Commercial beekeepers and environmental organizations are asking federal regulators to suspend use of a pesticide they say harms honeybees.
The groups filed a petition Wednesday in Fresno California, urging the U.S. Environmental Protection Agency to ban the insecticide clothianidin.
Beekeepers and some scientists say the chemical contributes to colony collapse disorder by weakening bees' immune systems and making them more susceptible to pathogens.
Bees pollinate about a third of U.S. crops.
The EPA registered clothianidin in 2003. The agency says the chemical poses less risk to workers and wildlife than alternatives.
While data show clothianidin is toxic to honeybees, the EPA says there's no proven link to bee colony die-offs from exposure to the chemical.