Resistance to Three Organophosphorus Insecticides in Strains of the German Cockroach from Texas

In 1963 some pest-control operators in Texas experienced failures in controlling German cockroaches, Blattella germanica</it> (L.), with insecticides that had previously given satisfactory control. Five strains from 3 locations were tested in the laboratory and compared with a normal strain for determination of level of resistance. At LC<inf>50</inf> the times resistances were: to diazinon 2.5–6.3; to fenthion 2.7–5.0; and to malathion 2.2–12.8. At LC<inf>90</inf> the values were: to diazinon 2.9–8.2; to fenthion 3.2–9.9; and to malathion 1.9–26.7.