Microencapsulation of Carvacrol in Alginate–CMC Matrices as a Controlled-Release and Biocompatible Strategy for the Control of Varroa destructor

Varroa destructor is the primary threat for honeybees due to the damage that it causes at both individual and colony levels. While numerous synthetic miticides have been employed to combat varroa infestations, there is a growing recognition of the importance of utilizing natural compounds, such as phytochemicals. With emerging interest, natural treatments based on Essential Oils extracted from aromatic plants as different species of Origanum or Thymus have evolved as a promising therapeutic tool against the ectoparasitic mite Varroa destructor of honeybee ( Apis melifera ) colonies. Carvacrol has demonstrated high efficacy in causing mortality among varroa mites but its impact on honeybees remains unclear. Encapsulation technology can be used to improve the stability, safety and biological activity of Carvacrol in environmental conditions. In this work, Carvacrol (CRV) was incorporated in microcapsules as the core material and different blends of calcium alginate (ALG) and carboxymethyl cellulose (CMC) was used as the wall material for encapsulation. An experimental design was used to determine the effect of encapsulation and the concentration of cross-linking agent on the behavior of the formulation in terms of sphericity, shell thickness, encapsulation efficiency, and essential oil delivery rate of the microcapsules. The optimized preparation process was obtained through the response surface method. Microcapsules obtained by an encapsulator device based on jet vibration were spherical, with a particle size distribution of 3.5 ± 4.04 mm and an efficiency of encapsulation for carvacrol of 88.75 ± 2.84 %. The in vitro sustained release was nearly zero-order profile, and its cytocompatibility was tested in epidermal human cells. In order to further investigate the practical translation of carvacrol and the optimized formulation against varroa mite infestation, in vivo assays were performed to test the biological compatibility and toxicity of CRV and CRV-loaded microcapsules and in the presence of Apis melifera. Overall, the results confirm that the optimized CRV-loaded microcapsules combine high encapsulation efficiency, controlled release, and biocompatibility, supporting their suitability as a novel, safe and efficient delivery platform with strong potential for innovative anti-Varroa treatments in beekeeping.