Multiple Mechanisms of Pyrethroid Resistance in the German Cockroach, Blattella germanica (L.)

Abstract Pyrethroid-resistant German cockroaches known as the Village Green strain were compared to a susceptible (Orlando Normal) strain in respect to possible mechanisms of insecticide resistance. Male adults of the resistant strain weighed 15% more than susceptible roaches of the same cumulative age from adult eclosion. Based on the topical application of different concentrations of permethrin, the KD 50 for resistant roaches was 20-times greater than that for susceptible insects. Reduced penetration of [ 14 C]permethrin was observed in resistant insects during 24 hr after treatment along with increased in vivo metabolism as compared with susceptible controls. The cytochrome P450 content and monooxygenase activity when measured with methoxyresorufin and benzo[ a ]pyrene was elevated in resistant roaches by as much as 6.9-fold but no difference was found with benzphetamine. The glutathione transferase activity was also increased (1.6-fold with chlorodinitrobenzene) and elevated esterase activity was detected with the substrates, 1-naphthyl acetate (1.7-fold) and p -nitrophenyl acetate (2.1-fold). Using isoelectric focusing, a novel E 2 esterase was identified in resistant cockroaches not found in the susceptible population. E 2 may be partly responsible for the increased esterase activity observed in resistant roaches. Increased esterase activity toward p -nitrophenyl acetate was used to develop a kinetic, diagnostic assay that could rapidly discriminate resistant from susceptible individuals.