WASHINGTON -- Researchers on Thursday said recent die-offs in honeybee colonies, which are vital to many Central Valley crops, might be traced to a virus previously unknown in the United States.
The suspect is Israeli acute paralysis virus, a microbe discovered in Israel three years ago. A study said it might have acted in concert with other factors -- such as parasitic mites, weather extremes or pesticide poisoning -- to kill nearly a quarter of the nation's commercial colonies over the winter.
"At least we have a lead now we can begin to follow," said Dr. W. Ian Lipkin, a Columbia University epidemiologist and co-author of the study. "We can use it as a marker, and we can use it to investigate whether it does in fact cause disease."
The virus might have come to the United States by way of Australia, which exports colonies to U.S. beekeepers.
The study, by researchers at several universities and the U.S. Department of Agriculture, was published in the journal Science today and discussed at a Washington news conference Thursday.
Bee experts in the Northern San Joaquin Valley said they are taking the findings with caution.
"This gives us one potential avenue to follow," said Chris Heintz, who manages pollination research for the Modesto-based Almond Board of California. "It's not going to be just one stressor. It's multiple stressors acting together."
Valley almond growers are the nation's biggest user of commercial bee colonies in late winter. The insects spread the pollen that allows the blossoms to turn into the nuts that, in 2006, brought an estimated $833 million in gross income to growers in Stanislaus, Merced and San Joaquin counties.
Gene Brandi, a beekeeper based in Los Banos, said a viral cause is of concern because viruses can be spread by varroa mites, which invaded many beehives even before the recent die-offs.
"There are so many different things that adversely affect our bees that I think it would be difficult to say it's one thing," said Brandi, legislative chairman for the California State Beekeepers Association.
Crops OK, but there's a cost
Bee-dependent crops have managed to get through despite the shortage this year, he said. Almond growers benefited from the mild weather during the bloom, and the 2007 crop is expected to set a record.
Brandi said he lost about 40 percent of his bees over the winter but got back to normal by May, thanks to purchased bees. Growers, meanwhile, have seen the cost of renting hives more than double.
The die-off, formally known as colony collapse disorder, has been reported in many parts of the country. Some beekeepers have had little or no losses. Some have lost more than 90 percent.
The earliest reports of colony collapse disorder date to 2004, the same year the virus first was described by Israeli virologist Ilan Sela. That also was the year U.S. beekeepers began importing bees from Australia -- a practice that had been banned by the Honeybee Act of 1922.
Did imports cause problem?
Now, Australia is being eyed as a potential source of the virus. That could turn out to be an ironic twist, because the imports were meant to bolster U.S. bee populations devastated by the varroa mite.
In the study, the team of nearly two dozen scientists used a genetic sequencing technique that picked out every fungus, bacterium, parasite and virus in a sampling of colonies. They found the Israeli virus in nearly all of those affected by colony collapse disorder.
"The authors themselves recognize it's not a slam dunk, it's correlative," said May Berenbaum, an entomologist at the University of Illinois at Urbana-Champaign, who was not involved in the study. "But it's certainly more than a smoking gun -- more like a smoking arsenal. It's very compelling."
Bee staff writer John Holland can be reached at email@example.com or 578-2385.