A strain of German cockroach, Blattella germanica (L.), collected from an institutional kitchen and cafeteria in Marietta, GA, in 1992, was examined for insecticide resistance. Topical insecticide bioassays revealed that the Marietta strain was resistant to bendiocarb (46-fold), cypermethrin (28-fold), propoxur (17-fold), permethrin (12-fold), and chlorpyrifos (7-fold). Pretreatment with the cytochrome P450 monooxygenase inhibitor, piperonyl butoxide, reduced the resistance level to the carbamates to varying degrees, but resulted in an increased resistance ratio to the pyrethroids. Similarly, the esterase inhibitor, S,S,S-tributyl phosphorotrithioate (DEF), partially reduced the resistance to bendiocarb while increasing the resistance ratio to permethrin. Detoxication enzyme assays revealed that activities of microsomal oxidases (aldrin epoxidase, phorate sulfoxidase, methoxyresorufin O-demethylase, p-chloro-N-methylaniline N-demethylase, ethoxycoumarin O-deethylase), glutathione S-transferases (DCNB, CDNB, PNPA), hydrolases (general and carboxylesterase), and cytochrome c reductase were 1.4- to 18-fold higher in the Marietta strain than in the susceptible strain. In addition, levels of cytochrome P450 and cytochrome b(5) were 2.5- and 2.3-fold higher in the resistant strain than in the susceptible strain. The bimolecular rate constant for the inhibition of acetylcholinesterase by dichlorvos was similar in the resistant and susceptible strains. The results indicated that the broad spectrum of insecticide resistance observed in the Marietta strain was the result of multiple resistance mechanisms.
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