House spraying. DDT is effective and cheaper than the pyrethroids. I kg of DDT costs 6 US $ whereas the same amount of pyrethroid costs on average 90 US $. 1kg DDT gives 12 litres of water and insecticide; 1 kg of pyrethroids gives 80 litres. The cost per litre is therefore 50 cents for DDT and $1.13 US for the pyrethroids. Ironically in Zambia, resistance to DDT has not been described(Anopheles gambiae and A. funestus being the main vectors), whereas resistance to pyrethroids has been described in a nearby area. DDT persists longer on the treated surfaces than the pyrethroids. It remains effective for 1-2 years compared to the pyrethroids, which are effective for 9-11 months. Porous walls are common, and DDT being poorly absorbed, unlike the pyrethroids, is therefore ideal.

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