An illness killing tens of thousands of honeybee colonies across the United States has industry experts baffled and Canadian beekeepers concerned about the health of their hives.

Researchers in the United States are searching for the cause of the ailment, called colony collapse disorder.

Beekeepers from at least 22 states have reported unusual colony deaths. Some commercial beekeepers have reported losing more than 50 per cent of their colonies.

"We have seen a lot of things happen in 40 years, but this is the epitome of it all," Dave Hackenberg, of Lewisburg-based Hackenberg Apiaries, said by phone from Fort Meade, Fla., where he was working with his bees.

While the problem has been discussed in Canada, most apiaries north of the border have closed their hives for the winter.

Until the beekeepers check on the hives in late March, they won't know whether the colonies have suffered similar losses, said Doug McRory, provincial apiarist with the Ontario Beekeepers Association.

"It's been a poor fall but we haven't seen the same collapse here," McRory told CBC News Online. "But because it's winter we don't have a good handle on it. We'll have to wait until after winter to see how many are still alive."

A honey bee colony can have roughly 20,000 bees in the winter and up to 60,000 in the summer.

The bee population throughout North America has already faced a decline in recent years because of two parasitic bugs  — the varroa mite and the honey bee tracheal mite — that have caused viruses in the bee population.

Particularly hard hit by Colony Collapse Disorder are migratory operations where beekeepers take their colonies to warmer climates for the winter to help pollinate local agriculture.

McRory said moving colonies already puts stress on the bees, with beekeepers traditionally losing up to 20 per cent of their hives in the move.

Working towards a solution

Scientists at Penn State, the University of Montana and the U.S. Department of Agriculture are among the groups working to solve the mystery of the shrinking colonies.

Analysis of the dissected bees turned up weakened immune systems and an alarmingly high number of foreign fungi, bacteria and other organisms, according to Diana Cox-Foster, a Penn State entomology professor investigating the problem.

What separates this disorder from other known colony ailments is that no remains are found around the colonies. Instead, scientists assume the bees have flown away from the hive before dying. Another oddity is that no stronger bee colony swoops in and overruns the weakened hive.

"They seem to just abscond from the hive," said McRory. "That's what is really confusing."

With files from the Associated Press