The Varroa mite is a Pandora’s box that humans will never be able to close. They are here to stay and they aren’t going anywhere despite all our efforts to treat them away. According to USDA’s Report on Honey Bee Health (PDF), published in 2012, the parasitic mite, Varroa destructor, remains the single most detrimental pest of honey bees.
It is my belief that, by treating bees for Varroa using chemicals like oxalic acid and formic acid or by applying various beekeeping techniques in an effort to help the bees to survive mites, we are unintentionally making weaker bees and breeding stronger mites. In an ideal world, mites and bees would live together in balance where the mites get what they need without completely killing off their host. In fact, it is in the mites’ best interest for the honey bees to find ways to naturally keep these pests at bay.
At the USDA Varroa Mite Summit, which took place in 2014 at the USDA Animal and Plant Health Inspection Service in Maryland, topics such as Varroa biology and its effects on colony survival as well as breeding resistant bees were discussed. Presentations with respect to the breeding of resistant bees focused on selection of resistant bees from colonies that exhibit robust survival rates following exposure to high Varroa infestation. Bees that have the ability to remove mites from their bodies via grooming have lower mite levels. Thus, selection for grooming traits in adult bees could produce bees with greater resistance to Varroa mites.
External forces cause certain traits to be selected and passed on to offspring to enhance their chance of survival and reproduction. In an article titled “Honey bees rapidly evolve to overcome new disease“, the Okinawa Institute of Science and Technology and Cornell University studied the genetics of a wild honey bee colony by comparing the DNA of specimens collected in 1977 with bees collected from the same forest in 2010. They found that the strongest driver of the observed changes was natural selection.
According to Robert Danka of the USDA-ARS Honey Bee Breeding, Genetics and Physiology Laboratory, in Baton Rouge, there are Varroa-resistant (VR) honey bees that exist whose colonies host mite populations that remain small enough to allow beekeepers to eliminate or reduce miticide treatments.
While the Keeping Backyard Bees website is not particularly targeted towards the commercial beekeeping industry, it does seem that most of the pushback regarding treatment-free beekeeping comes from those beekeepers whose primary source of income is derived solely from the profession of keeping bees. Thus, it is fitting for me to mention in this article that honey bees surviving Varroa mite infestation without treatment by commercial beekeepers has been documented in such places as Russia, France and in North America. There are well-known breeds of honey bees in existence now referred to as Russian honey bees and Minnesota Hygienic honey bees that exhibit certain behaviors to control mite levels and the negative impacts of mites in a hive. VR bees are being used successfully with some beekeeping operations having not used miticides for more than 10 years. However, Robert Danka goes on to say, “It seems likely… that extensive use of VR bees in commercial beekeeping likely will not occur until miticide treatments become unreliable.”
Studies performed by the Swedish University of Agricultural Sciences & University of Maryland also show how honey bee colonies can survive Varroa destructor infestation without treatments. A population of European honey bees (Apis mellifera) surviving Varroa destructor mite infestation on an island in Sweden demonstrates that a balanced host-parasite relationship may evolve over time if colonies are left without mite control. This particular population has survived since 1999 with exposure to severe mite infestation selection pressure. Surviving honey bee colonies limited the mite population growth by suppressing mite reproductive success.
Research by Joachim R de Miranda in the Department of Ecology of the Swedish University of Agricultural Sciences shows that the principal Varroa-transmitted viruses are the acute bee paralysis virus (ABPV) and deformed wing virus (DWV) virus-complexes. Bees naturally resistant to mites are better at surviving the infection, possibly due to fewer secondary viruses and superior general health.
Another example of a pest-host relationship that shows how species have the ability to deal with new parasites and selective pressures naturally is the silent cricket found in the Hawaiian Island of Kauai. Over time, the population of male crickets eventually stopped chirping in order to evade the parasitoid flies and escape from being eaten by maggots.
To put it plainly, honeybees are either going to find a way to live with Varroa or it will come to a point where honeybees will become so dependent upon humans and their interventions that the bees will become fat and lazy like they do in Solomon Parker’s proverbial story of the Gazelle in the trailer.
Selective pressures have been applied naturally to honeybees for thousands of years. I’m confident that natural selection will eventually do its job if left alone. We’ll come out with strong bees and weak mites, which is what beekeepers around the world actually want.