Monitoring Of Resistance Level Of Spodoptera Frugiperda To Lambda-cyhalothrin And Indoxacarb In 16 Provinces Of China From 2019 To 2020

Spodoptera frugiperda is a major omnivorous agricultural pest,which has the characteristics of strong long-distance migration,strong reproductive ability,strong adaptability and gluttony.It was listed as one of the top ten plant pests in the world by the International Agricultural and Bioscience Center（CABI）in 2017.In December 2018,S.frugiperda invaded Yunnan Province for the first time and spread rapidly.At present,chemical control is the main means to control S.frugiperda,but the problem of insecticides resistance is becoming increasingly prominent.This paper focuses on the Monitoring of resistance level of S.frugiperda to lambda-cyhalothrin and indoxacarb in 16 provinces of China from 2019 to 2020.The specific results are as follows:1.According to the single-nucleotide polymorphisms at e4₁₈₃site of the Tpi gene,corn strain and rice strain were identified.Among the 980 individualsin 2019,there were 980 corn-strain individuals,accounting for 98.9%;only 7 rice-strain individuals,accounting for 0.7%;and 4 heterozygous individuals,accounting for 0.4%.In 2020,1027 individuals of the field population of S.frugiperda in16 provinces of China were corn-strain homozygotes,and rice-strain and heterozygote were not detected.The results of larval selective feeding experiment showed that among the 1036 individuals in16 provinces in 2019,the proportion of 1030 larvae feeding on corn leaves was 99.42%;Only 6 larvae chose to feed on rice leaves,and the proportion was only 0.58%..In 2020,912 larvae feed on corn leaves,accounting for 99.78%;Only 2 larvae chose to feed on rice leaves,and the proportion was only 0.27%.Combined with the results of molecular detection and larval selective feeding experiment,the results showed that there were orn strain,rice strain and heterozygous type in the invading S.frugiperda in China,and corn strain was the main part.2.Through the comparative analysis of the bioassay of the 3rd instar larvae reared in the field of S.frugiperda in 16 provinces of China in 2019,it was found that the b value range of the topical application method was 1.2～3.5,which was larger than that of the leaf dipping method,0.8～2.7.the value ofc2 of the topical application method was significantly lower than that of the leaf dipping method,and the P value was relatively concentrated,between 0.8489 and 0.9999.Compared with the leaf dipping method,the dispersion of the bioassay data of the topical application method is smaller,and the genetic purity of the population is higher,so the topical application method is more suitable for the bioassay of S.frugiperda.3.The results of monitoring the resistance level of S.frugiperda to lambda-cyhalothrin in 2019 and2020 showed that:In 2019,Guangxi population had the highest sensitivity to lambda-cyhalothrin(LD₅₀=12.523μg/g);16 populations had a resistance ratio of 1.0～4.3 times to lambda-cyhalothrin.And Hunan population had the highest sensitivity to lambda-cyhalothrin in 2020(LD₅₀=14.593μg/g);16populations had a resistance ratio of 1.1～4.2 times to lambda-cyhalothrin,.Combined with the data of two years,it can be inferred that the population of S.frugiperda invading China has medium level resistance to cyhalothrin,and cyhalothrin insecticide can be used reasonably in field control.4.The results of monitoring the resistance level of S.frugiperda to indoxacarb in 2019 and 2020showed that:In 2019,Sichuan population had the highest sensitivity to indoxacarb,with a median lethal dose of 4.419μg/g and 16 populations had a resistance ratio of 0.9～3.4 in 2019;Guizhou had the highest sensitivity to indoxacarb(LD₅₀=7.235μg/g)in 2020 and 16 populations had a resistance ratio of 1.5～5.1 to indoxacarb.The results showed that the population of S.frugiperda invading China had low resistance to indoxacarb.It is suggested that indoxacarb can be used reasonably in field control and should be used in conjunction with effective synergists.At the same time,resistance monitoring in fields should be further strengthened to slow down the development of indoxacarb resistance.5.Through molecular detection of the genotypes of VGSC in field populations of S.frugiperda in2019 and 2020,no mutation was detected at site 932 in 1656 individuals in 2019 and 929 individuals from 16 provinces in 2020.At site 929,a total of 3 individuals were detected as resistant heterozygous genotype and the mutation frequency of resistance gene was 0.2%in 2019,but no mutants were detected in 2020.At the same time,at site 1014,no mutant was detected in 2019,while 4 of 929 individuals in 2020 were resistant homozygous genotype,and the mutation frequency of resistance gene was 0.4%.