WASHINGTON - The mysterious deaths of billions of honeybees since 2006 that have harmed the agricultural industry may be caused by a common fungus and a previously unknown virus, University of Montana researchers say.
The virus, Invertebrate Iridescent Virus, or IIV6, seems to work together with the Nosema fungus to kill the bees, said the researchers, Colin Henderson and Jerry Bromenshenk, in findings published in the online science journal PLoS ONE. The bee disease known as Colony Collapse Disorder first appeared in 2006 and causes entire hives to die off without explanation.
Honeybees pollinate $15 billion of U.s. crops each year, according to the Department of Agriculture, and companies from General Mills and Clorox use pollinated crops in their products. Scientists had looked toward viruses and fungal infections as a cause of the disorder. The disease has been reported in at least 35 states and been found in Europe, Asia and South America.
"We have a strong suspect, I'm convinced we have what it is," Henderson, an associate professor at the university's College of Technology, said in a telephone interview.
Since the first outbreak in 2006, the disorder has showed up in 26 percent to 36 percent of hives each year, according to a survey released in April by the Department of Agriculture. The primary indication of colony collapse is whether hives were found empty. The disorder is characterized by a massive flight of bees, which don't return to their hives to die.
Bees are essential for the health of pollinator-dependent crops such as almonds and blueberries. Fruit-pollinated products are found in items such as Haagen-Dazs ice cream from Minneapolis-based General Mills. Lip balm made by Burt's Bees Inc., a unit of Clorox, contains wax from the honeycombs of beehives.
Henderson and Bromenshenk began looking into the cause of the bee disorder in 2006, when the first cases appeared. They found Nosema, a single-celled fungus that was already well known, and uncovered a suspicious DNA virus, IIV6, that "nobody had looked for," Henderson said.
"That pattern of those two showed up about 100 percent in the first infected colonies that we found," Henderson said. When a second outbreak of the mysterious illness hit, the scientists collected more samples, and again the virus and the fungus appeared in the dead bees.
Then came more evidence. One of the bee colonies kept by the University of Montana researchers got the disease, and for the first time, scientists we were able to track the malady from beginning to end, Henderson said.
The tool to dig up the surprise virus from the dead bees came from a U.S. Department of Defense program meant to monitor disease outbreaks in people, specifically from biological weapons.
The Defense Department technology essentially took ground up bee parts and pulled out chains of proteins, some of which may have been the virus infecting the bees. Henderson and Bromenshenk compared the discoveries against a giant database of known proteins funded by the National Science Foundation.
"We just looked for everything," Henderson said. What they found was IIV6, a virus that was common in moths though it wasn't known to exist in bees.
Having identified the virus and the fungus, the researchers tested bees in the lab. First they infected the bees with the fungus alone, and some died, though not as many as with Colony Collapse Disorder. Then they infected some with just the virus, with the same result. When the combination of virus and fungus was used, the results resembled the deadly disorder that had been wiping out hives across the country, the researchers said.
The next step will be to test the theory in the field to see if it proves true, Henderson said.
"The real closure of the circle for us is to take the two pathogens to inoculate a colony, see it collapse, then pull out the pathogens again," he said. That will allow scientists to be sure they have identified the cause, he said.
"We're eight-tenths of the way there, in my opinion," Henderson said.