The Oregon Department of Agriculture has restricted the use of two insecticides to help protect pollinators, including honeybees.

The action comes after thousands of bumblebees were killed this summer with a misapplication of insecticides on European linden trees, according to a news release.

Shortly after, the state restricted the use of 18 pesticides that contained dinotefuran while it continued investigating the bumblebee deaths in Wilsonville and Hillsboro.

Beginning in 2014, Oregon will require a state-specific label on dinotefuran and imidacloprid products sold in the state that prohibits their application on linden, basswood or Tilia species.

Dinotefuran, a neonicotinoid insecticide, is the active ingredient in several insecticides, including Venom, Safari 2 G and Safari 20 SG from Valent U.S.A.; and Scorpion 35SL from Gowan Co.

Imidacloprid, also a neonicotinoid, is the active ingredient in Admire Pro from Bayer CropSciences and several other off-patent products.

Apparently, the trees' natural toxicity combined with the pesticide contributed to the bumblebee deaths.

The state's temporary restriction on the 18 pesticides will expire in December.

The investigation into the pollinator deaths also is expected to be completed by mid-December.

Applicators testing for their license or seeking re-certification will receive additional education on pollinator protection.

Agriculture department Katy Coba also has sent a letter to the Environmental Protection Agency requesting additional evaluations of these active ingredients as well as other neonicotinoids. She also questioned whether use limitations on a national basis should be considered.

For more information about pollinator protection, visit the Oregon Department of Agriculture Pesticide Program's website.