Variability of resistance mechanisms in pyrethroid resistant German cockroaches (Dictyoptera: Blattellidae)

Mechanisms of pyrethroid resistance were compared in German cockroach strains, Apyr-R, Bpyr-R, and Cpyr-R, collected from Opelika, Alabama, after control failures with pyrethroid insecticides. Resistance to permethrin in Bpyr-R (54-fold, compared with a susceptible strain, ACY) and Cpyr-R (46-fold) was slightly suppressed by piperonyl butoxide (PBO) and S,S,S,-tributylphosphorotrithioate (DEF). Given that DEF is not a completely specific inhibitor of hydrolases and that it can inhibit microsomal oxidases at high concentration, these data should be interpreted with caution. These results suggest that P450 monooxygenases and, perhaps, hydrolases play minor roles in permethrin resistance in both strains. However, resistance to deltamethrin in both Bpyr-R (50-fold) and Cpyr-R (47-fold) was not decreased by PBO or DEF. These results were different from that in Apyr-R where levels of resistance to permethrin and deltamethrin were dramatically decreased by PBO and DEF. It is likely that these German cockroach strains from the same geographic origin exhibit diverse mechanisms of pyrethroid resistance. Injection did not decrease levels of resistance to either permethrin or deltamethrin in Bpyr-R and Cpyr-R, which is similar as the result in Apyr-R, suggesting that a decreased rate of cuticular penetration does not play an important role in pyrethroid resistance in these strains. A 408 bp para-homologous sodium channel gene fragment where the para (kdr) mutation resides was generated by RT-PCR from German cockroach strains. We found that the para mutation was present in Apyr-R, but not in ACY, Bpyr-R, and Cpyr-R, suggesting that the para mutation is one of the important factors in pyrethroid resistance in Apyr-R but not an important contributing factor to pyrethroid resistance in Bpyr-R and Cpyr-R. Interestingly, a new mutation, T to C at nt 2996 resulting in a phenylalanine(999) to serine(999) amino acid change, was detected in both Bpyr-R and Cpyr-R. The importance of this mutation in resistance is discussed. (C) 2002 Elsevier Science (USA). All rights reserved.