Evaluation of the efficacy of promising compounds for the control of Varroa destructor and their toxicity to honey bees (Apis mellifera)

Varroa destructor is widely recognized by beekeepers as one of the most significant threats to honey bee (Apis mellifera) health. Decades of research have demonstrated the impact that V. destructor has on honey bee colony losses. Infestation by these mites weakens colonies, often leading to their demise within three or four seasons if no treatment is performed. To control V. destructor, beekeepers currently use a variety of tools, including synthetic acaricides, natural acaricides and management practices. Historically, compounds such as tau-fluvalinate and coumaphos were effective for controlling the mite, however, resistance has developed over time. More recently, amitraz is a commonly used and effective miticide, but there have been reports of emerging reports of resistance to this compound as well. This underscores the continually need for developing new acaricides that are safe for both the honey bee colonies and beekeepers.Our primary objective with this work was to screen new chemicals with acaricidal properties that has the potential to control V. destructor and evaluating their safety to honey bees. Herein, we evaluated the efficacy of four compounds by measuring the dose that was lethal to 50% of V. destructor (LD₅₀) as well as 50% of honey bee adults and larvae. We compared the LD₅₀s of pyridaben, fenpyroximate, fenazaquin and carbamate 421 through topical application to V. destructor and both topical and oral exposure to honey bee adults and larvae.