Evaluation of the efficacy of essential oils against Varroa destructor on Apis mellifera macedonica

The improper use of synthetic acaricides has led to the differentiation of resistant varroa populations. With the purpose of developing alternative and environmentally friendly techniques to control Varroa destructor, a study on the biological activity of Geranium robertianum L., Melaleuca leucadendron L. var. cajeputi R. and Lavandula officinalis Chaix essential oils (EOs) was carried out. The study, conducted at the Institute of Apiculture in Nea Moudania (Greece), included in vitro tests on varroa adults and larvae of Apis mellifera macedonica (Rutner), cage trials on adult bees, and field trials on V. destructor. In the in vitro tests, 10 varroa and 10 A. m. macedonica larvae (5 replicates) were used and the EOs were tested at 1.5; 2.0; 2.5; 3.25; 5.0μL/127.17 mL Petri dish. The tests indicated that the maximum mortality of the mites was observed, at different concentrations of the three oils, 21h after their administration. Oxalic acid (OA) induced the highest honeybee larval mortality. The cage trials demonstrated that EOs induced an adult bees mortality not different from that recorded in controls. For the field trials, 20 hives were utilised (5 per EO and 5 mineral oil) and EOs were tested as a 4 ml mineral oil:EO solution (1:1). Results revealed that EOs solutions induced a significantly higher mean mortality of mite than that obtained in the control and comparable to that of OA. Similar results were obtained controlling V. destructor on A. m. ligustica Spinola. EOs could be an effective and sustainable tool to control V. destructor.