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Virus-Fungus Combo May Contribute to Honeybee Die-Off

Nearly four years after a mysterious die-off began decimating honeybee populations across the United States, researchers believe they may have a lead on a culprit — or rather, two culprits. A virus and a fungus working together may be behind “colony collapse disorder,” according to a study by a team of academic and military scientists, published this week in the journal Public Library of Science One.

Still, the researchers and others caution that much work remains to be done before scientists can say for certain what’s causing the die-off.

Colony Collapse Disorder, or CCD, first came to the public’s attention in late 2006, baffling beekeepers and scientists. In colonies around the country, bees would simply disappear — flying off and dying far from the hive. Such disappearances had been seen before, but no one knew why the number had ramped up so dramatically. Over the course of the next few years, researchers suggested many possibilities — mites, a virus, a fungus, pesticides and even some more far-fetched ideas such as radiation from cell phone towers. But none of the possibilities seemed fully able to account for the phenomenon.

The NewsHour reported on CCD in April 2007:

At the time, Jerry Bromenshenk, an entomologist at the University of Montana, was just beginning to investigate the collapsing colonies.

“There’s a whole variety of folks looking at whether it’s something new or something cyclic that we’ve seen before and it’s just particularly widespread this time around and unusually severe,” he told Spencer Michels. He added “It could be some type of disease pathogen, an unknown virus, for example, but there doesn’t seem to be anyway to slow it down, stop it, once it starts.”

Bromenshenk was one of the lead researchers on the new paper, which suggests that the disorder may be due to a combination of two things: A virus called invertebrate iridescent virus (IIV) and a fungus called Nosema ceranae, both of which target the guts of bees and could keep them from getting enough nutrition.

Bromenshenk and his colleagues catalogued the microbes in samples of dead bees from more than 40 colonies affected by CCD between 2006 and 2009, as well as control colonies that had not been touched by the disorder.

Other researchers had previously found evidence that both the IIV virus and the Nosema fungus might be connected to CCD, but the connection wasn’t definitive for either. Bromenshenk and his colleagues discovered that what the collapsed colonies in their study had in common was evidence of both the virus and the fungus — but not just one or the other alone.

But the scientists say they still don’t know how the two factors might work together.

“It’s chicken and egg in a sense — we don’t know which came first,” Bromenshenk told the New York Times. “They’re co-factors, that’s all we can say at the moment,” he said. “They’re both present in all these collapsed colonies.”

He also told the paper that more research is needed on how other factors such as heat and drought might factor in.

Dennis van Engelsdorp, an entomologist at Penn State University who also studies colony collapse disorder, says that the new study is very exciting. However, he says, to say that it has solved the mystery of CCD would be “overstating the case.”

“It’s validated our opinion that there are a lot of things going on,” in the disorder, he says. In other words, it’s not simply one virus, or other factor, causing the die-off. But, he says, it’s critical to figure out whether there is still some underlying cause — such as pesticides or nutrition — that could make the bees more susceptible to viruses and fungi.

“I think the really critical part here is that we have to figure out is: Are these viruses the cause or the consequence?” he says.

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