Managing amitraz resistant Varroa mites in honey bee colonies: Effects of winter treatment with slow-release oxalic acid

The parasitic Varroa destructor mite is a leading cause of honey bee colony losses in the northern hemisphere. Amitraz is the most commonly used acaricide by commercial beekeepers to control Varroa mites; however, continued reliance on it has led to the emergence of amitraz resistant mite populations throughout the country. We wanted to determine whether treatment with a non-amitraz acaricide (i.e., rotation) during winter would reduce the proportion of mites that were resistant to amitraz while effectively controlling mite infestations of colonies. In coordination with a commercial beekeeper with amitraz resistant mites, we tested two slow-release oxalic acid treatments as alternatives to amitraz. We compared a commercial formulation (Aluen CAP^®) and a custom-made formulation (oxalic acid and glycerin in SpillTech^® absorbent pads) against an amitraz-based treatment (Apivar^®) included as a positive control. Mite infestation of adult bees, proportion of mites resistant to amitraz, and adult bee population of colonies were all measured. Preliminary results show minimal differences in mite control among treatment groups; however, Aluen CAP^® appeared to have a negative effect on colony population and overall colony survival. Furthermore, neither alternative slow-release oxalic acid product reduced amitraz resistant mites from the population.