Scientists have found a virus associated with the destruction of a large fraction of American commercial bee colonies, but they have not been able to prove that it is the cause of the mysterious disease that has wreaked havoc on the bee industry.
The virus, Israeli acute paralysis, may have been introduced by bees from Australia whose importation was first permitted in 2004, about the same time that the disease, Colony Collapse Disorder, or CCD, began appearing in the United States.
Australian bees do not suffer from the disorder, leading researchers to speculate that the virus interacts with chemicals in the environment or with another infectious agent, such as the varroa mite, which is not common in Australia.
Experiments are underway to determine which combination of virus and chemical or infectious agent might cause the disease, an answer that may come this year. Researchers are also examining archived bee specimens to determine whether the virus was present before 2004.
"Our results indicate that [the virus] is a significant marker" for the disorder, said Dr. W. Ian Lipkin of Columbia University's Mailman School of Public Health, a co-author of the report published online Thursday by the journal Science. "The next step is to ascertain whether [the virus], alone or in concert with other factors, can induce [the disorder] in healthy bees."
Entomologist May Berenbaum of the University of Illinois said the find was "compelling."
But researchers from the Army's Edgewood Chemical Biological Center in Maryland cautioned that they had unpublished results in which the Israeli virus had been found in colonies without the disorder.
Although the United States has experienced other bee die-offs, the latest episode has been one of the worst, affecting about 23% of beekeepers. Typically, 50% to 90% of a keeper's colonies are affected as worker bees fail to return to their hives, leaving the queen with a handful of newborns.
Agricultural experts view the deaths with alarm because bees are required to pollinate about a third of the nation's food crops, including almonds, cherries, pears, blueberries, strawberries and pumpkins.
The number of bee colonies in the country is about 2.5 million, half as many as in the 1940s and '50s.
"We don't have a great deal of buffer" for dealing with bee losses, said entomologist Diana Cox-Foster of Pennsylvania State University.
