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

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Abstract
German cockroaches (Blattella germanica (L.)) from chlordane- resistant and normal strains were each placed under selection pressure to malathion and Diazinon®(O, O-diethyl O-2-isopropy1-4-methyl-6-pyrimidinyl) phosphorothioate) in the laboratory by exposing the nymphs to residual deposits of these materials on tempered Masonite and glass surfaces. The criterion of selection was >50% kill in the parental, Fl and F2 generations; >65% kill in the next two or three generations; and > 80% kill thereafter. Male and female cockroaches from all four selected strains were periodically tested for development of resistance, but data are presented herein for only the females. The following orders of resistance were obtained at LC-50 and LC-90, respectively: 6.9 × and 1.5 × in the normal strain selected to malathion when tested on filter paper, and 13.1 × and 17.8 × in the same strain when tested on panels; 9.4 × and 1.4 × in the chlordane-resistant strain selected to malathion when tested on filter paper, and 42.9 × and 24.3 × when tested on panels. Males and females in the chlordane-resistant strain were originally more susceptible to malathion than those in the normal strain, but development of resistance occurred more rapidly in the former, especially in the males, when it was placed under selection pressure to malathion. Slight shifts toward steeper regression lines for Diazinon-selected strains occurred after six or seven generations, but the selected strains exhibited no detectable resistance to Diazinon.