Determination of the LC₅₀ in the mite Varroa jacobsoni of the active substances in Perizin^® and Cekafix^®

Abstract - A bioassay has been developed to measure the toxicity of the organophosphorus acaricides, the active ingredients of Perizin^® and Cekafix^®, to the mite Varroa jacobsoni Oud. The distribution of the lethal concentrations was rather narrow (LC₉₀/LC₁₀~4). Slight, but significant and consistent differences (up to three times) were found among groups of mites taken from different brood stages; at 26 °C the toxicity was 1.2-2.7 times lower than at 32.5 °C; at a given concentration coumaphos was about twice as active as the active ingredient of Cekafix^®. No increase in the LC₅₀ to coumaphos of mites resistant to pyrethroids was noted. Varroa strains resistant to these acaricides were not studied.