For a BioGro NZ certified and effective Varroa treatment, Thymovar Wafers are thymol based. To control Varroa mites, concentrations of thymol vapor build up to toxic levels, affecting the mites but remains safe for bees. When treating, Thymol vapour concentrations build up in the hive. The vapour is highly toxic to Varroa mites but concentrations are not high enough to harm bees. DO NOT USE where comb honey is to be collected.