Apidologie 33 (2002) 417-422
Decline in the proportion of mites resistant to fluvalinate in a population of Varroa destructor not treated with pyrethroidsNorberto Milani and Giorgio Della Vedova
Università di Udine, Dipartamento di Biologia applicata alla Difesa delle Piante, Via delle Scienze 208, 33100 Udine, Italy
(Received 17 January 2002; revised 7 April 2002; accepted 15 April 2002)
The reversion of resistance to pyrethroids in Varroa destructor Anderson & Trueman was studied in Friuli (northern Italy), where resistance was detected in 1995 and pyrethroids had not been used since. Mites were sampled in seven localities each year between 1997 and 2000 and assayed in the laboratory for the resistance to fluvalinate by using paraffin coated capsules. Survival at the diagnostic concentration, expected to kill all susceptible mites (200 mg/kg), decreased in all the localities by about ten times in three years, from 19-66% to 1.3-7.8%. Thus, the disadvantage associated with the resistance to pyrethroids in V. destructor is small, as usual when resistance is due to monooxygenases. Its impact on the selection of resistant mites during annual application of treatments is negligible; appreciable effects of reversion can be expected only over many generations of the mite.
Key words: Varroa destructor / reversion / resistance / pyrethroids
Correspondence and reprints: Norberto Milani
© INRA, EDP Sciences, DIB, AGIB 2002