Détermination de la DL₅₀ de l'amitraze et du coumaphos sur Varroa jacobsoni Oud au moyen des acaricides Anti-varroa^® (Schering) et Perizin^® (Bayer)

Abstract - Determination of LD₅₀ of amitraz and coumaphos on Varroa jacobsoni Oud by means of Anti-varroa^® (Schering) and Perizin^® (Bayer) acaricides
The occurrence of a resistance phenomenon in Varroa jacobsoni can be shown by comparing the LD₅₀ of an acaricide formula over time. This work proposes a simple method for determining the LD_{5 0} and applies it to 2 compounds: Antivarroa^®(Schering) and Perizin^® (Bayer). Tests were made in polycarbonate boxes which were changed each time. Temperature was 26-28 °C, humidity 70%. Varroa mites were taken from infested bees with a paintbrush and immobilized on a foam-rubber bed. 0.25 ml of an acaricide solution was applied via a microsyringue. The mites were then replaced on the bees. Each box contained 20 infested bees and 10 non-infested bees. Different solutions of the acaricide were tested to determine a toxicity curve and to calculate the LD₅₀ after 24 h by the method of Lichtfield and Wilcoxon (Thalarida and Murry, 1988). The mean LD ₅₀ of Anti-varroa^® was 17.3 pg per varroa (11.7-25.6 pg per Varroa; P < 0.05). The LD₅₀ of amitraz in the product Anti-varroa^® was 2.16 pg per Varroa (1.46-3.2 pg). The mean LD₅₀ of Perizin^® was 98.4 pg per varroa (79.1-122.3 pg per Varroa; P< 0.05). The LD₅₀ of coumaphos in the product Perizin^® was 3.15 pg per Varroa (2.53-3.91 pg). The experimental conditions must be accurate in order to obtain reproducible or comparable results: the area where the acaricide solution is deposited must be precisely defined and the reading time specified. Commercial products were used in this study because excipients may influence the toxicity of the active ingredients. This method, using free Varroa mites on bees is more representative of the actual field conditions than methods using isolated mites.