Inheritance Mode, Cross Resistance And Resistance Mechanisms Of A Fipronil-Resistant Strain Of Plutella Xylostella (L.)

The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is aneconomically important pest of crucifer vegetables throughout the world. Integrated pestmanagement programs are currently indispensable for the control of P. xylostella. However,the indiscriminate use of insecticides, the multiple generations per annum and the highmigratory potential of the species have led to the development of resistance to majorinsecticide groups.Fipronil is an outstanding phenylpyrazole insecticide for crop protection. Theinsecticide action involves blocking the neuron-inhibitory GABA-gated chloride channel.This study was aimed to investigate the inheritance mode, cross resistance and resistancemechanisms of a fipronil-selected strain of P. xylostella.1. Inheritance mode of fipronil resistance in the SZ-F strain of P. xylostellaThe fipronil-resistant SZ-F strain and the susceptible ROTH strain were used forreciprocal crosses and backcrosses. The SZ-F strain had 493.5 fold resistance to fipronilcompared with the ROTH strain. The progenies from reciprocol crosses showed 108.2-and100.2-fold resistance to fipronil, indicating fipronil resistance in the SZ-F strain wasincompletely dominant and inherited as a dominant trait. The values of dominance levelwere between 0.51 and 0.49 (by Stone formula). In the LD-P curve of fipronil in thebackcross progeny, there was a distinct plateau corresponding to 50% mortality. Thisplateau suggests that fipronil resistance may be controlled by one gene. The x~2 test of thegoodness of fit between the observation and predictions under the assumption of monofactorial inheritance further supported the single-gene hypothesis.2. Cross-resistance pattern of the fipronil-resistant SZ-F strain of P. xylostellaThe SZ-F strain showed 482.8-fold resistance compared with the SZ strain. However,the SZ-F strain did not show any cross resistance to abamectin, spinosad, monosultap,chlorfenapyr, cypermethrinand, chlorpyrifos, indoxacard and metaflumizone. It suggeststhat proper used of mixture or rotation between these insecticides could slow downresistance development to fipronil in the field.3. Metabilic enzyme activities of the fipronil-resistant and susceptible strains of P.xylostellaDetoxication enzymes including monooxygenases (PNOD and MCOD), glutathioneS-transferases (DCNB, CDNB), and general esterases were compared among the ROTH,SZ and SZ-F strains. There was no correlation between metabolic enzyme activities andfipronil resistance. The synergism ratios of PBO, TPP, DEF and DEM to fipronil in SZ-Fstrain were similar (0.93-, 1.01-, 1.89-, 1.54-fold, respectively), suggesting metabolicdetoxification probably confers inherent tolerance in the SZ-F strain. Enhanced metabolicmechanism may not be involved in fipronil resistance in the SZ-F strain of P. xylostella.4. Detection of the mutation in PxRdi geneA genotyping technique for the A302S mutation in the PxRdl alleles in individuallarvae was developed based on the direct sequencing chromatogram of the target PCRfragment. The mutation PxRdl-Ser allele frequency in the SZ-F strain was 30ï¼…, however, itwas not found in SZ and Roth strain. After a treatment of 20 mg/L fipronil on the SZ-Fstrain, the PxRdl-Ser allele frequency in the survivors increased to 57ï¼…. High frequency ofthe PxRdl-Ala allele remaining in the resistant SZ-F strain suggested that the A302Smutation in the PxRdl gene is partially associated with fipronil resistance and that othermutation(s) in the PxRdl gene or other Rdl-like subunit(s) may contribute to fipronilresistance.