Tests on dead bees showed that 99% of those examined had a build-up of clothianidin. The chemical, produced by Bayer CropScience, a subsidiary of the German chemical giant Bayer, is sold in Europe under the trade name Poncho. It was applied to the seeds of sweetcorn planted along the Rhine this spring. The seeds are treated in advance of being planted or are sprayed while in the field.

The company says an application error by the seed company which failed to use the glue-like substance that sticks the pesticide to the seed, led to the chemical getting into the air.

Bayer spokesman Dr Julian Little told the BBC’s Farming Today that misapplication is highly unusual. “It is an extremely rare event and has not been seen anywhere else in Europe,�he said.

Clothianidin, like the other neonicotinoid pesticides that have been temporarily suspended in Germany, is a systemic chemical that works its way through a plant and attacks the nervous system of any insect it comes into contact with. According to the US Environmental Protection Agency it is “highly toxic�to honeybees.

This is not the first time that Bayer, one of the world’s leading pesticide manufacturers with sales of �.8bn (£4.6bn) in 2007, has been blamed for killing honeybees.

In the United States, a group of beekeepers from North Dakota is taking the company to court after losing thousands of honeybee colonies in 1995, during a period when oilseed rape in the area was treated with imidacloprid. A third of honeybees were killed by what has since been dubbed colony collapse disorder.

Bayer’s best selling pesticide, imidacloprid, sold under the name Gaucho in France, has been banned as a seed dressing for sunflowers in that country since 1999, after a third of French honeybees died following its widespread use. Five years later it was also banned as a sweetcorn treatment in France. A few months ago, the company’s application for clothianidin was rejected by French authorities.

Bayer has always maintained that imidacloprid is safe for bees if correctly applied. “Extensive internal and international scientific studies have confirmed that Gaucho does not present a hazard to bees,�said Utz Klages, a spokesman for Bayer CropScience.

Last year, Germany’s Green MEP, Hiltrud Breyer, tabled an emergency motion calling for this family of pesticides to be banned across Europe while their role in killing honeybees were thoroughly investigated. Her action follows calls for a ban from beekeeping associations and environmental organisations across Europe.

Philipp Mimkes, spokesman for the German-based Coalition Against Bayer Dangers, said: “We have been pointing out the risks of neonicotinoids for almost 10 years now. This proves without a doubt that the chemicals can come into contact with bees and kill them. These pesticides shouldn’t be on the market.�/FONT>