τ-Fluvalinate is a pyrethroid acaricide.1It induces tail currents in Western honeybee (A. mellifera) voltage-gated sodium channels (AmNav1) expressed inXenopusoocytes (EC50= 60 nM). It also induces tail currents in honeybee parasitic Varroa mite (V. destructor) Nav1 channels (VdNav1) expressed inXenopusoocytes (EC50= 160 nM) with a faster tail current decay than that of AmNav1 channels. Topical application of τ-fluvalinate (2 μl) in combination with coumaphos , atrazine , 2,4-DMPF, chlorpyrifos , and chlorothalonil does not affect honeybee queen mass, egg-laying patterns, or the mass of daughter worker bees at emergence.2Formulations containing τ-fluvalinate have been used to control Varroa mites in beehives.