Evaluating the seasonal efficacy of commonly used chemical treatments on Varroa destructor (Mesostigmata: Varroidae) population resurgence in honey bee colonies

Abstract

The purpose of this research was to determine how common chemical treatments influence Varroa destructor (Anderson and Trueman) population resurgence rates (defined as time posttreatment for mite populations to reach 3 mites/100 adult bees) in managed honey bee (Apis mellifera L.) colonies seasonally. We conducted 2 experiments that followed the same basic protocol to address this purpose. We established 6 treatment groups in Experiment 1 in the fall of 2014: untreated control, Apivar, Apistan, CheckMite+, ApiLifeVar, and Mite Away II applied to 10 colonies per treatment. In Experiment 2, we applied 8 chemical treatments to each of 4 seasonal (spring, summer, fall, and winter) cohorts of honey bee colonies to determine how mite populations are influenced by the treatments. The treatments/formulations tested were Apivar, Apistan, Apiguard, MAQS, CheckMite+, oxalic acid (dribble), oxalic acid (shop towels), and amitraz (shop towels soaked in Bovitraz). In Experiment 1, Apivar and Mite Away II were able to delay V. destructor resurgence for 2 and 6 months, respectively. In Experiment 2, Apiguard, MAQS, oxalic acid (dribble), and Bovitraz treatments were effective at delaying V. destructor resurgence for at least 2 months during winter and spring. Only the Bovitraz and MAQS treatments were effective at controlling V. destructor in the summer and fall. Of the 2 amitraz-based treatments, the off-label Bovitraz treatment was the only treatment to reduce V. destructor populations in every season. The data gathered through this study allow for the refinement of treatment recommendations for V. destructor, especially regarding the seasonal efficacy of each miticide and the temporal efficacy posttreatment.

Combined treatment with amitraz and thymol to manage Varroa destructor mites (Acari: Varroidae) in Apis mellifera honey bee colonies (Hymenoptera: Apidae)

“…We suspect that beekeepers are more likely to adopt new or optimized registered treatments if they see how these compare against a treatment they have confidence in. Our research as well as that of others in this special issue ( Jack et al 2024 ) demonstrate that amitraz EC can provide higher efficacy or more rapid control than currently registered treatments. This makes it an especially relevant positive control—so that we can develop registered treatments that match or exceed the performance of amitraz EC.…”

“…Some beekeepers also resort to using emulsifiable concentrate formulations of amitraz (hereafter “amitraz EC”; active ingredient, amitraz 12.5%), despite these formulations not being registered for use on honey bees in the United States ( Honey Bee Health Coalition 2021 , Jack and Ellis 2021 ). This is in part because beekeepers anecdotally report more rapid and effective control with amitraz EC than with Apivar, which is consistent with recent findings ( Jack et al 2024 ) and in part because the cost per treatment is low ( Honey Bee Health Coalition 2021 ). To address unregistered product use and the emergence of amitraz-resistant Varroa ( Rinkevich 2020 ), it is pressing to develop registered treatment options that do not rely solely on amitraz, but still control Varroa effectively and rapidly, while being safe for colonies.…”

“…We think it is important for US honey bee researchers to include the unregistered amitraz EC treatment as a positive control when performing tests of alternative treatments against Varroa . As far as we are aware, our study and another study in this issue ( Jack et al 2024 ) are the first peer-reviewed US studies of treatments against Varroa since the late 1980s (e.g., Witherell and Herbert 1988 ) to include amitraz EC, despite it being widely used in the US beekeeping industry ( Honey Bee Health Coalition 2021 ). By providing concrete data on its effects, we not only fill a gap in the literature, but also can communicate our findings on alternative treatments in a way that is more relevant to beekeepers who currently rely on amitraz EC.…”

Current honey bee stressor investigations and mitigation methods in the United States and Canada

“…These findings may allow beekeepers to decrease the selection pressure on Varroa that has led to resistance ( Rinkevich 2020 ), although the resulting drop in bee population after combined treatments calls for further study. Jack and colleagues ( 2024 ) evaluated various Varroa control methods in Florida, finding seasonal variations of efficacy for the 8 methods tested. Interestingly, treatments that delayed Varroa resurgence for 2–6 months in the winter and spring were not all effective when applied in the summer and fall.…”