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

Abstract

Summary — 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 (LC 90 /LC 10 ∼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 LC 50 to coumaphos of mites resistant to pyrethroids was noted. Varroa strains resistant to these acaricides were not studied.

Activity of oxalic and citric acids on the mite Varroa destructor in laboratory assays

“…The ratio between the width of the 95% fiducial interval of the LDe 50 and the LDe 50 was comparable with that obtained with fluvalinate (Milani, 1995), but larger than that with coumaphos (Milani and Della Vedova, 1996). However, to achieve such a ratio, which is indicative of the "precision" of the assay, about twice as many mites were needed.…”

“…Variability does not depend uniquely on the error on the amount of substance deposited, but might be caused also by the different sensitivity of different parts of the body of the mite; e.g., mites laying on their back on the treated surface often showed lesser signs of injury. Mites from different brood stages showed a different sensitivity to oxalic acid, as observed with organophosphorous acaricides (Milani and Della Vedova, 1996). The doses toxic to V. destructor tare comparable with those effective in field treatment by spraying (Imdorf et al, 1995).…”

“…The mortality in the controls was higher than in assays with paraffin wax coated capsules, developed for pyrethroid and organophosphorous acaricides (Milani, 1995;Milani and Della Vedova, 1996). The causes of the increase in natural mortality Table VI.…”

“…The availability of data on the toxicity of coumaphos to mites from untreated populations (Milani and Della Vedova, 1996) has made it possible to detect resistance to this organophosphorous acaricide (Spreafico et al, 2000), before bee losses were reported. On the other hand, little is known of the mode of action of oxalic acid, in particular, why a solution of oxalic acid and sucrose, applied by tricking (Mutinelli et al, 1997), is more effective than a solution of the acid alone, used in the same way.…”

First detection of strains of Varroa destructor resistant to coumaphos. Results of laboratory tests and field trials

“…The spread of Varroa destructor Anderson and Trueman 2000 mites resistant to fluvalinate (Lodesani et al, 1995) caused serious losses to beekeeping in Italy (Astuti et al, 1995) and other countries (Eischen, laboratory (Milani, 1995;Milani and Della Vedova, 1996) are a suitable tool to achieve this objective. With this purpose, in 1999 we started a survey of V. destructor populations taken from colonies in Lombardy (northern Italy) to verify their susceptibility to coumaphos in the laboratory and to test the efficacy of Perizin ® (the commercial formulation of coumaphos) in the field.…”