Live or Let Die?

After two weeks in place in the bee hives, the thymol treatments have evaporated from their gelled state. The thymol vapors have killed a large proportion of the colony’s parasitic mites.   The mites fell from the bees and can be seen on the plastic inserts that covered the screened bottom boards and concentrated the thymol fumes. My 10-year-old grandson, Ethan, removes the inserts and hive spacer shims used to administer the thymol. Thymol is a product of the thyme plant, a common herb used to make pizza sauce. It is considered less dangerous to the honey bees than chemical miticides. The harsh miticides are known to lead to infertility in queens and drones. These agents have also led to resistant strains of parasitic mites.

In the future, it is hoped that we will not have to use any treatments at all to control mites. Great efforts are being made to breed strains of honey bees that are resistant to the deadly Varroa mites. These bees have a genetically heritable behavior trait that allows them to detect reproducing Varroa growing in the cells with developing honey bee pupae. The bees open the cells and remove the pupae along with the parasitic Varroa. This is called hygienic behavior. It is hoped that through genetic selection honey bees will evolve that can live in the presence of parasitic mites.  That seems to have occurred to a considerable degree with tracheal mites, but not yet with Varroa. In practicality, we are a long way away from pure honey bee genetic control of Varroa mites. Mite resistance is greatly diminished with each supersedure of a colony’s queen. A few beekeepers are attempting to use a “live or let die” approach to Varroa control, letting the mites select the resistant colonies. A more practical approach, however, seems to be an integrated pest management plan that employs numerous mite controls including “soft” chemicals, like thymol” as needed to rapidly knock down mite populations exceeding self-defined thresholds.

--Richard

Thymol Treatment for Varroa

Varroa mites were first detected in the United States around 1987. These visible parasitic mites followed by just three years the detection of microscopic mites that live in the trachea, or breathing tubes of the honey bee. The two species of mites decimated honey bee colonies. For a number of years it was common to not see a single honey bee in a stand of clover on a warm spring day when foraging bees should be abundant. Over the next couple of decades, tracheal mites became less of a killer of honey bees, but Varroa mites remained the most deadly pest of bees. Varroa mites puncture the exoskeleton of the honey bees and suck the bees’ blood, called hemolymph. The resulting wound exposes the bees to a number of viruses; several are suspected of being associated with Colony Collapse Disorder. In an attempt the stop the deaths of honey bee colonies, beekeepers relied upon chemical miticides to kill the parasitic mites. This was a most difficult task of attempting to kill a pest on a living insect without harming the insect. Each of the available miticides killed parasitic mites effectively for a while, and then strains of mites resistant to the chemicals replaced the original mites. Other strategies now being preferred include the use of “softer” agents, like organic acids and essential oils.

In the photo, I am inspecting a frame from the center of the brood nest. Here, bees are completing their last brood cycle of the year. In the center of the frame, a few capped cells hold pupae ready to emerge as adults. Around these capped cells are the empty cells of recently emerged bees. Farther out, a band of worker bees tend to uncapped honey. The outside edges of the frame contain honey capped with beeswax, the colony’s stored food for winter. Photographer and beekeeper, Brandon Dill, www.brandondillphotography.com, took this picture of me wearing protective gloves to apply thymol to treat a hive for mites.

--Richard