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The synthetic pyrethroid, permethrin, when applied to clothing with a pressurized spray at an application rate estimated previously to be 4 micrograms a.i./cm2, was found to be 100% effective for personal protection against all three parasitic stages of the western black-legged tick, Ixodes pacificus Cooley and Kohls. This tick has been implicated as the primary vector of the
Lyme disease spirochete (Borrelia burgdorferi) to humans in the far-western United States. Periods of exposure to permethrin-treated cloth as brief as 10 and 45 seconds incapacitated 100% of subadult and adult ticks, respectively, within 1-3 h post-treatment. Under field conditions, permethrin apparently does not repel questing adult ticks, though 100% of ticks recovered from treated clothing after exposures as brief as less than or equal to 15 seconds were moribund 1 h later.