A fungus that caused widespread loss of bee colonies in Europe and Asia may be playing a crucial role in the mysterious phenomenon known as Colony Collapse Disorder that is wiping out bees across the United States, UC San Francisco researchers said Wednesday.
Researchers have been struggling for months to explain the disorder, and the new findings provide the first solid evidence pointing to a potential cause.
But the results are "highly preliminary" and are from only a few hives from Le Grand in Merced County, UCSF biochemist Joe DeRisi said. "We don't want to give anybody the impression that this thing has been solved."
Other researchers said Wednesday that they too had found the fungus, a single-celled parasite called Nosema ceranae, in affected hives from around the country -- as well as in some hives where bees had survived. Those researchers have also found two other fungi and half a dozen viruses in the dead bees.
N. ceranae is "one of many pathogens" in the bees, said entomologist Diana Cox-Foster of Pennsylvania State University. "By itself, it is probably not the culprit ... but it may be one of the key players."
Cox-Foster was one of the organizers of a meeting in Washington, D.C., on Monday and Tuesday where about 60 bee researchers gathered to discuss Colony Collapse Disorder.
"We still haven't ruled out other factors, such as pesticides or inadequate food resources following a drought," she said. "There are lots of stresses that these bees are experiencing," and it may be a combination of factors that is responsible.
Historically, bee losses are not unusual. Weather, pesticide exposures and infestations by pests, such as the Varroa mite, have wiped out significant numbers of colonies in the past, particularly in the 1960s and 1970s.
But the current loss appears unprecedented. Beekeepers in 28 states, Canada and Britain have reported large losses. About a quarter of the estimated 2.4 million commercial colonies across the United States have been lost since fall, said Jerry Hayes of the Florida Department of Agriculture and Consumer Services in Gainesville.
"These are remarkable and dramatic losses," said Hayes, who is also president of the Apiary Inspectors of America.
Besides producing honey, commercial beehives are used to pollinate a third of the country's agricultural crops, including apples, peaches, pears, nectarines, cherries, strawberries and pumpkins. Ninety percent of California's almond crop is dependent on bees, and a loss of commercial hives could be devastating.
"For the most part, they just disappeared," said Florida beekeeper Dave Hackenberg, who was among the first to note the losses. "The boxes were full of honey. That was the mysterious thing. Usually other bees will rob those hives out. But nothing had happened."
Researchers now think the foraging bees are too weak to return to their hives.
DeRisi and UCSF's Don Ganem, who normally look for the causes of human diseases, were brought into the bee search by virologist Evan W. Skowronski of the U.S. Army's Edgewood Chemical Biological Center in Maryland.
Dr. Charles Wick of the center had used a new system of genetic analysis to identify pathogens in ground-up bee samples from California. He found several viruses, including members of a recently identified genus called iflaviruses.
It is not known whether these small, RNA-containing viruses, which infect the Varroa mite, are pathogenic to bees.
Skowronski forwarded the samples to DeRisi, who also found evidence of the viruses, along with genetic material from N. ceranae.
"There was a lot of stuff from Nosema, about 25% of the total," Skowronski said. "That meant there was more than there was bee RNA. That leads me to believe that the bee died from that particular pathogen."
If N. ceranae does play a role in Colony Collapse Disorder, there may be some hope for beekeepers.
A closely related parasite called Nosema apis, which also affects bees, can be controlled by the antibiotic fumagillin, and there is some evidence that it will work on N. ceranae as well.