BALTIMORE, Oct. 6 (UPI) -- A combination of a virus and a fungus could be responsible for colony collapse disorder, the mysterious syndrome killing U.S. honeybees, researchers say.

The findings, published in an online journal PLoS One, are the result of a joint effort by scientists at the Army's Edgewood Chemical Biological Center near Baltimore and the Bee Alert team at Montana State University and the University of Montana, The New York Times reported Wednesday.


They say the fungus-virus combination appears to be present in every killed colony, although neither agent can kill bees single-handed.

Colony collapse has killed 20 percent to 40 percent of honeybees in the United States since 2006 and has also devastated bee colonies in other countries, affecting both bee keepers and farmers. It is difficult to study because bees in afflicted colonies fly away, heading off in different directions.

Jerry Bromenshenk of the University of Montana said a lot of work needs to be done.

"It's chicken and egg in a sense -- we don't know which came first," he told the Times. "They're co-factors, that's all we can say at the moment. They're both present in all these collapsed colonies."