Microcalorimetric investigation of the action of propolis on Varroa destructor mites

Treatment of Varroa destructor (Anderson and Trueman) mites with propolis has displayed both narcotic and lethal effects. The length of narcosis and rate of mortality showed dependence on the concentration of propolis used, the duration of contact time and the extraction procedure. Investigation of the action of propolis on the heat production rate of Varroa mites was performed by means of a Biocalorimeter (BCP 600). Calorimetric results point to the fact that even weak propolis concentrations with feeble lethal effects have a strong influence on the specific heat production rate. Thus, treatment with a 20% propolis solution in 40% ethanol resulted in a mortality rate of only 34% but dropped the heat production rate by 75%, a corresponding 5% propolis solution had no lethal effect but reduced the specific heat production rate still by 37% and treatment with a 0.5% propolis solution in 55% ethanol resulted in a non-significant mortality rate of 7% but reduced the specific heat production rate by 29%. Propolis showed a strong impact on the structure of the calorimetric power–time (p–t) curves. The usually highly structured p–t curves were smoothed due to treatment even with weak propolis concentrations.