WASHINGTON — A new U.S. report blames a combination of problems for a mysterious and dramatic disappearance of honeybees across the country since 2006.
The multiple causes make it harder to do something about what's called colony collapse disorder, experts say. The disorder has caused as much as one-third of the nation's bees to just disappear each winter since 2006.
Bees, especially honeybees, are needed to pollinate crops, and they are crucial to the U.S. food supply. About $30 billion a year in agriculture depends on their health, said Sonny Ramaswamy with the U.S. Department of Agriculture.
The problem has also hit bee colonies in Europe, where regulators are considering a ban on a type of pesticides that some environmental groups blame for the bee collapse.
The report, issued Thursday by the USDA and the Environmental Protection Agency, is the result of a large conference of scientists that the government brought together last year to figure out what's going on.
The factors cited for the bees' disappearance include a parasitic mite, multiple viruses, bacteria, poor nutrition, genetics, habitat loss and pesticides. The report said the biggest culprit is the parasitic mite varroa destructor, calling it "the single most detrimental pest of honeybees."
The report also cites pesticides, but near the bottom of the list of factors. And federal officials and researchers advising them said the science doesn't justify a ban of the pesticides yet.
May Berenbaum, chairwoman of a major National Academy of Sciences study on the loss of pollinators, said the class of chemicals known as neonicotinoids hasn't been proven to be the sole culprit in the bee loss. In an interview, she said she was "extremely dubious" that banning the chemical would have any effect on bee health and that more than 100 different chemicals have been found in bee colonies.
Dave Gaulson of the University of Stirling in Scotland, who conducted a study last year that implicated the chemical, said he can't disagree with the overall conclusions of the U.S. government report. However, he said it could have emphasized pesticides more.
At a news conference with federal officials, Berenbaum said there's no single solution to the bee problem: "We're not really well equipped or even used to fighting on multiple fronts."
Besides making honey, honeybees pollinate more than 90 flowering crops. About one-third of the human diet comes from insect-pollinated plants, and the honeybee is responsible for 80 percent of that pollination.
"It affects virtually every American whether they realize it or not," said EPA acting administrator Bob Perciasepe.
Zac Browning, a fourth-generation commercial beekeeper, said the nation is "on the brink" of not having enough bees to pollinate its crops.
University of Maryland entomologist David Inouye, president-elect of the Ecological Society of America, was not part of the federal report. He said the problems in Europe and United States may be slightly different. In the U.S., bee hives are trucked from farm to farm to pollinate large tracts of land and that may help spread the parasites and disease, as well as add stress to the colonies, while in Europe they stay put, so those issues may not be as big a factor.