Comparative Life Histories of Chlordane-Resistant and Nonresistant German Cockroaches12

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Abstract
The life histories of chlordane-resistant field-captured and chlordane-susceptible laboratory-reared Blatella germanica (I,,) were compared. German cockroaches highly resistant to chlordane, were collected en masse from Raleigh. N. C., dwellings (summer and winter) and transferred to a room maintained at 26.7°C and 55% relative humidity for comparison with a susceptible colony. There was no significant difference in the egg incubation period, 25-29 days. Nymphs emerged from egg cases while attached, and up to 15 days after detachment. Egg case mortality was highest among winter-collected females. Fewer nymphs emerged from egg cases of winter-collected females than from the susceptible females, and more nymphs emerged from egg cases of summer-collected, than from winter-collected females. No difference existed in the F1, generations. A fairly constant number of nymphs emerged per case for the first 3 egg cases of a female and decreased in succeeding cases. Development of nymphs from a given egg case to first adult and to all adults did not differ, with means of 59 and 99 days, respectively. Sex ratio approached 1:1. No correlations in time existed between the introduction of a virgin male to a virgin female and the first visible egg case, or between successive cases by a female. Fewer egg cases per female were produced by susceptible females than by females developing from summer-collected nymphs. Females maturing from resistant nymphs lived longer than their susceptible counterparts. Environmental conditions, such as food, water temperature, humidity, type of activity in infested buildings, and control procedures may be the cause of reported “change in habits and biology of resistant cockroaches,” rather than the change being due to the development of resistance.

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