Induction of the cytochrome P450 activity by plant allelochemicals in the cotton bollworm, Helicoverpa armigera (Hübner)

The p-nitroanisole O-demethylase activity of P450s and expression of CYP6B6 mRNA induced by two plant secondary substances, 2-tridecanone and quercetin, were investigated in cotton bollworm, Helicoverpa armigera (Hübner). The O-demethylase activity was higher in the fat body than that in the midgut of the sixth-instar larvae fed on the artificial diets mixed with these allelochemicals. The similar results were obtained when induced by the combination of 2-tridecanone and quercetin at different concentrations. When the concentration of inducers, mixture of 2-tridecanone and quercetin, was 0.5 mg/ml in the diet, the maximum O-demethylase activities of P450 in the midgut and fat body were 2.6 and 3.88 times higher than those in the relevant control, respectively. Specific primers were designed according to the CYP6B6 and an actin gene of cotton bollworm and used to determine the expression level of CYP6B6 mRNA in the midgut and fat body by a reverse transcription-polymerase chain reaction (RT-PCR) method. The expression levels of CYP6B6 mRNA were obviously correlated with the concentrations of 2-tridecanone, but no correlation with the concentrations of quercetin. When induced with the mixture of 2-tridecanone and quercetin at a concentration of 0.5 mg/ml in the diet, the maximum expression amount of CYP6B6 mRNA in the midgut and fat body was induced, which was 1.74 and 1.8 times compared with the corresponding control, respectively. It suggests that the cytochrome P450 has an important role in the metabolism of plant secondary substances in cotton bollworm.