D3039: Evaluating the toxicity of known honey bee-safe insecticides in controlling small hive beetles (Aethina tumida)

Currently, there are no effective chemical controls against A. tumida, a widespread honey bee (Apis mellifera) pest, due to resistance against active ingredients, such as coumaphos. In order for new treatments to be used in the hive, they need to be simultaneously toxic to A. tumida and relatively safe for honey bees. In this study, we tested acetamiprid, chlorantraniliprole, flubendiamide, propiconazole and thiacloprid as possible active ingredients, which have been shown in previous studies to demonstrate low toxicity towards honey bees. To test their toxicities, we treated both A. tumida and honey bees topically and also exposed A. tumida to these compounds orally via pollen. We used coumaphos (industry standard), a solvent control (acetone) and a positive control (dimethoate) for comparisons. Thiacloprid (LD₅₀ = 1.27 ng/beetle; LC₅₀= 249.3 µg/ml) was the most toxic active ingredient tested against A. tumida both topically and through pollen. Topically, thiacloprid was 340× more toxic to A. tumida than coumaphos (LD₅₀ = 431.4 ng/beetle). However, when compared with the toxicity to honey bees, acetamiprid (selectivity ratio = 447) was much more toxic to A. tumida than to honey bees than was thiacloprid (selectivity ratio = 3). Coumaphos, the only labeled chemical treatment is 6× more toxic to honey bees than A. tumida. These findings demonstrate that acetamiprid has the greatest potential to reduce A. tumida populations safely in a honey bee colony. Field research should be conducted to further understand the potential of acetamiprid as viable treatment option and to explore possible sub-lethal effects.