Scientists at the University of Guelph monitored colonies in six southern Ontario counties, counting the bees, weighing the colonies to gauge their food reserves and testing the bees for various mites and the Nosema fungus.

The aptly named varroa destructor was here, there and everywhere.

Varroa mites were associated with more than 85 per cent of colony deaths, according to the findings published online in the international journal Apidologie.

"There's been suspicion that the varroa mite was a major culprit for the losses we've been experiencing," said Ontario Beekeepers' Association president Tim Greer, noting that it's "excellent" that there's now scientific data to back it up.

"I believe that the Canadian beekeeping industry maybe under-estimated the effects the varroa mite would have on beekeeping here in Canada, when we knew that it was inevitable that it would sooner or later arrive to our Canadian bees."

The industry does treat for the varroa mite, but with varying degrees of success.

Greer said he believes that the presence of the mite contributes to weakening the condition of the honey bees and making them susceptible to other diseases, pests and viruses.

Ontario beekeepers have experienced three years of higher-than-average losses in the 30 to almost 40 per cent range, he lamented.

The not-so-sweet phenomenon of disappearing and dying bees, dubbed colony collapse disorder, has also affected these six-legged insect populations in other parts of Canada, the United States, Britain and other countries.

For the Ontario study, which spanned the period from fall 2007 to early summer 2008, biologist Ernesto Guzman and his colleagues looked at five different factors that could kill bees, and they were able to determine which one carried the most weight associated with colony mortality.

Varroa mites came out on top, followed by too-sparse beehive populations in the fall and insufficient food reserves for the winter.

"What's new is we were able to say this particular factor has more weight, this is second, this is third," Guzman said in an interview Wednesday from Guelph, Ont.

"This is why beekeepers should pay more attention in dealing with these three main factors."

Walter Sheppard, chair of the department of entomology at Washington State University, also said the "clear correlation" between varroa destructor and winter loss emphasizes the need to pay attention to mite levels.

"These mites have a very rapid reproductive life cycle and they quickly develop resistance to the different compounds that people are trying to use to control them," he said from Pullman, Wash.

"And if you kind of turn your head and don't pay attention for a little while, suddenly you have mite levels, when previously with the same treatment, the mites were controlled."

Guzman has been conducting research on environmentally friendly products made with the essential oils of thyme and oregano, which are effective at controlling mites but safe to bees.

"But applying them in the hives is a little bit difficult because most of them are released by evaporation, and therefore they are temperature dependent," he explained.

"If the temperature of application is low, it's cool, the evaporation rate might be low as well and the efficacy of the product is reduced."

It's too soon to say how bees are faring this winter because they're still cocooned in their hives and would become stressed if anyone unwrapped them to take a peek, Greer said.

They're clustered inside, forming a ball over their food stores. The core of the cluster remains at 21 C or above, and the bees on the outside migrate to the centre as they become chilled, he explained.

"The difficult time for bees is the months of March and April," he said, adding that the mysterious die-offs in the bee population have been at a great cost to beekeepers.

"If we experience those losses again this year, it could be the end for many beekeepers."

The majority of the province's 2,200 beekeepers are hobbyists, he said.

Ontario has about 80,000 hives, each one containing approximately 30,000 to 80,000 bees.