A wet fall, a long winter and an influx of invasive species are the usual suspects investigators have rounded up in search for clues to a malady crippling honeybee populations in southern Ontario and other parts of Canada.

But so far Canadian apiarists aren't sure whether the hive losses in this country are connected with those in the United States and Europe, where a mystery illness is causing honeybee colonies to leave their hives and never return.

Beekeepers from 24 U.S. states have reported losses of up to 90 per cent of their hives from the mystery ailment — called Colony Collapse Disorder, or CCD — that investigators say is unlike anything they had encountered before.

Leaving the hive to die is not uncommon for honeybees, said Doug McRory, the provincial apiarist for the Ontario Beekeeping Association. But with CCD, pollen and honey are abundant in the hives and yet other bees are staying far away, suggesting something else is at work.

It's a different situation in the Niagara region of southern Ontario, where there has been little pollen found in the abandoned hives, McRory said.

Weather has likely played a key role in the winter losses in southern Ontario, where Ontario's commercial apiarists have lost about 23,000 of their 76,000 hives this winter, McRory said.

McRory suggested a wet fall may have led to a decrease in pollen and nectar production, which in turn led hives to produce a smaller brood. The smaller hives likely put greater stress on older, adult bees more susceptible to disease, and an unusually long winter added to the stress when the bees clustered over the winter, he said.

Localized effect

Lending credence to the theory is the localized effect of the honeybee depopulation: While southern Ontario was hard hit, apiaries in Northern Ontario have seen far fewer losses.

McRory said apiarists across the province are calling him up to ask whether they have CCD, a sign the harsh winter has taken its toll. But the symptoms, he says, don't match what's happening in the U.S.

McCrory thinks the likely culprit in the United States is the small hive beetle, a tiny insect that came to the U.S. from South Africa in 1998 and which has been known to cause damage and fermentation in the honey that leads the bees to flee the hive. The small hive beetle has yet to make its way into Canada, he said.

Competing theories

It's one theory, but not the only one out there.

May Berenbaum, head of the entomology department at the University of Illinois, said pesticide use may be linked to the problem. Berenbaum told CBC News there are some chemicals that may be causing bees to forget their way home.

"There are some neurotoxic insecticides that can interfere with honeybee memory, and that might be manifested in disruption of their orientation and navigation abilities," Berenbaum said.

A German study conducted by Professor Jochen Kuhn of Landau University and reported in Britain's Telegraph newspaper this week offered another, less conventional, culprit: radiation from cellphones and cellphone towers.

To conduct the study, Kuhn placed cellphone handsets near hives and found the bees avoided their homes when the phones were radiating frequencies in a range from 900 to 1800 megahertz, the standard range for most cell phones.

Whatever the cause, the disappearing honeybee populations pose a threat beyond honey production.

Crucial role

Honeybees play a role in pollinating a number of Canadian fruits, vegetables and crops, particularly cucumbers, melons, blueberries and cranberries and canola, according to the Canadian Honey Council.

A 1998 study by Agriculture and Agri-Food Canada estimated the value of the bees to pollination at $732 million, a value the council now says has climbed to more than $1 billion.

There are about 10,000 beekeepers in Canada, operating a total of 600,000 honeybee colonies, according to the CHC.

Alberta, Saskatchewan and Manitoba produce about 80 per cent of Canada's 154 million kilograms of honey annually.

With files from the Canadian Press