Detection of amitraz resistance and reduced treatment efficacy in the Varroa Mite, Varroa destructor, within commercial beekeeping operations

Abstract

The parasitic mite Varroa destructor and the associated viruses it transmits are responsible for most instances of honey bee colony losses in the United States. As such, beekeepers utilize miticides to control Varroa populations. Widespread resistance has developed to the miticides fluvalinate and coumaphos. However, Varroa has largely maintained susceptibility to amitraz despite a long and extensive use history. Anecdotal reports of reduced amitraz effectiveness have been a widely discussed contemporary issue among commercial beekeepers. Amitraz resistance was measured by in vitro bioassays with technical amitraz as well as Apivar ® efficacy tests. Amitraz resistance was evaluated in commercial beekeeping operations in Louisiana, New York, and South Dakota with a long history of amitraz use. This research shows that amitraz remains an effective Varroa control product in many operations. However, apiaries across operations displayed a wide range of amitraz resistance from no resistance to high resistance that resulted in Varroa control failure. The resistance ratios from in vitro amitraz bioassays were correlated with reduced Apivar ® efficacy, demonstrating bona fide cases of Varroa control failures due to amitraz resistance. Therefore, amitraz resistance monitoring protocols need to be developed. A resistance monitoring network should be established to ensure the sustainability of miticide use for Varroa control.

Evaluation of potential miticide toxicity to Varroa destructor and honey bees, Apis mellifera, under laboratory conditions

“…Apivar has been used in Canada for more than a decade and remains an effective option for beekeepers. This product has been registered in the USA since 2013, and recently Rinkevich 12 reported resistance of Varroa mites to amitraz in Louisiana, New York, and South Dakota beekeeping operations. However, in this study, amitraz efficacy was > 90% at dilution of > 10 mgL −1 indicating that amitraz remains an effective product for the control of V. destructor in the tested mite population.…”

“…Synthetic Varroacides, such as pyrethroids, organophosphate and formamidine, have been used to control Varroa mite populations globally, since the 1980's. The long-term use of these products has led to the development of resistance in mite populations, the accumulation of residues in bee products, and an increased risk to human health [11][12][13] . Currently, populations of Varroa mites globally have developed resistance to the pyrethroid, Apistan (824 mg of tau-fluvalinate/strip, Vita Europe), and to the organophosphate, Checkmite (1300 mg coumaphos/strip, Bayer) 1 .…”

“…Currently, populations of Varroa mites globally have developed resistance to the pyrethroid, Apistan (824 mg of tau-fluvalinate/strip, Vita Europe), and to the organophosphate, Checkmite (1300 mg coumaphos/strip, Bayer) 1 . Additionally, resistance is emerging to the only remaining viable formamidine miticide, Apivar (500 mg of amitraz/strip, Veto Pharma) 12 . This new reality highlights the need for alternative synthetic products with different modes of action, which would support an integrated approach to the management of mites and maintenance of healthy bees.…”

Large-scale monitoring of resistance to coumaphos, amitraz and pyrethroids inVarroa destructor

“…Currently, the extensive use of amitraz is exerting an intense selection pressure over populations, threatening them with the evolution of resistance to this compound. Indeed, a reduction in the efficacy of amitraz for Varroa control, probably associated with the evolution of resistance, has already been reported elsewhere (Rodríguez-Dehaibes et al 2005, Maggi et al 2010, Kamler et al 2016, Rinkevich 2020).…”

Mutations associated with pyrethroid resistance in Varroa mites, a parasite of honey bees, are widespread across the USA

“…As with other arthropod pests, intensive treatment schemes that rely exclusively on a single compound over consecutive seasons has resulted in the evolution of resistance in mite populations [35][36][37][38][39] . Currently, resistance to the three classes of synthetic compounds used for Varroa control has been reported 37,[40][41][42] .…”