Abstract: Phenobarbital (2 mg/g) and fenvalerate (0.2 mg/g) mixed in diets caused significant induction of cytochrome P450 and cytochrome c reductase in midgut of susceptible strain of the cotton bollworm, Helicoverpa armigera. The Induction ratios of phenobarbital and fenvalerate were all 2.24-fold to cytochrome P450, 1.33- and 1.40-fold to cytochrome c reductase, and 1.23- and 1.15-fold to cytochrome b5, respectively.Moreover, phenobarbital showed significant induction to activity of aldrin-epoxidase and ethoxyresorufin-demethylase in midgut of the strain, which was 2.75- and 2.66-fold respectively, but no induction to 7-ethoxycoumarin-deathylase activity (0.88-fold); fenvalerate showed 2.02-fold Induction to aldrin-epoxidase activity in the same tissue. To the resistant strain, phenobarbital and fenvalerate induced only cytochrome c reductase in midgut to significant level, which was 1.48-and 1.86-fold respectively. The induction ratios of phenobarbital and fenvalerate to cytochrome P450 in midgut of resistant strain were 1.21-and 1.15-fold respectively, while to cytochrome b5 only 1.15-and 0.98-fold respectively. In addition, fenvalerate caused 1.53-fold Induction of aldrin-epoxidase activity in midgut of resistant strain, while phenobarbital caused significant inhibition to it.

Key words: Helicoverpa armigera, mixed_function oxidases, fe nvalerate, phenobarbital, induction, cytochrome P450