leading to muscle paralysis and death. The potent chemical can be sprayed on plants or coated on seeds, which then release the insecticide through the plants as they grow.
Research has shown that in sublethal doses imidacloprid and other neonicotinoids can impair honeybees' memory and learning, as well as their motor activity and navigation. Recent studies have reported "anomalous flying behavior'' in imidacloprid-treated bees, in which the workaholic insects simply fall to the grass or appear unable to fly toward the hive.
Imidacloprid was used on just a few specialty crops when it first came out, but its use has become much more widespread because of its effectiveness against a wide range of pests, said Mark Longstroth, Michigan State University Extension's district educator for fruit in southwestern Michigan. It is also used by homeowners because "it's very safe for the mammalian system,'' he said.
Longstroth hasn't reviewed data on how imidacloprid is suspected to affect the honeybees, but he said implicating the chemical as the colony collapse culprit sounds plausible. Launched in 1994 by Bayer AG, the German health-care and chemical company, imidacloprid is sold under various brand names, such as Admire, Advantage, Gaucho, Merit, Premise and Provado. It also is manufactured for use on flowers, lawns, trees, golf courses and even pets in the form of flea collars. The product list soon could grow even longer.
Last fall, Bayer announced findings indicating imidacloprid's ability to promote plant health even in the absence of infestation. "These things (imidacloprid insecticides) do a great job on termites, fleas, ticks, but people forget honeybees are insects, too,'' said Jerry Hayes, president of the Apirary Inspectors of America and an entomologist with the Florida Department of Agriculture.
In the mid-1990s, imidacloprid was implicated in a massive bee die-off in France in which a third of the country's 1.5 million registered hives were lost. After beekeepers protested, imidacloprid was banned for several uses, including treatment of sunflowers and corn seed.
The possibility that neonicotinoids are at the heart of the bee die-off implies a far more complex problem because of their widespread use. Every year these chemicals are applied to hundreds of millions of acres of agricultural lands, gardens, golf courses and public and private lawns across the United States. Their use on major crops nearly tripled between 1964 and 1982, from 233 million pounds to 612 million pounds of active ingredients. And since then, their use has exploded. By 1999, the U.S. Environmental Protection Agency reported 5 billion pounds of pesticides used on U.S. crops, forests, lawns, flowers, homes and buildings.
Because of imidacloprid's emergence as a primary player in pest management, a painful paradox has developed in the recent debate. Neonicotinoids are needed by farmers and growers to maintain the health of crops, many of which also require pollination by honeybees. "Neonicotinoids are now the best aphid insecticide we have,'' said Peter Shearer, a specialist in fruit tree entomology with the Rutgers Agricultural and Extension Center in Bridgeton, N.J. "It's very important to our pests that have shown resistance to other chemicals. It's very important to eggplants, potatoes, tomatoes.''
Shearer notes that apple farmers, for instance, don't use Provado, which has imidacloprid as an active ingredient, until after bees used for pollination are removed from the orchards. "So it doesn't seem to be a logical route of bee die-off,'' he said. "It would have to last 11 months.'' However, Shearer also acknowledges that some published studies indicate that imidacloprid can persist on both vegetation and in the soil for weeks, months and perhaps years.
Some U.S. entomologists who recently have been analyzing dead bees have found a remarkably high number of viruses and fungal diseases in the carcasses, leading them to suspect there may be other culprits besides neonicotinoids. "I don't think there is one smoking gun,'' Hayes said. "When neonicotinoids are used on termites, they can't remember how to get home, they stop eating, and then the fungus takes over and kills them. That's one of the ways imidacloprid works on termites -- it makes them vulnerable to other natural organisms. So if you look at what's happening to honeybees, that's pretty scary.''
Gazette staff writer Paula Davis contributed to this report.
She can be reached at firstname.lastname@example.org or 388-8583.
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Widely-Used Bayer Pesticide Blamed for Mass Deaths of Honeybees
Suspect in bee die-off: Insecticide
Widely used bug spray may be behind deaths of millions of bees
By Amy Ellis Nutt
Newhouse News Service, May 23, 2007
Straight to the Source