Imidacloprid effects on bees

For the South American cattle herder see gaucho.

Gaucho is the trade name for a systemic insecticide containing the active ingredient imidacloprid. It is produced by the chemical firm Bayer AG.

Gaucho has a mode of action where it is applied to the seed before sowing, or the leaf of the plant. It diffuses in the plant vascular system. Insects ingest it by sucking the plant fluids. Imidacloprid is a very toxic insecticide (very quick and effective on insects), and is highly persistant in the crop. It is widely used on sunflowers as well as corn.

Gaucho use is highly controversial in France, where its use is believed to be linked to high losses in bees. According to the National Union of French Beekeepers, the number of hives in France has plummeted to one million in 2003, from 1.45 million in 1996. French beekeepers claim that Gaucho, as a seed treatment for sunflowers has killed many bees and caused a significant drop in honey production. Some request that systemic insecticides uses are withdrawn from crops where bees may be affected, while others call for a complete ban on Gaucho use.

The French government used the precautionary principle and decided to withdraw the use of imidacloprid as a sunflower seed treatment in 1999 and renewed the ban in 2001. In 2003, agricultural Minister Jean Glavany extended the suspension on the use of Gaucho on sunflower seeds and called for a full study. However, a significant drop in bee individuals are still observed. Some suggest that the bee colony losses could also be due to the use of imidacloprid on corn as well, or by the replacement of it by another systemic insecticide called Fipronil. Indeed in may 2003, the DGAL (Direction Générale de l'Alimentation du ministère de l'Agriculture ) indicated death of bees observed in the south of the country had been caused by accute toxicity by Fipronil (as the active chemical in the systemic insecticide called Regent), while it was recognised Gaucho had no responsability in the bees death. Some national field studies are currently under way (2003) to assert the responsability of Gaucho.

Bayer scientists denied the product was responsible for the colonies death in a meeting in 2000. A 1998 report of the University of Bonn also concluded that the French bee loss was not linked to imidacloprid but to a viral disease or a spiroplasm in bees which produces similar symptoms.

Bayer now agree that the insecticide may cause disorientation of bees at levels above 20 parts per billion of the active ingredient. However recent studies by researchers at the Institut National de la Recherche Agronomique (INRA) suggest that bee behaviour is affected at levels between 3-16 ppb or possibly even 0.5 ppb.

In May 2003, Bayer also brought a judicial case against one of the leaders of the French association of beekeepers for disparagement of the chemical Gaucho. The action was dismissed by the judge.

A similar battle is occurring in Nova Scotia, where beekeepers are accusing Gaucho used on potatoes for massive losses of bees needed for blueberry pollination.