from:
Apidologie 32 (2001) 49–55 49
© INRA/DIB-AGIB/EDP Sciences, 2001

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

by Massimo SPREAFICO*, Francesca Romana EÖRDEGH, Iris BERNARDINELLI, Mario COLOMBO
Istituto di Entomologia agraria, Milano University, Via Celoria 2, 20133 Milano, Italy

Abstract –
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 (LC 50 at 24 hours: 12.6 mg/g); a third population showed a significant, but slight
increase in tolerance (LC 50 at 24 hours: 29 mg/g) while the fourth population had a much higher
LC 50 (>200 mg/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%).


submitted by
Peter Borst
Ithaca NY U S A