Assessment of Four Plant-Derived Extracts as Potential Control Agents Against Varroa destructor with Safety Evaluation in Honey Bees (Apis mellifera)

Abstract

This study evaluated the acaricidal efficacy of extracts from Salvia officinalis (SO), Marrubium vulgare (MV), Ruta graveolens (RG), and Opuntia ficus-indica (OFI) against Varroa destructor, together with their acute toxicity to Apis mellifera. The extracts were characterized for their phenolic content and antioxidant activity. Honey bee toxicity was assessed at 0.5, 1, and 2 mg/mL using three application methods, while acaricidal activity was determined by the drip method. Survival data were analyzed using Kaplan–Meier, the log-rank test, and Abbott’s correction. The extracts differed markedly in their phenolic composition, with RG showing the highest total phenolic content, whereas all extracts exhibited strong antioxidant activity. Toxicity assays revealed significant differences among plant species. SO was the most toxic to honey bees, particularly following drip application, whereas MV and OFI caused minimal mortality. RG showed moderate toxicity that varied with the application method. In contrast, all extracts achieved complete mortality of V. destructor within 4 h, with corrected efficacy exceeding 89%. MV and OFI exhibited the lowest LC50 values, indicating the greatest acaricidal potency. Overall, MV and OFI emerged as the most promising candidates, combining high efficacy against V. destructor with low toxicity to honey bees. However, further validation under field conditions is required.