‘Murder hornet’ has nothing on these mites
Meet the invasive parasite that changed beekeeping forever
WATERLOO REGION — While ‘murder hornets’ are dominating the headlines these days, they’re merely a distraction from the lurking, bigger invasive threat that has been quietly and systematically taking down honeybee populations across North America.
Meet the Varroa destructor mite. The name destructor says it all, for these mites have decimated bee populations everywhere. First documented in Asia in 1904, they were found in North America as early as the 1950s.
These mites are in the same family as ticks and spiders. They’re only about the size of a sesame seed but the fact that they can be seen without a microscope means they’re really big when compared to the size of their host, Apis mellifera, the common European honeybee. In human terms, a Varroa mite infestation would be like having a tick the size of a rat feeding on your back.
The Varroa mites are found everywhere in Canada except Thunder Bay and Newfoundland and Labrador. The Ontario Ministry of Agriculture’s website warns that if bees are kept anywhere outside these areas, they will be infested with Varroa mites.
The mites feed on the bees’ hemolymph (basically its blood) and fat tissue. The hemolymph transports a bee’s nutrients throughout its body, and the fat tissue contains its immune cells. In the process of removing bees’ natural immunity, Varroa mites also transmit deadly diseases. This includes deformed wing virus which results in shrivelled wings, bloated abdomen, learning problems and shortened life.
If left untreated, Varroa destructor mites destroy entire hives.
Paul Kozak, the provincial apiarist for Ontario, says the Varroa destructor mite is the main killer for honeybee colonies in all of North America. “This one mite is having devastating impacts throughout the world. They’ve changed beekeeping forever.”
An adult fertilized female mite enters a bee larvae cell just before it’s capped with wax. She then begins feeding on the larvae and lays eggs: first a male egg, then female eggs. Once the eggs hatch, the male mates with the females, and all the fertilized female mites emerge with the matured larvae. This bee is weakened and has a shorter lifespan. The mites move quickly from bee to bee. Once the queen stops laying larvae for the winter, the Varroa destructor mites then concentrate entirely on the adult bee population.
Ernesto Guzman, a professor of apiculture and the director of the honeybee research centre at the University of Guelph, says the mites were most likely introduced by importation of infested honeybee queens, either legally or illegally.
Although Varroa destructor mites have become resistant to many synthetically made miticides, Guzman said that without treatment, colonies have only a 50 per cent chance of survival through the winter when the infestation rate is higher than 6 per cent.
Guzman said there is some hope as research is demonstrating naturally occurring compounds, specifically essential oils including oregano, clove and thyme, are effective in controlling mite populations. Research is still ongoing for the best application method.
Another area of research is in selective breeding for natural resistance. Bees have two different kinds of behaviours that are natural defences against the mites. The first is hygienic practices, meaning the worker bees can smell infected larvae under its wax cap. They uncap the larvae and remove it, and this way disrupt the mite’s life cycle. The other habit is grooming. Some bees can scratch off the mites and kill them.
Not all bees are born with these behaviours. Guzman’s lab is researching how to breed bees that have these traits.