Studies on the insect-resistance to insecticides : II. Resistance of human body louse, Pediculus humanus corporis de Geer, collected from different sources

Abstract

Studies of the development of DDT and γ-BHC (Lindane) resistance in natural populations of lice, Pediculus humanus corporis de Geer, in Japan have been conducted during 1952 and 1953. Lice were collected from five different localities in Japan for the comparison of their resistance to DDT and γ-BHC. They were Itabashi asylum in Tokyo where frequent dusting with 10% DDT powder had failed to control the lice and two slums and two primary schools (at Ueno in Tokyo, Sapporo, Ponbetsu, and Atsuda in Hokkaido) which, so far as could be learned, had been treated infrequently, if at all. They were continuously exposed on the filter paper in a petri dish treated with pp′-DDT (at the rate of 7g per square foot) and γ-BHC (at the rate of 0.234mg per square foot), and time-mortality were recorded. From these data the regression of probit mortality on log-time was computed, and the exposure time required to produce 50 per cent mortality (LT-50) in order to obtain the informations as to the relative resistance of the lice in the different installations. The LT-50 was 112.0 hours for the female and 71.26 hours for the male of the Itabashi strain, whereas 28.27 hours and 21.50 hours for the Sapporo strain, which indicated that the Itabashi strain could endure 3.31 to 3.96 times as much of DDT as that of the Sapporo strain. The lice from the slums at Ueno in Tokyo showed the LT-50 on DDT residues of 36.63 hours for the female and 25.48 hours for the male, while those of the lice from the Sapporo strain were 28.27 hours and 21.50 hours respectively. Three strains of Hokkaido were of similar LT-50. The DDT-resistant lice from the Itabashi colony showed no resistance at all to residues of γ-BHC, which gave nearly equal mortalities of the other three strains of lice except in the case of the Atsuda strain. The lice from the primary school at Atsuda showed somewhat less resistance to γ-BHC than those from any of the other sources, although these localities were not known to have been treated with γ-BHC. Genetical experiments of DDT-resistance with the Itabashi strain was also made. The F_1-adults from the crosses of Itabashi ♀×Ueno♂ and Ueno♀×Itabashi♂ were intermediate with regard to the DDT-resistance. Resistance inheritance factors are carried by both sexes.