Effect of selected botanical compounds on Ascosphaera apis and Apis mellifera

Ascosphaera apis is a worldwide spread fungal pathogen that invades the honey bee brood and causes chalkbrood disease. In many countries, its control with fungicides is banned due to residue contamination of bee products and health risk. Since then, there is no alternative treatment. In this study, an antifungal activity of 10 essential oils or their components has been investigated. The agar dilution method showed considerable differences be-tween its antifungal activity with the best results exhibited by thyme oil (MIC50 = 57.7 mu L/L) followed by cedarwood oil (MIC50 = 64.9 mu L/L), thyme (MIC50 = 82.5 mu L/L), clove bud oil (MIC50 = 114.2 mu L/L), and cinnamon oil (MIC50 = 136.6 mu L/L). These botanical compounds have also been tested using a honey bee tolerance by complete exposure method. The oil tolerated the most by honey bees was from cedarwood (LC50 = 33.4 mu L). The composition and quantity of main components of the oils mentioned above were determined by GC-MS/MS. Thymol is responsible for the antifungal activity of thyme oil, whereas, in clove bud and cinnamon oil, the main component is eugenol. Cedarwood oils contain primarily gama and alpha cendrene. The results suggest the analyzed compounds can be used to control multiple honey bee pathogens simultaneously due to their broad spectrum of antimicrobial activity and enhanced efficacy by synergistic effect.