Evaluation of some essential oils for the control and prevention of American Foulbrood disease in honey bees

American Foulbrood (AFB), caused by the spore-forming bacterium Paenibacillus larvae larvae, is the most serious disease of honeybees. Laboratory and field trials were conducted to evaluate the effectiveness of essential oils from savory, thyme, lemon-grass, and oregano, and blends of lemon-grass + thyme; lemon-grass + thyme + oregano + basil, and lemon-grass + thyme + basil in preventing and controlling infections of AFB in Apis mellifera colonies. The principal components of the essential oils used were determined by gas chromatography. LD50 values for acute oral toxicity of the oils on adult bees verified that the essences were non-toxic or slightly toxic. Results from field trials indicate that neither the essences nor the blends were effective in the elimination of AFB clinical symptoms at any dose formulation or method of administration tested, whereas tylosin was highly effective in eliminating AFB clinical symptoms.