Abstract
Varroa destructor mites are a leading cause of honey bee (Apis mellifera) colony losses worldwide. The acaracide amitraz has been among the most preferred Varroa treatments for more than a decade because of its high effectiveness and convenience of application. As a result, over reliance on amitraz has led to Varroa resistance to amitraz. Here, we evaluated U.S. registered Varroa treatments with differing active ingredients on Varroa infestation rates and their impact on amitraz resistant Varroa to identify alternative treatment options for commercial beekeepers just prior to winter, a critical time of year to have low mite infestation. Treatment groups included an untreated Control, Apivar (active ingredient amitraz), FormicPro (a.i. formic acid), HopGuard 3 (a.i. hops β-acids) and Api-Bioxal vapor (a.i. oxalic acid, “OA” Vapor). Treatments were implemented in late September; colonies were assessed in late November and early February, 63 and 133 days later. We found that the Apivar, FormicPro and HopGuard treatment groups maintained Varroa infestation rates, whereas Varroa infestation rates significantly increased in the untreated Control and OA Vapor treatment groups. Genetic analysis showed that the frequency of the amitraz resistance genotype significantly increased from Day 0 to Day 63 after the application of Apivar, but this change was reversed by Day 133 after the overwintering period. Comparatively, the amitraz resistance genotype frequency was not impacted by any other treatment group. This indicates there is no cross-resistance of amitraz to other active ingredients tested, and that amitraz resistance may not have a large fitness cost.
Data availability
Datasets generated from this experiment will be made available upon reasonable request to the corresponding author.
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Acknowledgements
We would like to thank Zachary Beneduci for his assistance with the statistical analysis, and members of the Auburn University Bee Center for field work assistance.
Funding
This work was supported by the Alabama Department of Agriculture and Industries Specialty Crop Block Grant ADAI-PROJ 2-2025, United States Department of Agriculture Agricultural Research Service cooperative agreements 58-6066-9-042 and 58-6066-3-029, United States Department of Agriculture National Institute of Food and Agriculture Specialty Crop Research Initiative grant #2023-51181-41246, Project Apis m. project M-SGA 312, the Alabama Agricultural Experiment Station, and the United States Department of Agriculture National Institute of Food and Agriculture Multi-state Hatch Project NC1173.
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RT: Conceptualization, Formal Analysis, Funding Acquisition, Investigation, Methodology, Visualization, Writing – original draft, Writing – review & editing. FR: Conceptualization, Investigation, Methodology, Resources, Supervision, Writing – original draft, Writing – Reviewing & Editing. DA: Conceptualization, Investigation, Methodology, Writing – review & editing. NE: Investigation, Methodology. KC: Investigation, Methodology. GW: Conceptualization, Funding acquisition, Project administration, Resources, Supervision, Writing – reviewing & editing.
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Tokach, R., Rinkevich, F., Aurell, D. et al. Evaluation of late-season Varroa destructor treatments and their impact on amitraz resistant mite populations. Sci Rep (2026). https://doi.org/10.1038/s41598-026-44796-8
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DOI: https://doi.org/10.1038/s41598-026-44796-8