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 concen trations were produced by admixing fresh air (500 ml/min) to contamina ted air (5-130 ml/min depending on the active compound and the desired concentration). This treatment was performed in an incubator at a tem perature of 32-degrees-C and 50 to 60% relative humidity. After 24, 48 and 72 h, the concentrations of the active compounds in the desiccato rs were measured. Depending on the active compound and the concentrati on, 1 to 20 l of air were sucked through adsorbent tubes (Orbo-10, Sup elco). Thereafter, the active compounds were washed out with toluene a nd 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 cont rol. After 72 h, dead bees and Varroa were counted. The living bees we re numbed with CO2, washed in alcohol to seperate remaining Varroa fro m their hosts and the mites and bees counted. Varroa and bee mortality was expressed as the percentage of animals found dead during the trea tment 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 mug/l for thymol (fig 1a), between 50 and 150 mug/l for campho r (fig 1b) and between 20 and 60 mug/l air for menthol (fig 1c). 240 m ug/l eucalyptol produced 100% Varroa mortality but also 25% bee mortal ity (fig 1d). Thymol was found to be efficient as main compound of the varroacid ''Apilife VAR'' in different types of hives. Camphor and me nthol also possess the necessary characteristics of an efficient varro acid. Eucalyptol however, is not very suitable for Varroa treatment si nce its rate of evaporation is difficult to control and only a small d ifference between its toxicity of Varroa and for bees was observed.