Persistence and effectiveness of pyrethroids in plastic strips against Varroa jacobsoni (Acari : Varroidae) and mite resistance in a mediterranean area

An apiary trial was conducted in 1997 in Sardinia, Italy, to verify the eff ectiveness of fluvalinate in polyvinyl chloride strips and flumethrin in po lyethylene strips against Varroa jacobsoni Oudemans. Two indices to evaluat e the efficacy of the treatments were adopted: percentage change in mite in festation of worker-sealed brood cells considering only treated hives and p ercentage change in mite mortality, and the natural variation in mite popul ations recorded in control hives during the trial. All acaricide treatments reduced the level of mite infestation of both sealed brood and adult bees. However, their effectiveness was slightly reduced in comparison to previou s studies because of mite resistance phenomena. Portions of polyethylene st rips of flumethrin from treated hives were sampled weekly to determine acar icide persistence using gas chromatography. After 4 wk, a slight reduction (approximate to9%) of the active ingredient content was observed, A laborat ory bioassay also was performed to establish the resistance of adult female mites to fluvalinate, Mites were sampled from the experimental apiary and from various Sardinian apiaries which had primarily been subjected to fluva linate applications in plastic strips or wood inserts for years. Mite resis tance varied from 0 to 96%, depending on the acaricide management adopted, The lowest resistance level occurred in an apiary where pyrethroids had nev er been used, whereas the highest level occurred in an apiary with intensiv e use of fluvalinate in wood inserts.