Block Residual Spraying of Premises with DDT for the Control of Malaria

Abstract

Summary 1. All structures of 299 premises in a block of over 38 square miles in Wheeler Reservoir, North Alabama, were sprayed in June with approximately 200 mgm. of DDT per sq. ft., and a similar block was maintained as a control. Inspections of more than one-fourth of all premises in the two areas were made three times each month during July, August, and September and densities of A. quadrimaculatus recorded. The single application of spray markedly reduced the number of mosquitoes for a period in excess of three months. It appears from our observation that residual spraying of premises provides a more effective barrier to the transmission of malaria than does house spraying alone. 2. The study did not elicit any significant decline in mosquito density in the treated area as indicated by larval density, counts from keg shelters or the untreated surfaces of barns. 3. The added cost in this study of spraying all structures on premises was not in excess of one-third the cost of spraying the houses alone—$3.92 compared to $3.00. 4. The importance of treatment of large blocks of premises is emphasized. 5. On the basis of previous information on human blood feeding of A. quadrimaculatus and the present observation of almost complete elimination of this species within the premise by DDT residual spraying of all structures, it appears that complete DDT residual spraying offers more protection against malaria transmission than mosquito-proofing with its practical limitations. 6. Many beneficial side effects as regards a public health program result from the residual spray application including the control of other disease transmitting and pest insects.