Evaluation of the toxicity of carvacrol in Apis mellifera honeybees and its efficacy as an anti-varroa treatment: In vitro study.

Abstract

Varroa destructor is an ectoparasite distributed worldwide and it has become the main threat against beekeeping. Traditionally, synthetic ascaricides with a high risk of developing varroa resistance have been used to treat the disease. In recent years, resistances have been detected in this type of drugs, among other harmful side effects, such as the presence of residues in the hives and their products. Alternative treatments have emerged in response to this problem. Some of this alternative are organic acids, being essential oils the most promising of this group. Some essential acids are already used in beekeeping, like thymol or formic acid. Others are being investigated, such as carvacrol, which is a component extracted from Origanum vulgare essential oil. In this study, we evaluated the mortality rates associated to the application of this essential oil in adult honeybees and its effiectiveness against Varroa destructor. This evaluation was carried out for two different application methods under laboratory conditions; carvacrol-loaded microcapsules and essential oil supplemented in the diet. It was observed that mortality was reduced in the groups treated with microcapsules and in the groups treated at low doses of the oil in the diet. However, groups treated with high doses of oil in the diet presented higher mortality rates. The effectiveness against varroa of the oil-in-diet groups was demonstrated under laboratory conditions.