Pyrethroid resistance and cross-resistance in the German cockroach, Blattella germanica (L)

German cockroach (Blatella germanica (L)) strain, Apyr-R, was collected fro m Opelika, Alabama after control failures with pyrethroid insecticides. Lev els of resistance to permethrin and deltamethrin in Apyr-R (97- and 480-fol d, respectively, compared with a susceptible strain, ACY) were partially or mostly suppressed by piperonyl butoxide (PBO) and S,S,S,-tributylphosphoro trithioate (DEF), suggesting that P450 monooxygenases and hydrolases are in volved in resistance to these two pyrethroids in Apyr-R. However, incomplet e suppression of pyrethroid resistance with PBO and DEF implies that one or more additional mechanisms are involved in resistance. Injection, compared with topical application, resulted in 43- and 48-fold increases in toxicit y of permethrin in ACY and Apyr-R, respectively. Similarly, injection incre ased the toxicity of deltamethrin 27-fold in ACY and 28-fold in Apyr-R. The se data indicate that cuticular penetration is one of the obstacles for the effectiveness of pyrethroids against German cockroaches. However, injectio n did not change the levels of resistance to either permethrin or deltameth rin, suggesting that a decrease in the rate of cuticular penetration may no t play an important role in pyrethroid resistance in Apyr-R. Apyr-R showed cross-resistance to imidacloprid, with a resistance ratio of 10. PBO treatm ent resulted in no significant change in the toxicity of imidacloprid, impl ying that P450 monooxygenase-mediated detoxication is not the mechanism res ponsible for cross-resistance. Apyr-R showed no cross-resistance to spinosa d, although spinosad had relatively low toxicity to German cockroaches comp ared with other insecticides tested in this study. This result further conf irmed that the mode of action of spinosad to insects is unique. Fipronil, a relatively new insecticide, was highly toxic to German cockroaches, and th e multiresistance mechanisms in Apyr-R did not confer significant cross-res istance to this compound. Thus, we propose that fipronil could be a valuabl e tool in integrated resistance management of German cockroaches. (C) 2001 Society of Chemical Industry.