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Parasites Threaten Crop Pollination

February 23, 2000
University Of Guelph
As honey bee colonies slumber through the harsh winter season, two potentially devastating parasitic mites are threatening their survival.

As honey bee colonies slumber through the harsh winter season, two potentially devastating parasitic mites are threatening their survival.

The problem is actually two parasites -- the tracheal and varroa mites -- that have migrated from the U.S. and are making a new home in Ontario, Canada beehives. These mites have the potential to devastate the province's bee population, causing not only a shortage of honey but major problems for fruit and vegetable producers who rely on bees to pollinate their crops. It's estimated that honeybees account for 80 per cent of all pollination, and are responsible for ensuring approximately one-third of the food supply.

But a research program at the University of Guelph is stemming the potential devastation with an integrated program that uses genetics and traditional pest control methods. Led by Medhat Nasr, a technology transfer specialist for the Ontario Beekeepers Association based at the U of G, the program has achieved an 80 per cent drop in mortality rates in bees infected with mites, and increased the production of queen bees -- which are crucial for commercial beekeeping -- from 2,500 in 1990 to approximately 15,000 this year.

"Bees are mainly used for crop pollination in Ontario, not for honey production,"says Nasr. "If these parasitic mites take over, we'll see a drastic decline in crop yields over the next few years."

Varroa mites infest bees at an immature stage in their development, leading them to grow into adults with deformed wings, low weight and a greatly reduced lifespan. Equally devastating is the tracheal mite which lives inside the bee's trachea (breathing tube). Once inside, tracheal mites breed and reproduce, filling the bee's lungs with their offspring and inhibiting breathing capacity. If an infected bee doesn't suffocate, its ability to fly long distances to pollinate crops is hindered.

Nasr is employing integrated pest management (IPM) techniques to control the mites. Rather than solely relying on chemicals for pest control, IPM integrates other methods such as breeding and special management practices to keep pest populations at bay.

Recently, Nasr successfully bred bees that are attractive to the tracheal mites for a shorter span of their life, decreasing the opportunity for mites to infect young bees.

Nasr has also studied the effectiveness of formic acid as a means of repelling mites. Formic acid is a natural product produced by ants, and is also found in honey. Nasr found formic acid to be 90- to 95 per cent effective against both tracheal and varroa mites, and it leaves no residue in the honey or wax.

Part of Nasr's mite control program involves alternating the use of Apistan— a chemical currently used to control mite infestations— with formic acid. Generally, Apistan is applied to hives twice a year, but by alternating it with formic acid, beekeepers need to apply it only once. This reduces chemical use and delays the emergence of Apistan-resistant mites which, according to Nasr, have already emerged in the U.S.

"IPM doesn't lead to the complete eradication of the mites," he says. "But it does reduce the likelihood of beekeepers becoming over-reliant on a pesticide. It's more effective in the long run."

This research is sponsored by Agriculture and Agri-Food Canada through the CanAdapt program (administered by the Agricultural Adaptation Council), the Ontario Ministry of Agriculture Food and Rural Affairs and the Beekeepers of Ontario.

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University Of Guelph. "Parasites Threaten Crop Pollination." ScienceDaily. ScienceDaily, 23 February 2000. <>.
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