Response of the German Cockroach to Sublethal Concentrations of DDT and Benzene Hexachloride1

Abstract

Strains of the cockroach were reared in the laboratory through 7 generations of selection for survival to treatments with DDT and benzene hexachloride. The criterion of selection after the 1st generation was survival to treatments which gave 75% or higher kill. The procedure employed in making the treatments is described. In the 7th generation, 23 and 4.0 times as much DDT were required to kill 50 and 95%, respectively, of the DDT-strain males as untreated-strain males. Similarly, 14.3 and 7.8 times as much DDT were required to obtain 50 and 95% mortalities of the DDT-strain females as untreated-strain females. The male and female roaches in the benzene hexachloride strain were only slightly more resistant in the 7th generation to benzene hexachloride than those of the untreated strain. No significant difference in reproductive performance between treated and untreated strains was found. However, the avg. number of nymphs per female and nymphs per egg case produced within the DDT strain were rather consistently lower than in the other 2 strains. The width and length of empty egg cases produced in the 7th generation by DDT-strain females, and the length of those produced by benzene hexachloride-strain females, were significantly less than similar measurements made on empty egg cases produced by females within the untreated strain.