Second survey of insecticid-resistance in body-lice, 1958-63.

Between 1953 and 1956 the World Health Organization carried out a global survey of the susceptibility of body-lice to insecticides. A second survey was organized in 1958; this paper summarizes the results of susceptibility tests done in 22 countries over the period 1958-63.Resistance to DDT has been found in a number of countries. The LC(100) for resistant body-lice has been found to be over 5% DDT, the LC(100) for hybrids to be between 1% and 5% DDT; and the LC(50) for susceptible genotypes has been estimated to be less than 0.04% DDT.Body-lice continue to be susceptible to gamma-HCH and pyrethrins in most countries, although they show increased tolerance to gamma-HCH in Egypt. Their susceptibility to malathion in various localities in Egypt has been assessed, and the LC(50) found to range from 0.02% to 0.032%.