Three slow release experimental rotenone formulations were tested to evaluate their effectiveness against Varroa destructor Anderson & Trueman in colonies with sealed brood and to determine whether they left residues in honey and bees wax: we evaluated cardboard strip containing 1 g rotenone and two types of polyvinyl chloride (PVC) strips containing 1 (high-dose) and 0.5 (low-dose) g of rotenone, respectively. In general, the efficacy of the treatments, expressed as percentage of mite mortality, was highly variable in all treatment groups (range, 0–96.8%). The highest effectiveness was obtained with the high-dose-PVC strips, which caused an average percentage of mortality ranging between 47 and 69% in the adult bees and sealed brood, respectively. At the end of the treatment, rotenone residues ranged between 0.03 and 0.06 and 1.5–144.0 mg/kg in honey and wax, respectively. Rotenone residues in wax were still detectable 4 mo after the treatment period, whereas no residues were found in honey. The higher residues content and persistence recorded in wax samples, was probably due to the lipophilic nature of rotenone. A reduction in the amount of adults was recorded for the group treated with high-dose-PVC strips compared with the untreated colonies. Toxicological risks connected with the use of rotenone and the low maximum level recently fixed by European legislation (0.01 mg/kg) suggest that rotenone is not a good candidate for reducing varroa populations in honey bee colonies.
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Vol. 101 • No. 4