Long the scourge of beehives, the varroa mite has emerged as the leading suspect in the mysterious decline of honeybee colonies across Canada, says a University of Guelph researcher.
In an article in the online scientific publication Apidologie, which is devoted to bees, Ernesto Guzman and his research team say that 85 per cent of the colony deaths in Ontario are the result of the mite.
The researchers tracked 408 bee colonies across southern Ontario from the fall of 2007 to the early summer of 2008. More than a quarter didn’t survive the winter and the finger of blame falls mainly on the mite.
Twenty-seven per cent of the colonies examined in the fall were dead by the spring. Of the colonies that died, Guzman and his team found that 85 per cent of colony deaths could be attributed to the mite.
“There’s been suspicion that the varroa mite was a major culprit for the losses we’ve been experiencing,” Ontario Beekeepers’ Association president Tim Greer told reporters.
“I believe that the Canadian beekeeping industry maybe underestimated 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,” he says. The industry does treat for the mite, but with varying degrees of success.
Greer said he believes that the presence of the mite contributes to weakening the condition of the honeybees and making them susceptible to other diseases, pests and viruses.
Ontario beekeepers have lost up to 40 per cent of their hives in recent years, he added.
In addition to the mites, Guzman believes that too-sparse beehive populations in the fall and insufficient food reserves for the winter contribute to the loss of colonies.
“What’s new is we were able to say this particular factor has more weight, this is second, this is third,” Guzman told reporters. “This is why beekeepers should pay more attention in dealing with these three main factors.”
In combination with a small colony size and low fall food reserves, the varroa mite creates “a perfect storm for the colony to die,” he adds.
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 says. “If the temperature of application is low, 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.
They’re clustered inside, forming a ball over their food stores. The core of the cluster remains at 21C or above, and the bees on the outside migrate to the centre as they become chilled.
“The difficult time for bees is the months of March and April,” Greer said. It’s important for the financial well-being of beekeepers to find out what causes the colony losses.
“If we experience those losses again this year, it could be the end for many beekeepers,” he adds.
Roughly three-quarters of flowering plants rely on bees, birds and other pollinators to allow them to reproduce.
Beekeepers have wrestled with the mite for the last two decades and it seems to have developed a resistance to the chemicals used to control them.