Why rotation and mixture fail: treatment history and the declining acaricide efficacy in Varroa destructor.

BACKGROUND

Insecticide resistance management (IRM) strategies, such as rotation and mixture, rely on fitness tradeoffs and susceptible population dilution to slow resistance. While IRM is widely recommended, its robustness when a target pest's biology violates these foundational assumptions remains poorly tested. The honey bee parasite, Varroa destructor, provides a test case to evaluate these limits. For instance, V. destructor's obligate sibling mating prevents genetic dilution, resistance mutations appear to carry low fitness costs, and acaricide-absorbing beeswax exerts continuous sub-lethal selection even after treatment ceases. Using this system to validate IRM principles, we asked: (1) Does treatment cessation successfully restore acaricide susceptibility? and (2) Do rotation and mixture strategies effectively maintain high mite mortality when standard IRM conditions are compromised?

RESULTS

We conducted the first meta-analysis of IRM outcomes in V. destructor synthesizing treatment history and efficacy data from 15 studies (nine on rotation, seven on mixtures). Modelling revealed acaricide effectiveness declined by 5.5% per year of active treatment, while sensitivity rebounded by 10.7% per year following treatment cessation. Despite this partial recovery, neither rotation nor mixture strategies were associated with improved mite mortality. Susceptibility rebounds were likely insufficient to restore the near-complete kill rates rotation requires, while progressive efficacy declines undermined the baseline conditions necessary for mixtures.

CONCLUSION

Ultimately, although IRM is the standard recommendation for V. destructor, our findings demonstrate that real-world implementation is unlikely to succeed without treatment-history tracking and prescriptive intervention before widespread resistance is established. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.