Comparison of different insecticides and fabrics for anti-mosquito bednets and curtains

Various formulations of six insecticides (a carbamate and five pyrethroids), were impregnated into bednets and curtains made from cotton, polyester, polyethylene or polypropylene fabric. For bioassays of insecticidal efficacy, female Anopheles gambiae mosquitoes were made to walk on the fabrics for 3 min and mortality was scored after 24 h. The main concentrations tested were: bendiocarb 400 mg/m2, cyfluthrin 30-50 mg/m2, deltamethrin 15-25 mg/m2, etofenprox 200 mg/m2, lambda-cyhalothrin 5-15 mg/m2 and permethrin 200-500 mg/m2. Field trials in Tanzania used experimental huts (fitted with verandah traps) entered by wild free-flying Anopheles gambiae, An.funestus and Culex quinquefasciatus mosquitoes. Results of testing the impregnated fabrics in experimental huts showed better personal protection provided by bednets than by curtains. Permethrin cis:trans isomer ratios 25:75 and 40:60 were equally effective, and the permethrin rate of 200 mg/m2 performed as well as 500 mg/m2. Bioassay data emphasized the prolonged insecticidal efficacy of lambda-cyhalothrin deposits, except on polyethylene netting. Most of the impregnated nets (including the 'Olyset' net with permethrin incorporated during manufacture of the polyethylene fibre) and an untreated intact net performed well in preventing both Anopheles and Culex mosquitoes from feeding on people using them overnight in the experimental huts. Anopheles showed high mortality rates in response to pyrethroid-treated nets, but only bendiocarb treated curtains killed many Culex. Holed nets treated with either cyfluthrin (5 EW formulation applied at the rate of 50 mg a.i./m2) or lambda-cyhalothrin (2.5 CS formulation at 10 mg a.i./m2) performed well after 15 months of domestic use. Treatment with deltamethrin SC or lambda-cyhalothrin CS at the very low rate of 3 mg/m2 gave good results, including after washing and re-treatment.