Mechanisms of pyrethroid resistance in the German cockroach, Blattella germanica (L.)

A pyrethroid resistant German cockroach strain, Apyr-R, was collected from Opelika, Alabama, after control failures with permethrin and deltamethrin. Levels of resistance to permethrin and deltamethrin in Apyr-R were 97- and 480-fold, respectively, compared to an insecticide susceptible German cockroach strain ACY. When cockroaches were pre-treated with piperonyl butoxide (PBO), an inhibitor of cytochrome P450 monooxygenases, resistance levels to permethrin and deltamethrin were reduced to 17- and 70-fold, respectively, suggesting that P450 monooxygenases were involved in the resistance. Similarly, when cockroaches were pre-treated with S,S,S-tributylphosphorotrithioate (DEF), an inhibitor of hydrolases, resistance levels to permethrin and deltamethrin were reduced to 22- and 81-fold, respectively, indicating that hydrolases are also involved in the resistance. Injection of permethrin and deltamethrin did not change the level of resistance to either compound, suggesting that decreased cuticular penetration may not play an important role in pyrethroid resistance in the Apyr-R strain.;In order to understand whether target site insensitivity resulting from a Leu to Phe mutation in para-homologous sodium channel was involved in the resistance of Apyr-R, para-homologous sodium channel gene fragments were generated by reverse transcription mediated polymerase chain reaction (RT-PCR) from both Apyr-R and ACY. Sequencing results revealed that the Leu to Phe mutation in the sodium channel gene was present in the Apyr-R strain, suggesting that target site insensitivity might be involved in the resistance. Two overexpressed genes in Apyr-R compared to ACY were identified by subtractive hybridization and cDNA array techniques. One of the two overexpressed genes had 55% homology with Drosophila melanogaster cytochrome P450 4G15 and was named CYP4G19, and the other shared 98.8% identity with the amino acid sequence of Blattella germanica cytochrome c oxidase subunit I (COXI) protein. The overexpression of CYP4G19 and COXI was developmentally regulated in Apyr-R, with CYP4G19 overexpressed in both nymph and adult stages while COXI only overexpressed in the adult stage. The overexpression of CYP4G19 might be responsible for PBO suppressible resistance in Apyr-R. The overexpression of COXI might be an additional mechanism involved in the resistance. This is the first attempt to identify genes associated with pyrethroid resistance within the context of the German cockroach genome without any preconceptions of their nature. This research provides important information for the understanding of pyrethroid resistance mechanisms in the German cockroach, Blattella germancia (L.).