Abstract: The induction of the cytochrome P450 (cyt-P450) by 2-tridecanone in cotton bollworm, Helicoverpa armigera (Hübner) larvae was investigated. By mixing 2tridecanone at low dosages (0.005%～0.01%) for three generations, the content and difference spectra of cyt-P450 interacted with CO and ligands, including pyridine，n-butanol，aniline and cyclohexane, were investigated with cyt-P450 preparation from midgut and fat body of the sixth instar cotton bollworm. The maximal absorption of cyt-P450 interacted with CO was observed around 449 nm for midgut preparation and 450.70 nm for fat body preparation respectively based on 15 to 40 scans in the induction colony, and 449.22 nm for midgut preparation and 449.20 nm for fat body preparation respectively in the control colony. Besides an absorption peak around 449 nm, there were in turn three other absorption peaks around 414, 415, 419 nm in midgut cytochrome P450, thereafter the absorption disappeared, and there was a weak absorption at 420 nm at the thirty-first scan. In the absorption spectrum of cyt-P450 bound with n-butanol, two peaks and two troughs occurred for midgut preparation and one peak and one trough in fat body preparation. The maximal absorption peaks were at 380.10 nm, 415.02 nm for midgut preparation and 416.61 nm for fat body preparation, while the absorption troughs were at 395.02 nm, 423.24 nm for midgut preparation and 424.91 nm for fat body preparation. Characteristic type Ⅱ spectrum occurred with cyt-P450 bound with pyridine, for midgut preparation with a maximal absorption at 425.57 nm and a trough at 395.48 nm; for fat body preparation with a maximal absorption at 422.19 nm and a trough at 415.90 nm. Uncharacteristic type Ⅰ spectrum occurred with cyt-P450 bound with cyclohexane, for midgut preparation with maximal absorption peaks at 378.00 nm and 448.12 nm; for fat body preparation with the maximal absorption peaks at 380.00 nm and 434.04 nm. Type Ⅱ spectrum occurred with cyt-P450 bound with aniline, for midgut preparation with a maximal absorption at 443.30 nm and a trough at 402.30 nm; for fat body preparation with a maximal absorption at 428.92 nm and a trough at 401.00 nm.

Key words: Helicoverpa armigera, cytochrome P450, 2tridecanone, induction, difference spectra