Further Selection of Normal and Chlordane-Resistant German Cockroaches for Resistance to Malathion and Diazinon1

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Abstract
Continued laboratory selection studies of malathion- and diazinon-resistant cockroaches (Blattella germanica (L.)) are reported. The nymphs were exposed to residual deposits of these materials on tempered Masonite and glass surfaces. The criterion of selection was > 80% kill. Dosage-mortality data were periodically obtained for males and females from the selected strains, but complete data on only the females are presented. The following levels of resistance were obtained at LC-50 and LC-90, respectively, in the normal strain selected with malathion: 13.3X and 24.8X in the F9 generation, and 115.6X and 53.9X in the F15 generation. Similarly, in the chlordane-resistant strain selected with malathion the values were: 48.0X and 38.6X in the F10 generation, and 133.4X and 55.3X in the F16 generation. No significant resistance to diazinon was indicated after 15 or 16 generations of selection.