Synthesis and acaricidal activity against Varroa destructor of α- and γ-costic acid dimers

α-Costic acid is a natural sesquiterpene possessing diverse biological activities. Among these, the most promising property for practical application is its acaricidal activity against Varroa destructor, considered the most important and dangerous parasite of the honeybee (Apis mellifera L.). Infestations of V. destructor can decimate bee populations in just a few years, resulting in substantial environmental and economic losses. This study reports the synthesis of α- and γ-costic acid diesters with ethylene glycol and evaluates their acaricidal efficacy against V. destructor in comparison with their parent acids. Although the resulting dimers were approximately 50% less active than the parent costic acids, they exhibited higher potency than the previously reported α-costic acid methyl ester. Among all, γ-costic acid, whose acaricidal activity is reported here for the first time, shows the highest activity with mortality higher than 90%, thus emerging as the most promising candidate for the development of effective and environmentally friendly strategies for the control of V. destructor. Furthermore, it may hold potential for the biocontrol of other mite pests affecting economically important crops such as legumes and cereals, which are currently associated with significant yield losses and extensive reliance on synthetic pesticides.