RALEIGH, N.C. — Bayer CropScience is facing scrutiny because of the effect one of its best-selling pesticides has had on honeybees.

A German prosecutor is investigating Werner Wenning , Bayer's chairman, and Friedrich Berschauer , the head of Bayer CropScience , after critics alleged that they knowingly polluted the environment.

The investigation was triggered by an Aug. 13 complaint filed by German beekeepers and consumer protection advocates, a Coalition against Bayer Dangers spokesman, Philipp Mimkes, said Monday.

The complaint is part of efforts by groups on both sides of the Atlantic to determine how much Bayer CropScience knows about the part that clothianidin may have played in the death of millions of honeybees.

Bayer CropScience , which has its U.S. headquarters in Research Triangle Park , said field studies have shown that bees' exposure to the pesticide is minimal or nonexistent if the chemical is used properly.

Clothianidin and related pesticides generated about $1 billion of Bayer CropScience's $8.6 billion in global sales last year. The coalition is demanding that the company withdraw all of the pesticides.

"We're suspecting that Bayer submitted flawed studies to play down the risks of pesticide residues in treated plants," said Harro Schultze , the coalition's attorney.

"Bayer's ... management has to be called to account, since the risks ... have now been known for more than 10 years."

Under German law, a criminal investigation could lead to a search of Bayer offices, Mimkes said.

On the other side of the Atlantic, the Natural Resources Defense Council is pressing for research information on clothianidin.

The U.S. Environmental Protection Agency approved the pesticide in 2003 under the condition that Bayer submit additional data. A lawsuit, which the environmental group filed Aug. 19 in federal court in Washington , accuses the EPA of hiding the honeybee data.