Effectiveness, persistence, and residue of amitraz plastic strips in the apiary control of Varroa destructor

An apiary trial was conducted in 1999 in Northern Sardinia (Italy) to evaluate the effectiveness and the persistence of amitraz impregnated in plastic strips against Varroa destructor Anderson and Trueman. Twelve colonies of bees derived from Apis mellifera ligustica Spin. in Dadant Blatt hives were used; six colonies were treated with 2 strips per hive and the other six were left untreated control. Two methods for the evaluation of treatment efficacy were compared: The percent effectiveness measured as the percent reduction of V. destructor infestation in treated hives, and the percent control which took into consideration natural mortality in the control hives. Percent effectiveness was greater than the percent control. Amitraz residues were determined in honey and the plastic strips. No amitraz residue higher than 0.01 mg·kg-1 was detected in honey. The amitraz content was stable during the trial in plastic strips placed in the colonies, and in the control strips. A higher adult bee mortality in the treated hives was recorded only after the first week of the treatment.