Toxizität von Thymol, Campher, Menthol und Eucalyptol auf Varroa jacobsoni Oud und Apis mellifera L im LabortestA. Imdorf, V. Kilchenmann, S. Bogdanov, B. Bachofen and C. Beretta
Forschungsanstalt für Milchwirtschaft, Sektion Bienen, CH-3097 Liebefeld, Schweiz
Abstract - Toxic effects of thymol, camphor, menthol and eucalyptol on Varroa jacobsoni Oud and Apis mellifera L in a laboratory test
To study the toxic effects of volatile substances on Varroa and bees, the following test was developed. Two cages (Liebefeld type) with each 100 bees and 20 to 40 Varroa were placed in a desiccator and exposed to air contaminated with the volatile substances. Different air concentrations were produced by admixing fresh air (500 ml/min) to contaminated air (5-130 ml/min depending on the active compound and the desired concentration). This treatment was performed in an incubator at a temperature of 32°C and 50 to 60% relative humidity. After 24, 48 and 72 h, the concentrations of the active compounds in the desiccators were measured. Depending on the active compound and the concentration, 1 to 20 I of air were sucked through adsorbent tubes (Orbo-10, Supelco). Thereafter, the active compounds were washed out with toluene and the extract analysed by gas chromatography. The values of the three air samples gave an average air concentration per treatment. One of 5 desiccators received fresh air only (550 ml/min) and served as a control. After 72 h, dead bees and Varroa were counted. The living bees were numbed with CO2, washed in alcohol to seperate remaining Varroa from their hosts and the mites and bees counted. Varroa and bee mortality was expressed as the percentage of animals found dead during the treatment in the desiccator. The air concentration which killed nearly 100 % of Varroa without noticeable loss of bees was found to be between 5 and 15 μg/l for thymol (fig 1a), between 50 and 150 μg/l for camphor (fig 1b) and between 20 and 60 μg/l air for menthol (fig 1c). 240 μg/l eucalyptol produced 100% Varroa mortality but also 25% bee mortality (fig 1d). Thymol was found to be efficient as main compound of the varroacid "Apilife VAR" in different types of hives. Camphor and menthol also possess the necessary characteristics of an efficient varroacid. Eucalyptol however, is not very suitable for Varroa treatment since its rate of evaporation is difficult to control and only a small difference between its toxicity for Varroa and for bees was observed.
Key words: Apis mellifera / Varroa jacobsoni / volatile oil / toxicity / chemical control