The EPA said the Bayer AG pesticide was approved in 2003 but bee colony collapse disorder first occurred in 2006. EPA spokesman Dale Kemery said beekeepers are finding empty hives instead of dead bees, which might be expected if CCD was related to a pesticide.

While the use of clothianidin has been halted in Germany due to concerns about its affect on bees, the EPA said recent bee deaths there appear to be related to inadvertent exposure to clothianidin and not CCD.

"Although pesticide exposure is one of four theoretical factors associated with CCD that the United States Department of Agriculture is researching, the facts in this case are not consistent with what is known about CCD," the agency said.

Bayer AG has said clothianidin won't harm bees if applied correctly.

Debra Edwards, the EPA's pesticide program director, was critical of a National Resources Defense Council lawsuit accusing the agency of failing to provide information about clothianidin. Edwards, in a letter on the EPA's Web site, said the agency requested more time to comply with the NRDC request.