Toxicity of destruxins against the parasitic mite Varroa destructor and its host Apis mellifera

The parasitic mite Varroa destructor Anderson & Trueman (Acari: Mesostigmata) is the most challenging honey bee (Apis mellifera L.) pest for beekeepers worldwide. Studies involving the use of entomopathogenic fungi for control of mite populations have shown that there is potential for their use, but there are several obstacles to their direct application in the hive. One of the promising fungi is Metarrhizium anisopliae, which produces toxins involved in pathogenicity named “destruxins” (Dtx). In this study, we performed trials to evaluate the toxicity of crude and purified Dtx (fractions A, B, CE and D) towards V. destructor and A. mellifera. Mortality of mites treated with crude Dtx and Dtx B and CE was higher than control mites in all performed trials, in which several solvents and administration modes were employed. When purified Dtx B and CE were administered to honey bees at the higher concentration they caused a significantly higher mortality compared to control, showing the need for further research.