Resistance Risk Assessment To Metaflumizone And P450 CYP6CV2 Gene Induced Expression In Plutella Xylostella

Plutella xylostella (L.), English name of Diamondback moth (DBM), is a worldwide major pest of cruciferous vegetables. Because of over-use of insecticides, P. xylostella had developed different levels of resistance to many insecticides and became one of the most serious pests. Metaflumizone is a novel sodium channel blocker insecticide. In China metaflumizone is registered to control diamondback moth and beet armyworm in cabbages.The resistance risk of metaflumizone was assessed by consecutive selection. The resistance was only increased to 2.68-fold after 15 consecutive generations of selection with average morality of 63%. The estimated realized heritability (h2) of metaflumizone resistance was 0.08. It indicated that diamondback moth had low resistance risk towards metaflumizone in 15 generations.Sublethal concentrations of metaflumizone had serious effects on pupation rate, pupal period and pupal weight in parent. And in offspring, the development of eggs, first-instar larvae, pupae and total preoviposition period (TPOP) was seriously influenced. The mean values of intrinsic rate of increase (rm), net reproductive rate (R0), finite rate of increase (λ) had decreased in comparision with the control group. Although sublethal effects were smaller on the offspring, they weren’t eliminated in the first offspring. So in the short term, sublethal doses of metaflumizone may reduce population growth of diamondback moth and don’t stimulated DBM resurgence.A new P450 gene CYP6CV2 from the strain of DBM was cloned with RT-PCR and RACE. The gene was 1613bp in length with an open reading frame of 1368bp encoding 455 amino acid residues.5’-UTR(untranslated region) and 3’-UTR was 52bp and 194bp respectively (Genebank accession No. HQ829967). Analysis of the amino acid sequence indicated the gene had the highest homology with cytochrome P4506 gene family and a maximum similarity to CYP6CV subfamily reached 50%.Using real-time quantitative PCR, mRNA expression of CYP6CV2 was analyzed during different life stages of P. xylostella. The results showed that CYP6CV2 was expressed in all life stages investigated. The relative expression levels appeared in the order of larvae, followed by pupae and adults from high to low. The time-effect and dose-effect of metaflumizone were found in mRNA expression of CYP6CV2. The highest expression levels appeared at 24h with the dosage of LC15 concentration. In LC25 treatments, the expression levels increased continuously in 48h. During the period of peak expression, the relative expression of CYP6CV2 was significantly higher in the treatments than that of in the control groups. It indicated CYP6CV2 gene induced expression was influenced by the treatment time and dosage of metaflumizone.