Mite Affects Plight of the Honeybee

Beekeeping techniques affect honeybee health

Ernesto Guzman

Not many people realize just how much we depend on bees. Some two-thirds of the world’s crops require pollinators and about one-third of everything we eat in North America is thanks to bees.

For example, one million honeybee hives, each containing up to 60,000 bees, are needed to sustain the almond crops in California alone.

For commercial pollination, the western honeybee (Apis mellifera) is the bee of choice, says entomologist Ernesto Guzman, a professor in the School of Environmental Sciences and head of the Honey Bee Research Centre. The centre maintains 200 to 300 honeybee colonies, primarily for research and teaching.

“Sales of honey are relatively small considering that as many as 60,000 honeybees can live together as a colony in a single hive,” he says. “Beekeepers typically maintain 30 to 50 hives in a single location and rent hives out. The hives can be moved to different locations – 15,000 colonies from Ontario are trucked to New Brunswick, in fact – to blueberry growers, among others.

“Beekeepers across North America employ these practices. Rental hives are a vital source of income for the beekeeping industry and crucial for raising the crops that we eat. That’s why it’s of such concern that, since 2007, the honey bee mortality rate was more than 30 per cent a year, four years in a row. That represents an unprecedented rate: three times the expected average loss. In Ontario alone, there has been a decline in the bee population of more than 40 per cent.”

North America and many European nations, such as Britain, France, Germany, Italy and Spain, share a similar experience. Such high mortality rates are not found, however, in the southern hemisphere, such as in Africa, South America and Southeast Asia. Guzman suspects that this is due to different beekeeping methods, climates and types of bees.

While researchers agree that a combination of factors curtail the lifespan of honeybees in North America, they have yet to conclude which factors contribute the most.

“Many elements of modern beekeeping are hard on bees,” Guzman says. “For instance, the way in which they are transported is a source of stress. The hives are closed up for hours at a time. In enclosed trailer trucks, bees endure shaking and are subjected to variations in temperature that are unnatural for them. Then they are released, sometimes thousands of kilometres away, into a foreign environment. Bees are able to fly up to three kilometres to gather pollen, but the agricultural environment typically offers them only acre upon acre of one type of plant, as far as they can fly. So they are forced to live on an unbalanced diet of just one type of pollen over an extended period of time, while normally an apiary would have access to diverse plants and types of pollen.”

Another factor in the demise of bees is that beekeepers split their colonies up into separate rental hives, creating smaller colonies. Studies have shown that smaller populations of bees are weaker – those with fewer than six combs entirely covered with bees have a significantly lower survival rate. Some studies also have linked the use of certain pesticides, most notably neonicotinoids, to the startling decline in North American bee populations.

According to Guzman, blood-sucking mites that live on bees are also to blame. The mites transmit potentially life-threatening viruses to their hosts; one parasitic mite can decrease a bee’s life expectancy by 50 per cent.

“Mites are relatively new pests of the honeybee,” he says. “Our bee management, unfortunately, helps spread mite infestations. One type of mite called Varroa destructor attacks both Apis mellifera and Apis cerana (the eastern or Asiatic) honeybees. These mites are very new to bees in the western world. The original Varroa host was Apis cerana in Southeast Asia, where the bees and mites have co-existed for a long, long time. The Varroa infestation of the western honeybee has been known to science for less than 60 years.”

The presence of this mite in Canada was first discovered in the 1990s. Initially, the mites were controlled with synthetic pesticides called acaricides.

“They appeared to work well at first, killing 99 per cent of the mites, but since about 2001, the mites have been developing resistance to those chemicals,” says Guzman. “Now that the pesticides are less effective, there has been resurgence in mites, to the point where parasitic mites have become a major factor in the mortality of honey bee colonies.” A study co-authored by Guzman and published in 2010 showed that Varroa destructor mites were associated with 85 per cent of bee deaths during a single winter in Ontario.

Another honeybee parasite that originated in Southeast Asia is the microscopic spore-forming Nosema ceranae, known since 2006 to invade and destroy cells in the intestinal tract of the western honeybee. This species was recently found in Canada, but a similar species known as Nosema apis has been known for a long time to affect Canadian bees. Both species were recently reclassified as a fungus. Bees become infected when cleaning comb cells soiled with feces from infected bees and through contaminated water. It causes the most widespread of adult honey bee diseases: nosemosis.

“The first cases of Nosema ceranae discovered in Apis mellifera were not statistically associated with bee mortality in Ontario, and although Spanish research showed there was a relationship, other studies had not confirmed those findings,” says Guzman.

His laboratory works with managed western honeybees exclusively. He studies the impact of Varroa and Nosema parasites on the honeybee immune system. Guzman is also studying genetic techniques to learn more about honeybee infections and to help breeders develop better bees.

As part of a tradition that began when the first beekeeping courses were taught at the Ontario Agricultural College in 1894, Guzman hopes that U of G’s renowned apiculture research and education will help the province’s beekeepers improve their management practices. “Research can only do so much,” he says. “Lots of stresses are bound to remain for bees; this is the price of modernity.”

The University recently established the Rebanks Family Chair in Pollinator Conservation in the School of Environmental Sciences to launch new research initiatives, enhance teaching capacity and work with existing networks in the field.