T. Abed et Jd. Delahitte, DETERMINATION OF DL(50) OF AMITRAZ AND CO UMAPHOS ON VARROA-JACOBSONIOUD BY MEANS OF ANTI-VARROA(R) (SCHERING) AND PERIZIN (BAYER) ACARICIDES, Apidologie, 24(2), 1993, pp. 121-128
The occurrence of a resistance phenomenon in Varroa jacobsoni can be s
hown by comparing the LD50 of an acaricide formula over time. This wor
k proposes a simple method for determining the LD50 and applies it to
2 compounds: Anti-varroa(R) (Schering) and Perizin(R) (Bayer). Tests w
ere made in polycarbonate boxes which were changed each time. Temperat
ure was 26-28-degrees-C, humidity 70%. Varroa mites were taken from in
fested bees with a paintbrush and immobilized on a foam-rubber bed. 0.
25 ml of an acaricide solution was applied via a microsyringue. The mi
tes were then replaced on the bees. Each box contained 20 infested bee
s and 10 non-infested bees. Different solutions of the acaricide were
tested to determine a toxicity curve and to calculate the LD50 after 2
4 h by the method of Lichtfield and Wilcoxon (Thalarida and Murry, 198
8). The mean LD50 of Anti-varroa(R) was 17.3 pg per varroa (11.7-25.6
pg per Varroa; P < 0.05). The LD50 of amitraz in the product Anti-varr
oas was 2.16 pg per Varroa (1.46-3.2 pg). The mean LD50 of Perizin(R)
was 98.4 pg per varroa (79.1-122.3 pg per Varroa; P< 0.05). The LD50 o
f coumaphos in the product Perizin(R) was 3.15 pg per Varroa (2.53-3.9
1 pg). The experimental conditions must be accurate in order to obtain
reproducible or comparable results: the area where the acaricide solu
tion is deposited must be precisely defined and the reading time speci
fied. Commercial products were used in this study because excipients m
ay influence the toxicity of the active ingredients. This method, usin
g free Varroa mites on bees is more representative of the actual field
conditions than methods using isolated mites.