| Abstract: | Between December 1947 and May 1949, six colonies of Pediculus humanus humanus L. (P. h. corporis Deg.) from various sources were cultured in England in the laboratory on the human leg. Three of the strains originated from natural infestations in England, and the others came from laboratory cultures in Hamburg, Basle and Tunis. After the strains had been bred for at least one generation in the laboratory, lice from each were exposed to standard DDT-impreseated fabrics to test their resistance, if any. Only the strain from Tunis showed evidence of abnormal resistance. This strain had been maintained in the laboratory there for about 12 years, and in tests with three successive generations, its resistance varied significantly from one generation to the next.
Colonies of Acdes aegypti (L.) from Karachi, Poona and Delhi, which were being maintained at a laboratory in Lagos, were compared with a local Nigerian strain for resistance to DDT by Busvine in 1952. Extensive tests in which the mosquitos were exposed for one hour in filter-paper cylinders impregnated with oil solution of DDT [cf. E.A.E., B 41 156] showed no difference in the average susceptibility of the four strains, though there was a significant difference between the Karachi and Nigerian strains in the extent of variation in susceptibility. Comparative tests also showed no difference in susceptibility to y BHC between a laboratory culture of A. aegypti at Lagos and a colony started with larvae from Ilaro, a Nigerian town in which all the houses had been sprayed with BHC (10-15 mg. γ isomer per sq. ft.) every three months for 21/2 years.
In 1952, Busvine also compared the susceptibility to insecticides of four strains of house-flies of which colonies were maintained at Lagos on monkey faeces as oviposition medium and larval food. They comprised a normally susceptible strain of Musca domestica domestica L. from England, strains of M. d. vicina Macq. and M. sorbens Wied. from Yaba, near Lagos, and a strain of M. d. vicina from Ilaro. The flies were treated individually with drops of oil solution of insecticide applied dorsally. On the basis of median lethal concentrations, Yaba vicina was somewhat more susceptible to y BHC and dieldrin and sorbens was considerably more susceptible to y BHC and DDT than was domestica from England. These differences could be explained by the smaller average sizes of the two susceptible strains. On the other hand, each of the vicina strains was 5-4 times as resistant to DDT as English domestica, although no DDT had been used at liaro and little, if any, in Lagos. Ilaro vicina was 11.4 times as resistant to y BHC and nearly twice as resistant to dieldrin as Yaba vicina and 5.7 times as resistant to y BHC as domestica from England.
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