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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

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 or 388-8583. 

©2007 Kalamazoo © 2007 Michigan Live. All Rights Reserved.


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