Published September 07, 2007
WASHINGTON – Scientific sleuths have a new suspect for what's been killing billions of honeybees: a virus previously unknown in the United States.
The scientists report using a novel genetic technique and old-fashioned statistics to identify Israeli acute paralysis virus as the latest potential culprit in the widespread deaths of worker bees, a phenomenon known as colony collapse disorder.
Next up are attempts to infect honeybees with the newfound virus to see if it's indeed a killer.
"At least we have a lead now we can begin to follow. We can use it as a marker and we can use it to investigate whether it does in fact cause disease," said Dr. W. Ian Lipkin, a Columbia University epidemiologist and co-author of the study.
Details appear this week in Science Express, the online edition of the journal Science.
Experts stressed that parasitic mites, pesticides and poor nutrition all remain in the lineup of suspects, as does the stress of travel.
Beekeepers shuffle bees around the nation throughout the year so they can pollinate crops as they come into bloom.
The newfound virus may prove to have added nothing more than insult to the injuries bees already suffer, said several experts unconnected to the study.
"This may be a piece or a couple of pieces of the puzzle, but I certainly don't think it is the whole thing," said Jerry Hayes, chief of the apiary section of the Florida department of agriculture.
Still, surveys of honeybees from decimated colonies turned up traces of the virus nearly every time; bees untouched by the phenomenon were virtually free of it. That means finding the virus should be a red flag that a hive is at risk and merits being quarantined, scientists said.
"The authors themselves recognize it's not a slam dunk, it's correlative. But it's certainly more than a smoking gun — more like a smoking arsenal. It's very compelling," said May Berenbaum, a University of Illinois at Urbana-Champaign entomologist.
The mysterious deaths have struck between 50 percent and 90 percent of commercial honeybee hives in the United States, sowing fears about the effects on the more than 90 crops that rely on bees to pollinate them.
Scientists previously have found blasting emptied hives with radiation apparently kills whatever infectious agent that causes the disorder.
That has focused their attention on viruses, bacteria and the like, to the exclusion of other noninfectious phenomena, such as cell phone interference, also proposed as culprits.
The earliest reports of colony collapse disorder date to 2004, the same year the virus was first 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.
Australia is now being eyed as a potential source of the virus. That could turn out to be an ironic twist, since the Australian imports were meant to bolster, not further damage, U.S. bee populations devastated by another scourge, the varroa mite.
Meanwhile, officials are discussing reinstating the ban, said the Agriculture Department's top bee scientist, Jeff Pettis.
In the new study, a team of nearly two dozen scientists used the genetic sequencing equivalent of a dragnet to round up suspects. The technique, called pyrosequencing, generates a list of the full repertoire of genes in bees they examined from U.S. hives and directly imported from Australia.
By separating out the bee genes and then comparing the leftover genetic sequences to others detailed in public databases — a move akin to running a suspect's fingerprints — the scientists could pick out every fungus, bacterium, parasite and virus harbored by the bees.
They then looked for each pathogen in bees collected from normal hives and others affected by colony collapse disorder. That statistical comparison showed Israeli acute paralysis virus was strongly associated with the disorder.
The technique is a model for investigating outbreaks of infectious diseases in people too, since it can rapidly pinpoint likely causes, Lipkin said.
Sela, a Hebrew University of Jerusalem professor, said he will collaborate with U.S. scientists on studying how and why the bee virus may be fatal.
Preliminary research shows some bees can integrate genetic information from the virus into their own genomes, apparently giving them resistance, Sela said in a telephone interview.
Sela added that about 30 percent of the bees he's examined had done so.
Those naturally "transgenic" honeybees theoretically could be propagated to create stocks of virus-resistant insects, Lipkin said.