Beekeeping groups have filed a challenge against the Environmental Protection Agency over its approval of the pesticide sulfoxaflor, which is highly toxic to honeybees.

Sulfoxaflor, marketed by Dow Chemical under the brand names Closer and Transform, belongs to the Insecticide Resistance Action Committee's Group 4. This is the same group to which neonicotinoids belong.

But sulfoxaflor belongs to the 4C subclass—different than the subclass 4A, which includes neonicotinoids.

The groups have said the pesticide poses a threat to not just honeybees but other pollinators, and that the EPA violated the Federal Insecticide, Fungicide and Rodenticide Act in registering the insecticide, according to a news release.

In an e-mail, Garry Hamlin, Dow media relations manager, said, "Sulfoxaflor is less toxic to bees and less persistent in the environment than many of the insecticides that farmers are using now. EPA registered sulfoxaflor with the understanding that it would displace older products posing greater risk to bees."

The groups also claim that the tests conducted by Dow as part of the registration didn't accurately measure the chemical's effects on pollinators.

The groups include the Pollinator Stewardship Council (formerly the National Pollinator Defense Fund), national Honey Bee Advisory Board, American Honey Producers Association, the American Beekeeping Federation, and beekeepers Bret Adee, Jeff Anderson and Thomas R. Smith. They are being represented by Earthjustice.

The suit was filed in the Court of Appeals for the Ninth Circuit in San Francisco.