Beekeepers use a bee smoker to calm bee colonies before transferring them to another crop after pollinating a blueberry field near Columbia Falls, Maine June 23, 2014.© REUTERS/Adrees Latif Beekeepers use a bee smoker to calm bee colonies before transferring them to another crop after pollinating a blueberry field near Columbia Falls, Maine June 23, 2014. An insecticide widely used on grains, vegetables, fruit and other crops nationwide threatens honeybees, federal environmental regulators said in a decision that could lend impetus to efforts to ban the chemical.The Environmental Protection Agency said Wednesday that imidacloprid, a nicotine-imitating chemical found in at least 188 farm and household products in California, “potentially poses risk to hives when the pesticide comes in contact with certain crops that attract pollinators.”California farmers applied nearly 100 tons of the chemical in 2011, the same year the state Department of Pesticide Regulation found that residues of the compound in agricultural runoff exceeded an EPA threshold for toxicity to aquatic life in 19 percent of samples taken.

The EPA is to complete a fuller assessment of all risks posed by the chemical by the end of the year, after which it could tighten controls over the pesticide, originally manufactured by Bayer CropScience.

The assessment, done in collaboration with California and Canada, is the first of four expected to examine the potential danger to bees of a class of pesticides known as neonicotinoids.

Honeybees are used to pollinate crucial food crops and contribute about $14 billion in value to the agricultural economy nationwide.

In California, the almond industry is completely dependent on nearly 1 million commercial hives brought in to pollinate about 400,000 acres of trees.

Other crops that depend strongly on commercial honeybee colonies include oranges and grapefruits, blueberries, cherries, alfalfa, apples, avocados, cucumbers, onions, cantaloupe, cranberries, pumpkins and sunflowers.

Several studies have linked high levels of neonicotinoids to decreased foraging, failures of queens, breakdowns in hive communication and other colony-threatening behavior. Last year, however, a study that used levels of the pesticide that reflect actual farm conditions found no ill effects on bee colonies.

Exposure to multiple pesticides, natural pathogens and the stress of commercial management has been implicated in a catastrophic collapse of bee colonies that began a decade ago. Although full-scale colony collapses have largely abated over the last several years, bee mortality remains above normal.

The EPA and its research partners weighed evidence from several hundred scientific studies, according to Charlotte Fadipe, spokeswoman for the California Department of Pesticide Regulation.

The agency concluded that chemical residues of more than 25 parts per billion likely will harm bees.

Last year, the agency halted approval of any new outdoor uses of neonicotinoid pesticides until it completes a full risk assessment, expected by the end of this year. It also has proposed banning use of any pesticide found to be toxic to bees while crops are in bloom and commercial colonies are present.

Officials from Bayer CropScience were not immediately available for comment.

The Center for Biological Diversity, an environmental advocacy group, chided the EPA for not broadening its investigation beyond the honeybee to the more than 4,000 wild bee species, and to other pollinators, including butterflies and bats.

“You can’t claim to do a ‘pollinator risk assessment’ and really only look at one pollinator, the honeybee,” said Lori Ann Burd, Environmental Health director of the group. “That’s not only cheating on the purpose of this work but also cheating the native bees, birds, butterflies and other species threatened by this pesticide. In fact, many of these other pollinators are even more vulnerable to neonicotinoids than honeybees.”