Prof Solves Bee Loss Mystery

March 03, 2010 - News Release

Varroa mites are the main culprit behind mysterious die-offs of honeybee colonies that have alarmed beekeepers, crop growers and the general public over the past three years, according to a new study by a University of Guelph biologist.

The study, published last month in the journal Apidologie, found that the parasitic mites were responsible for more than 85 per cent of honeybee colony mortality in Ontario. The next most important killers were too-sparse beehive populations in fall and insufficient food reserves for winter, says Prof. Ernesto Guzman, School of Environmental Sciences.

About one-third of Ontario's colonies died in the winter of 2006/07, and another one-third died in 2007/08 — about three times the expected winter loss in average years. Some beekeepers in parts of the province lost all their hives.

Guzman says his study offers solutions for beekeepers and crop growers, many reliant on honeybees for honey production and for pollination of many other food crops.

"Varroa mite is the main culprit in colony mortality in Ontario," he says. "Eighty-five per cent of mortality cases were associated with varroa mite."

He studied 408 commercial colonies in six southern Ontario counties, including Wellington, Middlesex and Norfolk. In fall 2007, spring 2008 and early summer 2008, he counted bees in colonies and weighed colonies to gauge food reserves. He also tested bees for varroa mites, tracheal mites and the Nosema fungus, all known to cause infection in bees.

Besides varroa mite infestation, weak populations and low food reserves in the fall can cause colony mortality, says Guzman. "We're pretty sure we've solved a great deal of the mystery."

Based on his study, he recommends beekeepers strictly follow a mite treatment regimen, feed their bees enough sugar syrup and avoid splitting colonies too late in the season.

Tim Greer, president of the Ontario Beekeepers' Association, says the Guelph study will help the province's roughly 2,200 beekeepers improve their management practices. He adds that the industry still needs reliable treatments for varroa mites. "We've identified the problem — now it's coming up with treatment."

Greer says experts are also concerned about effects of systemic pesticides on bees in other parts of the world, although those products appear not to be a major problem in Ontario.

In his Guelph lab, Guzman is studying genetic techniques to learn more about honeybee infections and to help breeders develop better bees.

This research was funded by the Ontario Beekeepers' Association; the Ontario Ministry of Agriculture, Food and Rural Affairs; the Natural Sciences and Engineering Research Council; and the Inter-American Institute for Co-operation on Agriculture.

Prof. Ernesto Guzman
School of Environmental Sciences
519-824-4120, Ext. 53609

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University of Guelph
50 Stone Road East
Guelph, Ontario, N1G 2W1