Effects of essential oils on foulbrood bacteria and honey bee workers (Apis mellifera) under laboratory conditions

Introduction: , respectively, and their safety towards bees. Methods: against the two foulbrood bacteria by the spot-on-agar test, where the EOs were deposited directly onto the agar surface. The EOs demonstrating the most significant antimicrobial activity against one or both of the bacterial pathogens were then selected for further assessment of their toxicity towards the foulbrood bacteria by the resuzurin-based microdilution method and towards adult bees using the vapor exposure bioassay at one and three hours. Results: The study revealed that oregano, juniper, sage, thyme, cinnamon, cumin, clove and black pepper were the most effective against the foulbrood bacteria. The results of the exposure bioassays demonstrated that bees exposed to those EOs exhibited greater tolerance to the vapor of cinnamon and oregano after one hour of exposure than the other EOs. As the duration of exposure increased to a period of three hours, an escalation in toxicity was observed. Discussion: larval bioassays and field trials are needed to validate their clinical effectiveness and safety.