Induction of cytochrome P450CYP6B7 and cytochrome b(5) mRNAs from Helicoverpa armigera (Hubner) by pyrethroid insecticides in organ culture

An organ culture system derived from Helicoverpa armigera has been used to study the expression of cytochrome P450 and cytochrome b5 mRNAs, Northern a nalysis showed that levels ol: the mRNAs for cytochrome P450s, CYP6B2, CYP6 B6 and CYP6B7, and cytochrome b5 in control tissue were commensurate with t hose in the tissue of whole larvae. Substantial induction of cytochrome P45 0, CYP6B7 and cytochrome b5 mRNAs by oc-pinene, and the pyrethroids, fenval erate, cypermethrin and permethrin were observed in fat body culture. Neith er mRNA was induced, either in midgut or integument organ cultures. In cont rast, the relatively water-soluble compound phenobarbital, could induce CYP 6B7 mRNA but not cytochrome b5 mRNA in fat body cultures. As for pyrethroid s, phenobarbital had no effect on the other tissues in culture, These resul ts confirm a previous conclusion that pyrethroids could induce CYP6B7 mRNA, which was based upon a very slight induction observed in living insects, B ecause many cytochrome P450 substrates can act as their inducers, these res ults support a previous conclusion that CYP6B7 could be the enzyme that is involved in pyrethroid resistance in H. armigera.