Level of Pyrethroid-resistance Associated with Cytochrome P450 Expression in German Cockroach Blattella germanica (Blattodea: Ectobiidae) in the Field Collected Strains

Cytochrome P450-dependent monooxygenases are a very important metabolic system involve in insecti cide resistance. This study was conducted to find the association between the expression level of cytochrome P450 (CYP450) and permethrin-resistance level among four strains of the German cockroach Blattella germanica (L) (Blat todea: Ectobiidae).

Three field strains of German cockroach with different frequency of exposure to pesticides, and a laboratory susceptible strain were used in the present study. Insecticide susceptibility bioassays were carried out to detect re sistance to permethrin. The concentration of CYP450 in each strain was determined using ion-exchange HPLC chroma tography. Biochemical assays was performed to analyse CYP450 activities.

The resistance ratios (RR) to permethrin among three field strains were 3.29, 4.10 and 6.17-fold comping with the susceptible stain. The CYP450 activity of three field strains was 1.6, 2.4 and 2.7 times higher than in the sus ceptible stain. The amount of CYP450 per mg of protein was significantly different between the susceptible and the three re sistant strains. The resistant cockroaches showed a relatively high expression of CYP450 enzymes. A strong corre la tion was found between permethrin resistance level and total concentration of CYP450 enzymes.

The results of current study show that more frequent usage of a pyrethroid insecticide cause the metabolic insecticide resistance to rise in German cockroach. Therefore, there is a ratio correlation between resistance level and monooxygenases activities in insect. Thus, the control program must be managed according to history of pesticide us age.