LAUSR

Abstract BACKGROUND The Varroa mite (Varroa destructor) is an ectoparasite that can affect the health of honey bees (Apis mellifera) and contributes to the loss of colony productivity. The limited availability of Varroacides with different modes of action in Canada has resulted in the development of chemical resistance in mite populations. Therefore, an urgent need to evaluate new potential miticides that are safe for bees and exhibit high efficacy against Varroa exists. In this study, the acute contact toxicity of 26 active ingredients (19 chemical classes), already available on the market, was evaluated on V. destructor and A. mellifera under laboratory conditions using an apiarium bioassay. In this assay, groups of Varroa‐infested worker bees were exposed to different dilutions of candidate compounds. In semi‐field trials, Varroa‐infested honey bees were randomly treated with four vetted candidate compounds from the apiarium assay in mini‐colonies. RESULTS Among tested compounds, fenazaquin (quinazoline class) and fenpyroximate (pyrazole class) had higher mite mortality and lower bee mortality over a 24 h exposure period in apiariums. These two compounds, plus spirotetramat and spirodiclofen, were selected for semi‐field evaluation based on the findings of the apiarium bioassay trials and previous laboratory studies. Consistent with the apiarium bioassay, semi‐field results showed fenazaquin and fenpyroximate had high efficacy (>80%), reducing Varroa abundance by 80% and 68%, respectively. CONCLUSION These findings suggest that fenazaquin would be an effective Varroacide, along with fenpyroximate, which was previously registered for in‐hive use as Hivastan. Both compounds have the potential to provide beekeepers with an alternative option for managing Varroa mites in honey bee colonies. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.