Study On The Occurrence And Genetic Diversity Of Spodoptera Litura In Guangxi

Spodoptera litura（Fabricius）（Lepidoptera:Noctuidae）is an important agricultural pest that is widely distributed around the world.The pest is one of the main pests on tobacco in Guangxi with the characteristics of clustering,concealment,overeating and diffusivity.In this study,the occurrence dynamics of S.litura in Guangxi was investigated by means of systematic investigation,field survey and sex attractant trapping.Genetic diversity and genetic structure of 24 different geographical populations and 8 different host populations of S.litura in Guangxi were studied by microsatellite molecular marker technology.These studies will be helpful to understand the occurrence dynamics of S.litura in local areas,providing a theoretical basis for diffusion blocking and control.The main results are as follows.1 Study on the occurrence of S.litura in Guangxi tobacco areaSystem investigation,field census and sexual attractant trapping were conducted in Jingxi City and Fuchuan County,Guangxi,for two consecutive years from 2021 to2022 during the growth and development of tobacco.The results showed that there were two peaks of S.litura larvae in the systematic survey of Jingxi City in 2021,which were in early May（54 larvae per 100 plants）and early June（84 larvae per 100plants）,respectively.The number of S.litura larvae in the three field surveys in other towns was 3,24.8 and 58.8 larvae per 100 plants,respectively.There were three peaks in 2022,which were in early April（10 larvae per 100 plants）,early May（94 larvae per 100 plants）and late June（64 larvae per 100 plants）,which represented 0,0 and2.3 larvae per 100 plants in the three field surveys in other towns.There were two peaks of S.litura larvae in Fuchuan County.In 2021,it was in early June（16 larvae per 100 plants）and early July（4 larvae per 100 plants）,respectively.The number of S.litura larvae in the three field surveys in other towns was 0.8,2 and 2.7 larvae per 100plants,respectively.In 2022,it was in late May（45 larvae/100 plants）and late June（24 larvae/100 plants）,respectively.The number of S.litura larvae in the three field surveys in other towns was 0,8.2 and 12.7 larvae per 100 plants,respectively.There were three peak periods of S.litura adults in Jingxi City and Fuchuan County in 2022.The peak periods of adults in Jingxi City were in late March（40 larvaes）,middle May（29 larvaes）and middle June（33 larvaes）,respectively.The peak periods of adults in Fuchuan County were in early May（84 larvaes）,late June（62 larvaes）and middle July（35 larvaes）,respectively.2 Study on genetic diversity of different geographic populations of S.litura in GuangxiSeven pairs of microsatellite primers were used to study the genetic diversity and genetic structure of 24 geographical populations of S.litura in Guangxi.The results showed that seven pairs of microsatellite primers detected 83 alleles in 545 S.litura larvae with certain polymorphism.The number of alleles（Na）of 24 populations ranged from 4.14 to 6.86,the polymorphic information content（PIC）of all populations was greater than 0.5.The mean number of observed heterogeneity（H_O）,expected heterozygosity（H_E）was 0.4793 and 0.5970,respectively.The allele richness（A_R）averaged 5.1439,and the average of Shannon’s index（I）was 1.2342.The above data indicated that different geographical populations of S.litura were rich in genetic diversity.The genetic structure analysis showed that there was no clear geographical grouping pattern among populations,and different geographical populations were mainly mixed;the fixed coefficients(F_ST)ranged from 0.013-0.130,with low to moderate differentiation among populations;The results of AMOVA analysis showed that genetic variation was mainly among individuals（78.06%）,and the level of variation between populations was low（1.92%）;Mental test revealed no significant correlation between the genetic and geographical distances of populations.These results suggest that frequent genetic exchange among populations of S.litura,long-distance migration and dispersal lead to low genetic variation in population structure,resulting in random mating populations.3 Study on genetic diversity of different host populations of S.litura in GuangxiSeven pairs of microsatellite primers were used to analyze genetic diversity and structure of eight host populations（tobacco,taro,peanut,soybean,corn,sweet potato,pepper and garden sorrel）.The results showed that the number of alleles（Na）of eight populations ranged from 2.43 to 6.14,and the mean effective number of alleles（Ne）was 3.1788.The number of effective alleles of host garden sorrel（SM）was the smallest,1.9027.The mean polymorphism information contents（PIC）and Shannon’s index（I）were 0.4574 and 1.1543,respectively.Observed heterogeneity（H_O）and expected expected heterozygosity（H_E）ranged from 0.4081-0.5816 and 0.3948-0.6124,respectively.The expected heterozygosity of all host populations was greater than observed heterozygosity except for host garden sorrel and soybean that the expected heterozygosity was smaller than observed heterozygosity.These data indicated that genetic diversity of different host populations was relatively rich.Based on Bayesian clustering,NJ phylogenetic tree and PCo A genetic structure analysis,it was concluded that there were certain genetic structure among different host populations,which could be roughly divided into four genetic groups.Tobacco and pepper populations were the first group,garden sorrel populations were the second group,taro,soybean,peanut and corn populations were the third group,and sweet potato populations were the fourth group.The fixed coefficient(F_ST)between populations ranged from 0.010-0.208,and genetic differentiation was low to high among populations.The genetic differentiation of corn and peanut populations was the least,while soybean and garden sorrel populations was the largest.