Thursday, May 24, 2007
By Amy Ellis Nutt
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.