Cross Resistance to Organophosphorus Compounds in Malathion- and Diazinon-Resistant Strains of Blattella germanica1

Dosage mortality data, obtained by a topical application method, for 8 organophosphorus compounds are given for 2 laboratory-selected strains of Blattella germanica (L.), one selected with malathion and the other with diazinon. Comparison of these data with similar data for a normal susceptible strain revealed that development of resistance to malathion in this species is highly specific, imparting essentially no cross resistance to any of the other 7 organophosphorus compounds evaluated. Selection with diazinon induced a low level of tolerance to all the organophosphates studied. There is reason to believe that if carboxyesterase activity is responsible for the resistance phenomena to malathion exhibited by this insect, its action is blocked by the presence of a vinyl group in one of the carboxyester side chains of an organophosphorus compound, such as GC 3707 (dimethyl 3- (dimethoxyphosphinyloxy) glutaconate).