Major Honey Bee Diseases and Possibilities to Control Them with Essential Oils.

Honeybee colonies are affected by bacterial, fungal, viral, microsporidian, and parasitic diseases that impair brood viability, adult survival, productivity, and beekeeping sustainability. Conventional control relies on sanitary measures, antibiotics where permitted, and synthetic acaricides, but these approaches are constrained by residues, resistance, regulation, and variable field performance. This narrative review critically evaluates essential oils as alternative or complementary tools against American foulbrood, European foulbrood, varroosis, nosemosis, chalkbrood, and mite-associated viral pressure. Evidence indicates that thymol, carvacrol, eugenol, cinnamaldehyde, and related constituents can show marked antibacterial, antifungal, acaricidal, antioxidant, and host-supportive activity under controlled conditions. However, most bacterial, fungal, and nosemosis data remain laboratory-based, and direct antiviral applications against honeybee viruses are not field validated. The strongest practical evidence concerns thymol-based control of Varroa destructor, where efficacy depends on formulation, release rate, temperature, colony status, and safety margins. Essential oils should therefore be considered components of integrated honeybee health management, not substitutes for established measures. Future studies should prioritize chemical standardization, dose-response testing, colony-level trials, brood and queen safety, sublethal behavior and physiology, gut microbiota, residues, and reproducible delivery systems.