Study Points to Virus in Collapse of Honeybee Colonies
Friday, September 7, 2007
Scientists yesterday identified a virus as one of the likely causes of the recent wave of honeybee colony collapses across the country.
The study, co-authored by researchers at Pennsylvania State University, Columbia University, the U.S. Department of Agriculture and several other institutions, suggests that the Israeli acute paralysis virus (IAPV) helps trigger the mysterious condition known as colony collapse disorder, which destroyed about 23 percent of U.S. beehives last winter. The paper is being published today in the journal Science.
Beekeepers, scientists and public officials have been searching for the cause of the disorder, which surfaced in 2004 and was formally recognized last year. Unlike other diseases that strike hives, the collapse disorder leaves a colony without most of its worker bees despite the presence of plentiful food, a queen and other adult bees. It has devastated an industry that produces honey and pollinates lucrative crops such as almonds, oranges and apples.
The scientists who authored the paper emphasized that they have begun to solve the puzzle but have yet to determine exactly what causes a colony's abrupt decline.
"This is a major finding," said Columbia University professor W. Ian Lipkin, an epidemiologist who normally focuses on human diseases. "What we have at present is a marker. We do not think IAPV alone is causing this disease."
Israeli scientists had already identified a lethal strain of the virus in their country. Lipkin said in a telephone interview that U.S. researchers had found a closely related virus that "may be somewhat muted," or less virulent. Other factors, such as the varroa mite, a well-known parasite that attacks bees, may be weakening bees' immune systems and making them more vulnerable to the virus.
Using the recently mapped honeybee genome, American scientists were able to identify genetic material from viruses and other pathogens in bees collected over the past three years from healthy and sick colonies across the country. They found evidence of the virus in 25 of 30 affected colonies, but just one of 21 unaffected hives.
"The only candidate which was left standing at the end of this very rigorous process was IAPV," Lipkin said.
Penn State entomologist Diana L. Cox-Foster, the paper's lead author, said she and her colleagues found no evidence that cellphone signals were affecting the bees, as some have speculated. Crops treated with pesticides, which many beekeepers suspect are harming the bees, "could be helping to stress the bees, or acting as a potential trigger," she said.
Jim Doan, a third-generation beekeeper in western New York who takes the bees to central Florida each winter to pollinate citrus crops, said the scientists were underestimating pesticides' impact. Doan, who lost 90 percent of his hives last winter and has lost at least 15 percent so far this year, said he believes chemicals on cucumbers, tomatoes, squash and other crops may be responsible.
"Anything that we're doing doesn't seem to be working," Doan said, noting that he and other beekeepers have changed the way they manage their hives. "Financially, this is breaking me. I may be out of business by the end of the year."
The researchers said Australian honeybees brought into the United States in recent years may be the source of the virus. Australia does not have the varroa mite, which may explain why it has not experienced the disorder. Other countries, including Israel, have had cases of colony collapse, though not on the same scale as the United States.
It is unclear whether U.S. authorities will bar future imports of Australian honeybees in light of the new research. Jeffery Pettis, a researcher at the Agriculture Department's Bee Research Laboratory in Beltsville, said his office is meeting with the department's Animal and Plant Health Inspection Service to discuss "what needs to be done."
In the meantime, researchers have replicated the virus and handed it over to USDA officials, who will inject it into healthy bees to see whether it causes their colonies to collapse.
"Even in bad times, good things happen. We have new leads," Pettis said, adding that the number of U.S. bee colonies has dropped from 5 million in the 1940s to 2.5 million today. "We don't have a great deal of buffer. We just need to maintain healthy pollinators."
Staff researcher Bob Lyford contributed to this report.