Evaluation of formic acid and a thymol-based blend of natural products for the fall control of Varroa jacobsoni (Acari: Varroidae) in colonies of Apis mellifera (Hymenoptera: Apidae)

Formic acid, a thymol-based blend of natural products, and Apistan (tau-fluvalinate) were compared as fall control agents for Varroa jacobsoni Oudemans, a parasitic mite of the honey bee, Apis mellifera L. Mite mortality averaged 99% in colonies receiving Apistan, 70% in those receiving the thymol blend, 51% in those receiving formic acid, and 33% in control colonies. Mite mortality in colonies receiving the thymol blend was higher than in the control colonies. The ratio of the coefficient of variation in mite mortality among colonies in the thymol group to the coefficient of variation among colonies in the Apistan group was 67.15. The corresponding ratio for the formic acid group and the Apistan group was 117.65. These results indicate that Apistan is a more effective and a more consistent control agent than the other treatment formulations used in this study. Mortality was independent of the level of mite infestation for all treatments. Overall, 109.52 +/- 5.777 g (approximate to 43.8%) of a 250-ml formic acid treatment evaporated during the 33-d treatment period, giving an average daily release of 3.32 g of formic acid, well below that required for effective mite control. For the thymol blend, 26.32 +/- 1.298 g (approximate to 65.8%) of the original! 80 g of material evaporated during the treatment period, giving an average of 0.80 g/d. The amount of each material evaporating was positively correlated with ambient temperature. The number of mites collected during the 1st 4 d of the evaluation period was correlated (r = 0.99) with the total number of mites collected during the entire 34-d evaluation period.