Abstract: Treatment in vivo with PBO caused apparent reduction of the cytochrome P450 level in third instar larva of Helicoverpa armigera. At 1 hour after PBO treatment, the content of cytochrome P450 was only 43.9% of that in the control. At 12 hours after PBO treatment, the content of cytochrome P450 decreased to 23.4% of the control. While 18 and 24 hours after treatment, the content of cytochrome P450 was 85.8% and 70.0% of the control respectively. The bioassay results indicated that PBO synergised 7 pyrethroids significantly, with the highest synergistic ratio (119.3) for fenvalerate and the lowest (2.1) for permethrin. Because the cytochrome P450 is an important detoxifying enzyme, the reduction of the cytochrome P450 level can impede the oxidative metabolism and cause obvious synergism to pyrethroids in H.armigera.

Key words: Helicoverpa armigera (Hübner), cytochrome P450, piperonyl butoxide, insecticide resistance