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The sudden and mysterious disappearance of honeybees in the United States over the past year may be due to a virus, according to a new research paper by an international team of scientists.

The pathogen, called Israeli acute paralysis virus, has been detected in almost all bee hives tested in survey of those afflicted by what has become known as colony collapse disorder, but it is rarely found in healthy hives.

The discovery will likely help put to rest rampant speculation about the source of the strange collapse in U.S. bee populations.

U.S. bee keepers began noticing slight declines in bee numbers in 2004, although the scale of deaths increased dramatically in the past year, with some apiaries losing up to 90 per cent of their hives. These were baffling die offs in which the workers in colonies of the highly social insects would disappear without a trace.

The enormous scale of the destruction prompted worry that useful insects might be being killed by some new environmental threat. There has been speculation that the missing bees might have become disoriented by the recent proliferation of radiation from cell phone towers and died while foraging for nectar. Other fears centred on new genetically modified crops' poisoning the bees.

Scientists who worked on the new research, which is being published in the current issue of Science Express, now discount those theories and believe that the most likely explanation is that the bees are being harmed by a new infectious agent.

”Our extensive study suggests that the Israeli acute paralysis may be a potential cause of colony collapse disorder,” said Dr. Ian Lipkin, director of Columbia University's infectious diseases laboratory.

The death of bees has caused widespread alarm in the agricultural industry. Although most people associate bees with honey, the insects are far more important for their role in pollinating crops. About 90 foods, everything from apples to cucumbers, depend on bees to ensure that fruits and vegetables develop.

Any threat to bee numbers could therefore affect the global food supply. An estimated $2-billion worth of crops in Canada depend on honeybees for pollination, and about $15-billion (U.S.) in the United States, where the collapse has already led to difficulties in pollinating crops.

The researchers also found the virus on bees imported into the United States from Australia and in royal jelly samples from China. Royal jelly is the food bees produce for queens, but it is also sold as a health food for humans.

The discovery of the virus has raised speculation that the United States inadvertently allowed it into the country through the import of Australian bees, a practice allowed in 2004 under pressure by the agricultural industry to boost the number of hives available for pollinating high value crops, such as almonds.

The import of the bees coincided with the first reports of unusual problems in bee colonies.

All the hives infected with the virus either used Australian bees or had been stored near colonies that imported the insects from Australia.

To date, there have been no known cases of colony collapse disorder in Canada, according to Danny Walker, president of the Ontario Beekeepers' Association.

He said that Canada does not follow the U.S. practice of importing entire bee colonies from Australia, although it does allow apiaries to purchase individual queens, which are then seeded into domestic hives.

Scientists who discovered the virus – by analyzing genes of microorganisms found in bees – say they do not know if the pathogen itself causes colonies to die off, or if it weakens the bees and makes them more susceptible to death from pesticides, poor nutrition and parasitic mites.

The virus was first described in Israel in 2004. Researchers there noted that infected bees – which exhibited shivering wings and paralysis – would die just outside their hives.

One perplexing finding is that bees in Australia do not seem to be affected by colony collapse disorder. The researchers speculated that the reason might be that bees there are not infected with varroa mites, which are found throughout North America. The mites are able to suppress the immune system of bees, making them more vulnerable to other threats.