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Volume 32, Number 1, January-February 2001
Page(s) 49 - 55
DOI: 10.1051/apido:2001110

Apidologie 32 (2001) 49-55

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

Massimo Spreafico, Francesca Romana Eördegh, Iris Bernardinelli and Mario Colombo

Istituto di Entomologia agraria, Milano University, Via Celoria 2, 20133 Milano, Italy

(Received 5 May 2000; revised 19 September 2000; accepted 28 September 2000)

The susceptibility of four populations of Varroa destructor to the organophosphorous acaricide coumaphos was studied. The mites were taken from apiaries kept in Lombardy (northern Italy) and tested with a laboratory assay on paraffin wax with known concentrations of coumaphos. The susceptibility of two populations to coumaphos was close to that of susceptible populations, indicated in the literature (LC50 at 24 hours: 12.6 $\mu$g/g); a third population showed a significant, but slight increase in tolerance (LC50 at 24 hours: 29 $\mu$g/g) while the fourth population had a much higher LC50 (>200 $\mu$g/g at 24 hours). In subsequent field trials carried out in the apiary in which the latter population had been sampled, the total average efficacy of two treatments with Perizin® (the commercial formulation of coumaphos) in colonies without capped brood was 46% (28-88% ).

Key words: coumaphos / Varroa destructor / resistance / bioassay / field trial

Correspondence and reprints: Massimo Spreafico
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© INRA, EDP Sciences, DIB, AGIB 2001