The Use of residual Films of DDT and Gammexane in Malaria Control

Abstract

(1) Sprays that are atomised and mingled with air were unsuitable because they were wasteful in both material and labour.(2) Knapsack oilers and modified stirrup pumps were efficient. Where labour is cheap hand-operated sprayers of this type are more economical than motoroperated machines.(3) The relation between mosquito mortality and infectivity is discussed and it is calculated that any treatment which produces 75 per cent. mortality among the mosquitos exposed to it should effect malaria elimination.(4) The effects of a DDT emulsion were much more durable than those of a similar quantity of DDT in kerosene solution. The difference was much less marked when Gammexane was used. Emulsions will probably displace kerosene solutions as vehicles for the application of residual films.(5) The persistence of the effects of DDT was markedly increased by increased dosage, so that it will be most economical to apply DDT in heavy doses at long intervals.(6) The persistence of Gammexane effects was not greatly increased by increased dosage because it evaporates much more quickly than DDT. It is not likely to be effective for much longer than 10 weeks.(7) Treatments with DDT were usually effective against A. minimus for about twice as long as against A. vagus or Culicines, but treatments with Gammexane had similar effects on all species.