Oregano oil is a safe miticide tested in many studies with varying effectiveness. A recent study from Guzman-Novoa and colleagues looked into a novel delivery method of essential oils to honey bee colonies. Electric vaporizers containing oregano oil were installed above the brood chamber of honey bee colonies and ran continuously, achieving 97-98% mite reduction. Other oregano oil delivery methods (soaked cardboard, or strips) were considerably less effective at killing mites.

While running electric vaporizers filled with oregano oil all day long is not a practical solution for most beekeepers, the results with electric vaporizers hold promise for thermal treatment to kill mites. One interesting result is that even when oregano oil release diminished after 2 weeks, the vaporizer treatment continued to effectively control mites. The main reason the vaporizer treatment continued to be effective was because the mites fell earlier and their exponential increase was halted. In addition to that reason, it is worth noting that the vaporizers produced heat, and heating the hive body to 106°F is an effective way to kill mites even without essential oil. It would be interesting to run a treatment with an empty vaporizer or another thermal treatment (for example, Bee Hive Thermal Wraps), to distinguish relative contribution of these two modes of killing mites.