Laboratory evaluation of efficacy of bednets impregnated with pyrethroids.

The half-life of an insecticide on a treated object can be used as a crucial test for evaluating the residual effect. On cotton and nylon bednets, the half-life of deltamethrin was 65.6 and 55.4 days, whereas the half-life of permethrin on cotton and nylon bednets was 35.0 and 27.4 days. A deltamethrin-impregnated bednet (10 mg/m2) is effective for 6-7 months and costs less than DDT residual spraying (2g/m2) on the inner walls of rooms.