Timing of acaracide treatments for control of low-level populations of Varroa destructor (Acari: Varroidae) and implications for colony performance of honey bees

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AbstractThe timing of acaracide treatments for control of low-level populations of Varroa destructor Anderson et Trueman has implications for colony performance of honey bees, Apis mellifera L. (Hymenoptera: Apidae). Replicated colonies with low levels of V. destructor were left untreated, exposed to fluvalinate at each of two doses for 42 days, or exposed to three applications of formic acid, with the four treatments applied in either spring or fall. Varroa destructor densities were measured by alcohol wash and drop boards, and both gave similar estimates. Over the course of one season, the mean abundance of V. destructor increased from 0.002 to 0.11 mites per bee. Extended broodless periods during winter reduced the mean abundance of V. destructor by 28%, but mite mortality over winter was not high enough to prevent the need for treatment the following year. Apistan® was more effective than formic acid in both spring and fall treatments. Doses of one or two strips of Apistan® per colony were equally effective in spring or fall treatments. The mean abundance of V. destructor remained low throughout the season following spring treatment with either dose of Apistan®. Fall formic-acid treatments were more effective than spring treatments. Fluvalinate residues in samples of honey and wax collected from brood chambers and from honey supers were slightly higher in colonies treated with two strips of Apistan® than with one strip, but no detectible residue was found in extracted honey from 4500 commercial colonies treated in spring with Apistan® one strip per brood chamber for single or double storey hives. The levels of V. destructor in this study did not affect honey production or colony survival over winter.