Optimierung der Anwendung von 'Apilife VAR ' zur Bekämpfung von Varroa jacobsoni Oud in Bienenvölkern

Abstract - Optimization of the use of 'Apilife VAR' to combat Varroa jacobsoni Oud in honey bee colonies
'Apilife VAR' has been developed to combat Varroa jacobsoni in bee colonies. It consists of a Vermiculite plate which is loaded with about 20 g of a mixture of thymol (76%), eucalyptol (16.4%), menthol (3.8%) and camphor (3.8%). The purpose of these tests was to examine the efficiency of the product in the following conditions: a) duration of the treatment: 4 or 8 weeks; b) dosage in Swiss hives: twice 1 plate, twice 1/2 plate or once 1 plate; c) formulation: with or without camphor; d) disposition of the plates in Swiss hives, directly on the brood combs or on a fine-meshed grid positioned on the combs; e) disposition of the plates in Dadant and Ritter hives: directly on the combs (above) or under the bottom grid (below). Problems related with bee toxicity, concentration of the components of the product in the air of the hive and residues in the bee food and honey have also been examined. In the Swiss hive the average efficiency of 'Apilife VAR' was 97.7% after 8 weeks of treatment and 93.7% after 4 weeks of treatment. The difference was not significant. Twice 1 plate was the best dosage in the Swiss hive. The difference of formulation (with or without camphor) did not influence the results of the treatment (table I). The fine-meshed grid between the brood comb and the plate did not change substantially the efficiency of the product as long as the bees did not cover the grid with propolis. In the Dadant and Ritter hives the treatment from below was not efficient enough (table II). The treatment from above had an efficiency of 97.1 % in the Ritter hives and of 89% in the Dadant hives. A method for the estimation of the number of varroas remaining in the colony after application of 'Apilife VAR' is presented. It is based on the correlation (r = 0.867) between the number of dead varroas found on the hive bottom during the first 2 weeks after the 'Apilife VAR' treatment and the number of dead varroas after the subsequent Perizin treatment (fig 1). If less than 1 varroa falls per day, the remaining varroa population will be lower than 100. If this condition is filled no further measures must be taken. 'Apilife VAR' did not influence the mortality of the bees and the development of the colonies. The thymol concentrations of the air of 4 bee colonies varied from 1.1 to 21.3 μg/l. Whereas the values were equilibrated in the Swiss hives, they fluctuated considerably in the Dadant hives (fig 2). The eucalyptol, menthol and camphor concentrations were much lower. They varied between ≤ 0.02 and 2.4 μg/l of air. These concentrations have probably no varroacidal effect. Only thymol residues were detected in the bee food and honey (table III). After 8 weeks of treatment the mean residue values were 2.6 mg/kg (SD ± 2.0, n = 30) in the Swiss hives and 2.0 mg/kg (SD ± 0.98, n = 12) in the Dadant and Ritter hives. The maximum value was 9.2 mg/kg. 8 months later the respective values in the spring honey harvest were 0.1 mg/kg (SD ± 0.09, n = 30) and 0.03 mg/kg (SD ± 0.01, n = 12), with a maximum value of 0.33 mg/kg. The residues found in honey are innocuous to human health. Thymol is generally recognized as safe ('GRAS' status), ie concentrations up to 50 mg/kg are considered unobjectionable. Before making a general assessment of 'Apilife VAR' it will be necessary to carry out further residue measurements and to fix the perception threshold for thymol in different types of honey.