Cytochrome P450CYP6X1 cDNAs and mRNA expression levels in three strains of the tarnished plant bug Lygus lineolaris (Heteroptera: Miridae) having different susceptibilities to pyrethroid insecticide

Three cDNAs, cloned from both pyrethroid-susceptible and -resistant strains of Lygus lineolaris , contained a 1548 nucleotide open reading frame encoding a 516 amino acid residue protein. Predicted cytochrome P450s from cDNAs were classified as the first three new members of subfamily CYP6X, CYP6X1v1 for a susceptible strain and CYP6X1v2 and CYP6X1v3 for two resistant strains. Putative cytochrome P450 CYP6X1s from L. lineolaris were highly similar (up to 42% amino acid sequence identity) to several insect CYP6s that are responsible for reduced sensitivity to pyrethroid insecticides. A total of twenty-six nucleotide substitutions were revealed between cDNAs of susceptible and resistant strains. Two nucleotide substitutions resulted in amino acid changes, Asp(373) to Ala(373) and Ser(487) to Ala(487) , between susceptible and resistant strains. The resistant laboratory strain contained 2.1-fold higher cytochrome P450 mRNA per microgram total RNA than the susceptible laboratory strain. Topical treatment with 10 ng permethrin elevated cytochrome P450 mRNA levels by approximately 2-fold. The results of this study indicated that cytochrome P450 gene mutation, coupled with up-regulation, was present only in the pyrethroid resistant strains, and was possibly related to resistance development in the tarnished plant bug.