Bioactivity of Cinnamomum verum essential oil against Varroa destructor, parasitic mite of Apis mellifera

The honeybee, Apis mellifera (Hymenoptera Apidae) has a great economic and ecological importance. In fact, beside in the beehive products, A. mellifera plays a major role in the pollination of wild angiosperm and crops species, essential for ecosystem functioning and human food production. Varroa destructor (Acari Mesostigmata Varroidae), an ectoparasitic mite, is the most devastating parasite of the Western honeybees and causes substantial losses of colonies worldwide. Currently, the control of this pest mainly relies on chemicals such as oxalic acid, pyrethroids, and organophosphates. However, the extensive and repeated use of acaricides have caused the development of resistance in V. destructor populations, causing a reduction of their efficacy and are toxic to bees. Moreover, these products may leave residues in the hive, contaminating honey and beeswax. For these reasons, the use of alternative strategies for the control of V. destructor are required. Essential oils of aromatic plant are known to have repellent, insecticidal and acaricidal properties [1] and could represent a very valuable low-cost, environmental-friendly alternative to synthetic products [2]. Cinnamomum verum (Lauraceae) J. Presl is an evergreen tropical tree originated in Sri Lanka, traditionally widely used to flavour foods. C. verum bark yields an essential oil containing cinnamaldehyde and eugenol as main constituents that showed important biological activities, such as peripheral vasodilatory, antitumor, antifungal, cytotoxic and antimutagenic as well as insecticidal and insect repellent activities. In this work, cinnamon bark essential oil was extracted, chemically analysed and tested to evaluate its toxic/repellent activity against V. destructor in both laboratory and apiary. Results of laboratory tests showed that C. verum EO is able to cause, at the concentration of 2%, 24h after the treatment, the detachment of 50% of the mites present on adult bees without causing significant mortality of the bees. In the field, C. verum EO was able to reduce V. destructor population up to about 70%. This study indicated that C. verum could be a promising repellent against V. destructor used as an alternative to chemical treatment in integrated pest management strategies in bee colonies.