Some Biological Comparisons of Resistant and Nonresistant Strains of the German Cockroach, Blattella germanica1

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Abstract
Strains of the German cockroach (Blattella germanica (L.)) resistant to lindane, chlordane, and DDT were compared with a normal strain as to incubation period of eggs, developmental period of nymphs, and longevity of adults. In most comparisons, the resistant strains were more heterogeneous than the normal strain. The average incubation period in the DDT-resistant strain was shorter than in any of the other three strains, none of which were different from each otner. The nymphal developmental periods for males and females in either the DDT- or lindane-resistant strains were longer than the corresponding ones in either the chlordane-resistant or normal strains. The females in all of the resistant strains lived longer on the average than normal females, but there was no significant difference in longevity of males between any of the strains. All differences reported were highly significant. Data are presented on mortality of gravid females, percentage of nonhatching egg cases, and sex ratios in the different strains. Some possible relationships between development of resistance and certain biological changes are briefly discussed.