Efficacy of apilife var® and thymovar® against varroa destructor as an autumn treatment in a cool climate

The relationship between Varroa destructor and its European honey bee host, Apis mellifera is such that colony mortality is inevitable if mite populations are not controlled. Although in the past, synthetic pyrethroids and organophosphates were used effectively, mite resistance has developed, and today beekeepers are relying more on thymol-based products such as Apilife Var® and Thymovar®. These products, although toxic to the mite are known to show high variability in efficacy under field conditions, as ambient temperatures > 15°C are essential for the evaporation of the active ingredient thymol. To assess their efficacy as an autumn treatment, in cool temperate climates such as Ireland, a field trial was carried out in 2009. A total of 26 colonies were standardised for brood area, and treatments were administered on 21 August following the manufacturers' instructions. To estimate the percentage efficacy of the test treatments, oxalic acid was administered as a winter treatment on 11 December. Thymovar®, with a mean percentage efficacy of 84.7% was more effective than Apilife Var® (53.8%). Natural mite mortality during the test period was approximately 17.8%. An apparent negative impact of the treatments on colony development is discussed with special reference to bee population, brood area and bee mortality.