Contact toxicity of permethrin-impregnated military uniforms to Culex pipiens (Diptera:Culicidae) and Phlebotomus papatasi (Diptera: Psychodidae): effects of laundering and time of exposure.

The effects of laundering and time of exposure on the insecticidal activity of military uniform fabric impregnated with permethrin at 0.125 mg active ingredient (AI)/cm2 are reported from susceptibility tests with laboratory-reared mosquitoes, Culex pipiens, and sand flies, Phlebotomus papatasi. Knockdown/mortality resulting from exposure of groups of female insects for periods of 1, 3, 5, 7, and 10 min was recorded and compared among 5 different treatment/wash groups (untreated/unwashed, treated/unwashed, treated/1-wash, treated/2-wash, treated/3-wash). Laundering was by machine washing with detergent and warm water followed by hot-air machine drying. Post-exposure assessments at intervals from 0 to 60 min and at 24 h showed that knockdown for each exposure time and wash group was initially low but increased steadily during the first hour post-exposure. Sand flies were less sensitive than mosquitoes to knockdown during the first 60 min after contact with treated/unwashed fabric; however, 24-h mortality rates for sand flies were higher as compared with mosquitoes. The permethrin remaining after a 3rd wash had little knockdown effect on mosquitoes but was toxic to sand flies at each of the 5 exposure times. Significant reductions in the knockdown effectiveness of permethrin-treated fabric to mosquitoes and sand flies was associated with single and repeated washings of the fabric.