Using oxalic acid in water solution in control of Varroa mites and its influence on honey bees

We studied the toxicity of water solutions containing various concentrations of oxalic acid dihydrate to bees and Varroa mites (Varroa destructor) using by spraying honey bee (Apis mellifera) colonies with no brood or little brood in beehive conditions in West-Viru County, Estonia. A water solution of 0.5% OA gave effective control of the mite and was not toxic to bees whereas higher concentrations of OA (1.0 and 1.5%) were highly toxic to bees. In autumn, spraying test colonies that had little capped brood once or twice with a 0.5% OA solution gave effective mite control (92.94 ± 0.01% and 91.84 ± 0.02%, respectively) with no noticeable toxicity to bees.