Variance Of Knockdown Resistance Allele Frequency In Plutella Xylostella (Linn) In Different Instar Larvae, Different Seasons And Different Localities

The diamondback moth (DBM), Plutella xylostella (Linn.), is a destructive pest incruciferous vegetables throughout the world and has evolved serious insecticide resistance toover50insecticides. The point mutation in Na+channel gene is an important mechanismunderlying the knockdown resistance evolution. Based on the accuracy and repetitivity ofdetection results, the2detection methods PASA and DNA sequencing, were compared and DNAsequencing was proven better. By means of DNA sequencing, the variance of knockdownresistance allele frequency in DBM in different instar larvae, different seasons and differentlocalities was investigated. The main results were as follows:(1)Establishment of procedure for knockdown resistance monitoring in P. xylostellaIt was demonstrated that the accuracy of the detection results by means of PASA was verylow. Meanwhile, for the DNA sequencing procedure, take MT1MT2and LF1LF2as primersto amplify DNA fragments encoding sodium channel containing the T929I, M918T mutationsand the L1014F mutations, respectively. The PCR products were about470bp in size and nononspecific fragments were amplified.(2)Effect of knockdown resistance on the toxicity of fenvalerate insecticide to the4^thinstarlarvae of P. xylostellaThe LC₅₀of the4thinstar larvae of DBM, reared in Institute of Plant Protection, FujianAgricultural Academy, to fenvalerate was912.3mg/L. According to the detection results, bothknockdown resistance allele frequencies were98.33%. Because of this, the gene type of the deadindividuals after fenvalerate treatment at any concentrations was resistant homozygote. Socompared with target mutation, other factors played an more important role in knockdownresistance evolution of DBM.(3)Effect of instar and season on knockdown resistance allele frequency of P. xylostellaThe knockdown resistance allele frequency of DBM in2^nd,3^rdand4^thinstar larvae weredetected and the results demonstrated that knockdown resistance allele frequencies in differentinstar larvae were all over98%. Similarly, knockdown resistance allele frequencies in thefield population in different seasons varied little, either.(4)Knockdown resistance allele frequency detection of P. xylostella from different localities The DBM were collected from9localities of4provinces (Fujian, Nei menggu, Zhejiang,Beijing), and knockdown resistance allele frequency were detected. No M918T mutations werefound which indicated that the super-knockdown resistance has not evolved in all the localities.But allele frequencies for T929I and L1014F were over90%and only one susceptiblehomozygote for T929I was found in the individuals collected from Xiekeng.