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, was detected in almost all bee hives tested during a survey of hives afflicted by what has become known as colony collapse disorder. The pathogen 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.

Beekeepers in the United States began noticing slight declines in bee numbers in 2004. The scale of deaths increased dramatically in the past year, with some apiaries losing up to 90 per cent of their hives. The workers in colonies of the highly social insects would disappear without a trace.

The enormous scale of the destruction prompted worry that some new environmental threat might be killing useful insects. Some speculated that the missing bees might have become disoriented by the recent proliferation of radiation from cellphone towers and died while foraging for nectar. Others theorized that new genetically modified crops were poisoning the bees.

But scientists who worked on the new research, which is being published in the current issue of Science Express, now believe the most likely explanation is a new infectious agent.

“Our extensive study suggests that the Israeli acute paralysis may be a potential cause of colony collapse disorder,” said Ian Lipkin, an epidemiologist at Columbia University.

The death of bees had 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, ranging from apples to cucumbers, depend on bees to ensure that fruits and vegetables develop.

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

The researchers also found the virus on live 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. This was allowed in 2004, at the urging of 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 were stored near colonies that imported the insects.

To date, Canada has had no known cases of colony collapse disorder, said Danny Walker, president of the Ontario Beekeepers’ Association.

He said Canada doesn’t allow the importation of entire bee colonies from Australia, although it does allow apiaries to buy individual queens, which are then seeded into domestic hives.

Scientists who discovered the virus, and analyzed genes of micro-organisms found in bees, said they do not know if the pathogen itself causes colonies to die off, or whether it weakens the bees and makes them more susceptible to pesticides, poor nutrition and parasitic mites.

The virus was first described in Israel in 2004, leading to its name. 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 don’t seem to be affected by colony collapse disorder. The researchers speculated the reason might be that bees there are not infected with varroa mites, which are found throughout in North America. The mites suppress the immune system of bees, making them more vulnerable to other threats.