Seven insecticides, fenitrothion, d-phenothrin, fenvalerate, permethrin, cyphenothrin and fenpropathrin, were each impregnated onto wide-mesh netting and bioassayed for insecticidal activity against Culex mosquitoes. After 9 months of aging, cyphenothrin was the most effective chemical. The movement of adult females through untreated nets was recorded. When the size of the opening of the mesh was less than the width of wing expanse, the mosquitoes were found to rest on the netting before they passed through, thus allowing them time to pick up a lethal dose of the insecticide.