A honeybee buzzes near cherry blossoms. (Robin Loznak/Daily Inter lake/Associated Press)

There's a new clue to explain why so many honeybees are dying in North America, primarily in the United States but also in Canada. Billions of worker bees have died in recent years in a phenomenon known as colony collapse disorder, referred to as CCD by scientists, beekeepers and farmers.

The online edition of the journal Science reports in its Sept. 8 issue that a virus called the Israeli acute paralysis virus may be a contributing cause for CCD.

"Our extensive study suggests that the Israeli acute paralysis virus (IAPV) may be a potential cause of colony collapse disorder," says W. Ian Lipkin, of the Center for Infection and Immunology at the Mailman School of Public Health, Columbia University. "Our next step is to ascertain whether this virus, alone or in concert with other factors such as microbes, toxins and stressors, can induce CCD in healthy bees."

According to some Canadian entomologists, the virus is likely opportunistic, affecting honeybees already stressed and weakened by other factors.

Environmental disaster

The death of so many commercial honey bees (apis mellifera) as a result of CCD is considered a looming environmental disaster, because the bees are a vital link in our food chain, responsible for pollinating about a third of all the food crops in human diets.

The U.S. Department of Agriculture says that 24 U.S. states have reported the disorder, which puts at risk about $24.6 billion worth of crops that depend on bee pollination. The study reported in the journal Science says that in destroyed colonies the IAPV virus is nearly always found, while healthy hives are free of it.

Researchers Lipkin and Diana Cox-Foster, entomology professor at Pennsylvania State University, used a rapid genome sequencing technique called "pyrosequencing" to catalogue the entire variety of micro-organisms that honey bees harbour. After comparing their sequences with known sequences in public databases, they identified symbiotic and pathogenic bacteria, fungi and viruses in healthy and CCD-afflicted bee colonies.

Chinese royal jelly

Lipkin and Cox-Foster then tested samples collected over three years across the U.S. from normal and CCD-afflicted hives. They also tested royal jelly from China, which is fed to bee larvae to start a new colony, as well as healthy bees from Australia, in an attempt to find a source for an infectious agent.

"After detailed statistical comparison of all the samples, the molecular signs of acute Israeli paralysis virus appeared to be associated with CCD," says a release from the American Association for the Advancement of Science.

"This research gives us a very good lead to follow, but we do not believe IAPV is acting alone," said Jeffrey S. Pettis, research leader of the Bee Research Laboratory at the U.S. Department of Agriculture. "Other stressors to the colony are likely involved. Those stressors could be poor nutrition, pesticide exposure and parasitic mites."

Dr. Peter Kevan, an associate professor of environmental biology at the University of Guelph in Ontario, told CBCNews.ca in April 2007 that CCD in the United States is "an absolute catastrophe."

There wasn't much talk of CCD in Canada at the time, but worrisome honeybee losses had been noted, some 18 per cent a year over the past 10 to 15 years, according to Doug McRory, provincial apiarist with the Ontario Beekeepers Association.

Asked about the Israeli acute paralysis virus, McRory told CBCNews.ca: "I've never heard of the virus and most of the people in the apicultural [study of bees] community have never heard of it, which makes it interesting."

Kevan of the University of Guelph in Ontario said in April 2007 that CCD might be caused by parasitic mites, or long cold winters, or long wet springs, or pesticides, or genetically modified crops — or stress.

Stressed-out honeybees

"We've been pushing them too hard," Kevan told CBCNews.ca. "And we're starving them out by feeding them artificially and moving them great distances." Kevan was referring to the practices of migratory beekeepers, who transport hundreds of thousands of beehives across the continent on flatbed trucks to pollinate crops in different states, which causes enormous stress on the bees.

He conducted a study on bee ailments that lists stress factors such as confinement, temperature fluctuations and mechanical vibrations during transport, which are upsetting to the bees, akin to jet lag on airplane travellers.

Honeybee enemies include two varieties of parasitic mites, one called the tracheal mite, another the varroa mite, which started infesting bee colonies in the mid-1980s. The tracheal mite, believed to have entered the U.S. from Mexico, sucks blood from honeybees by burrowing into a bee's windpipe. The larger varroa mite lives on the outside of bees and destroys the insects' reproductive cycle.

Honeybees are important for much more than honey, though the honey alone is worth hundreds of millions of dollars. The real impact of honeybees is on other crops — apples, cucumbers, alfalfa, blueberries, almonds, squash, watermelons, cantaloupes and a huge variety of other fruits and vegetables — that constitute an industry worth tens of billions of dollars. In parts of South America, bees actually pollinate timber trees.

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