Essential Oils for a Sustainable Control of Honeybee Varroosis

SIMPLE SUMMARY: The western honeybee (Apis mellifera L.) is one of the most valuable insect species. However, several biological stressors pose a threat to this pollinating insect. Among these, the ectoparasitic mite Varroa destructor is currently the most significant concern. In this paper, we offer an updated analysis of the literature on the use of essential oils (EO) to fight against V. destructor. Numerous aromatic plants have been subjected to EO extraction to test their varroacidal efficacy in the laboratory or in the field. The results were extremely different even when the same botanical species were used in independent studies. This is undoubtedly related to the enormous variety of methods used to assess the efficacy of acaricides and the variation in plant composition according to origin. This review, in addition to providing an overview of the results, seeks to steer the scientific community towards consistent evaluation methods by pointing out the most valuable research projects currently underway. ABSTRACT: The Varroa destructor parasite is the main obstacle to the survival of honey bee colonies. Pest control mainly involves the use of synthetic drugs which, used with the right criteria and in rotation, are able to ensure that infestation levels are kept below the damage threshold. Although these drugs are easy to use and quick to apply, they have numerous disadvantages. Their prolonged use has led to the emergence of pharmacological resistance in treated parasite populations; furthermore, the active ingredients and/or their metabolites accumulate in the beehive products with the possibility of risk for the end consumer. Moreover, the possibility of subacute and chronic toxicity phenomena for adult honeybees and their larval forms must be considered. In this scenario, eco-friendly products derived from plant species have aroused great interest over the years. In recent decades, several studies have been carried out on the acaricidal efficacy of plant essential oils (EOs). Despite the swarming of laboratory and field studies, however, few EO products have come onto the market. Laboratory studies have often yielded different results even for the same plant species. The reason for this discrepancy lies in the various study techniques employed as well as in the variability of the chemical compositions of plants. The purpose of this review is to take stock of the research on the use of EOs to control the V. destructor parasite. It begins with an extensive discussion of the characteristics, properties, and mechanisms of action of EOs, and then examines the laboratory and field tests carried out. Finally, an attempt is made to standardize the results and open up new lines of study in future.