Efficacy of Different Organic Compounds Against Bee Mite (Varroa destructor Anderson and Trueman) in Honey Bee (Apis mellifera L.) Colonies

In the present study, two organic compounds (thymol and oxalic acid) were used to treat colonies against Varroa destructor with three delivery methods. The compounds were applied alone or in combination and the results were correlated with climatic variables (temperature and humidity). We investigated the efficacy of organic products which were applied as dust, diluted in sugar syrup trickled onto the bees and dissolved in ethanol embedded in vermiculite blocks. The best results were obtained with thymol applied in dust (89.98%) and in vermiculite (77.15%). The lowest efficacies were those of the oxalic acid treatments (<50%). There was a positive correlation between temperature and mite mortality for the thymol in dust and for the thymol in vermiculite methods (r = 0.73 and r = 0.71, respectively). Conversely, a negative correlation was found between humidity and mite mortality for thymol applied in dust (r = -0.71). Mite mortality in oxalic acid treatments did not show significant correlation with climatic variables, except when combined with thymol and applied in vermiculite blocks (r = 0.70). This result indicates that thymol in dust and in vermiculite methods are effective alternative fall treatments for varroa mites.