Toxicity and colony-level effectiveness of essential oils for the management of Varroa destructor and Tropilaelaps clareae in co-infested Apis mellifera colonies

Parasitic mites of Apis mellifera, particularly species belonging to the genera Varroa and Tropilaelaps, commonly co-occur in honey bee colonies, posing challenges to beekeepers in achieving effective colony management. The present study evaluated the toxicity and hive-based efficacy of four essential oils against Varroa destructor and Tropilaelaps clareae in Apis mellifera colonies co-infested with both mite species. In laboratory fumigation bioassays, thyme oil proved to be the most toxic against both mite species, with median lethal concentrations (LC₅₀) of 3.85 and 3.19 µl/l air, respectively. The selectivity ratio for A. mellifera was also highest for thyme oil, followed by eucalyptus, clove, and lemongrass oils. In colony examinations, all tested oils were effective in reducing the infestation of both mite species compared to the control, although variable responses were observed among the essential oils. For all tested oils, efficacy was higher against V. destructor and lower against T. clareae after treatment. A significant increase in brood area was observed in colonies treated with thyme oil, indicating its safety and adaptability to honey bees, whereas the other oils showed non-significant effects. Overall, the findings suggest that the selected essential oils can provide effective control of parasitic mites with acceptable safety to honey bees, highlighting their potential for inclusion in integrated mite management strategies.