The researchers also tested apparently healthy bees imported from Australia, as well as royal jelly—a substance fed to bee larvae to start up new colonies—that was imported from China.
The Australian samples showed signs of IAPV. All of the U.S. operations infected with IAPV had either imported bees from Australia—a practice that began in 2004—or stored their hives close to operations with Australian bees.
An estimated 14 billion U.S. dollars in agricultural crops in the United States are dependent on bee pollination.
The CCD epidemic has affected between 50 and 90 percent of commercial honeybee colonies in the U.S.
Other researchers have found no Australian connection or even a link between IAPV and the bee collapse.
A team led by Jerry Bromenshenk of Bee Alert Technology in Missoula, Montana, has been working with the U.S. Army's Edgewood Chemical Biological Center in Maryland.
"We don't find a common denominator virus across the CCD colonies, whether they're U.S. or Australian colonies," Bromenshenk said.
The Army's research has spotted more than a dozen viruses, Bromenshenk said.
"It seems a bit premature to pick out a specific pathogen or emphasize a link to Australian bees," he said.
Experts also point out that CCD-affected hives tend to develop many secondary diseases, and that IAPV infection could be a consequence rather than a cause of the disorder.
A Good Lead
The study authors acknowledge that IAPV is unlikely to be the sole cause of the disease.
"The research gives us a very good lead to follow, but we do not believe IAPV is acting alone," said study co-author Jeffery Pettis, research leader of the Bee Research Laboratory of the U.S. Department of Agriculture.
The researchers believe there may be certain triggers—from pesticides to nutritional stresses—that may play a part in the disease.
Diana Cox-Foster, an entomologist at Pennsylvania State University, is the lead author on the new study.
"IAPV is a relatively recent discovery," she said. "We don't know how it's being transmitted, how it's moving through colonies, and what symptoms one would see at different levels of prevalence."
Cox-Foster said there is no evidence to back up some of the more unusual explanations some have proposed to explain the epidemic, such as cell phone radiation.
So far there is no way for beekeepers to determine if their colonies are affected by the virus, and no treatment.
"For now, we have to rely on beekeepers continuing to manage nutrition and parasitic mites," said Pettis of the Bee Research Laboratory, "and try to keep their bees as healthy as possible."
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