5.3. Chemical control
The overriding constraints for chemical control of mites are that the chemicals must be effective against the target (i.e. mites) and harmless to bees, and they must not accumulate in hive products. Because bees and mites are both arthropods, many of their basic physiological processes are similar, narrowing the possibilities for finding suitable toxicants. To control HBTM, the material must be volatile to reach the bee, inhaled, and lethal only to the parasite.
Based on early research by Giordani (1977), menthol was widely tested and registered for treatment of hives in the United States and Canada. Menthol is extracted from the mint plant Mentha arvensis and is sold as crystals, which can be applied inside hives (usually 50 g of crystals in a nylon mesh sac are placed on the top bars of frames). In cold conditions, menthol is ineffective for mite control because the rate of vaporization is too low to provide concentrations lethal to the mites. Some Canadian beekeepers obtained good results under cool conditions by applying pieces of cardboard saturated with a mixture of menthol (dissolved in alcohol) and vegetable shortening to hives. If the air temperatures outside are too high, menthol vapours may drive bees out of their hives. If bees are hanging outside the colony entrance in treated colonies, crystals should be removed until temperatures drop.
The synthetic pesticide amitraz, (sold as Apivar®) has been used for HBTM control. Check current regulations to determine its registration status. Formic acid has also been used against A. woodi (Hoppe et al., 1989; Amrine and Noel, 2006; Underwood and Currie, 2009; Hood and McCreadie 2001). Widely used as a treatment for varroa mites, formic acid (along with other acaricides used against varroa) may be contributing to current lower populations of HBTM in North America. As many of these chemicals could have a negative impact on both the bees and the honey, they are not recommended as both non-toxic vegetable shortening and resistance queen stock are better alternatives.