Insecticide resistance and synergism in field collected German cockroaches (Dictyoptera: Blattellidae) in Peninsular Malaysia

Twelve strains of German cockroach, Blattella germanica (Linnaeus) were collected from various locations in Peninsular Malaysia and tested for their susceptibility to three groups of insecticides applied topically. The levels of resistance were low to high (2.8 to 92×) for carbamates (propoxur and bendiocarb), low (2.0 to 7.6×) for organophosphate (chlorpyrifos) and low to moderate (1.0 to 23×) for pyrethroids (cypermethrin and permethrin) when compared to a susceptible strain. Five strains, resistant to both cypermethrin and permethrin, were also resistant to DDT, phenothrin and deltamethrin. Propoxur resistance in ten strains was suppressed with the synergists, piperonyl butoxide (PBO) and S,S,S-tributylphosphorotrithioate (DEF), suggesting monooxygenase and esterase involvement in the resistance. However, the levels of resistance for cypermethrin and permethrin were not affected when using either PBO or DEF.