Study On Trapped Dynamics And Genetic Structure Among Different Geographic Populations Of Spodoptera Litura

The common cutworm,Spodoptera litura(Fabricius)(Lepidoptera: Noctuidae)is an important agricultural pest causing enormous losses to many economically important crops.The larva is polyphagous with more than 112 cultivated plants,including cotton,groundnut,tobacco,soybean,and various vegetables recorded as hosts.In Yunnan,Guangxi,Guangdong,Hainan,Fujian and Taiwan,it can occur 8-9 generations in a year,and it can be seen in some areas of the Yangtze River,especially in 4-5 generations.In the Yellow River basin,4-5 generations occur every year,in which July-September occurred seriously.Migration behavior is a kind of selection strategy of avoiding unsuitable living environment formed by insects in the long evolution process.Migratory pests were often caused sudden outbreaks in different areas and brings disastrous losses to local agricultural production.Therefore,the study on migration behavior of Spodoptera litura is helpful to understand the regularity of the pest,and to provide a theoretical basis for further accurate prediction and comprehensive management of large area.This study on the migration of S.litura from the macro and micro two aspects were systematically done.On macro,searchlight trapping observations provide the population dynamics of S.litura in Wuhan(WH),Langfang(LF)and Changdao(CD).At the same time,using high-altitude searchlight trap the S.litura in Wuhan,Langfang,and long island,statistics of the three trapping population of seasonal population dynamics,sex ratios,ovarian development level of female moths,mating rate,and juvenile hormone content of female moths were examined.On micro,the population differentiation and genetic diversity of eighteen S.litura populations from different districts by using SSR and AFLP markers.The main results are as follows:1.Searchlight trapping observations provide the population dynamics of S.litura in Wuhan(WH)and Langfang(LF)from 2009-2013.There was no considerable inter-year variability of population dynamics for S.litura caught at Wuhan station from May to November in 2009-2011 and 2013,with a maximum of 766 captured in 2013 and a minimum of 402 in 2011.Generally two noticeable peaks of flight activity were obtained in August and October.There was also no considerable inter-year variabilityof population dynamics for S.litura caught at Langfang station from May to October in 2011-2013,with a maximum of 328 captured in 2013 and a minimum of 213 in 2011.Generally one noticeable peak of flight activity was obtained in the fall.The degree of ovarian development from Wuhan showed significant intra-and inter-month variability,with a significant year ×month interaction.The incidence of mating from Wuhan showed significant intra-and inter-month variability.In all years,the vast majority of female S.litura were in level 3-4 from May to July.In August and September,the overall the degree of ovarian development and the incidence of mating were somewhat less than for July.In October and November,the majority of females captured showed minimal ovarian development and mating was few.The degree of ovarian development and the incidence of mating from Langfang showed significant year ×month interaction variability in both analyses.In all years,there were no moths captured from May to July.In 2011 and 2012,the vast majority of female S.litura were in level 3-5 from August to October.In 2013,the propotion of females in level 1-2 rised from August to October.However,the incidence of mating decreased from greater than 90% to about 40%.2.Juvenile hormone(JH)is an important control factor in insect reproduction and migration.JH titers of S.litura caught at Langfang(LF)and Changdao(CD)stations were lower than those of S.litura caught at Wuhan(WH)station.JH titers of S.litura caught in 2009-2011 had the tendency of decrease from May to November,but JH titers of S.litura caught at Changdao(CD)station had the tendency of increase from May to November.JH titers of S.litura caught at Langfang(LF)station were low,and had no fluctuation.3.Practical microsatellite system for Spodoptera litura population studies was developed.Six polymorphic SSR loci were estimated by Gene Scan sequencing technology.We observed 162 alleles in 9 microsatellite loci from 18 populations.The observed and effective number of alleles per locus ranged from 5 to 34 and from 1.23 to 9.16 for the nine loci,respectively.The mean Shannon's information index was 1.6,and the average observed(Ho)and expected(HE)heterozygosity in all populations was from 0.18 to 0.98 and from 0.17 to 0.86,respectively.The mean allelic richness(AR)was 3.93 and the mean polymorphism information content(PIC)was 0.64.This shows that the genetic diversity of Spodoptera litura populations is high.Two loci(CWM-1 and CWM-4)of 9 showed deviation from Hardy-Weinberg predictions(exact probability test,P<0.05).Heterozygosity deficit of CWM-4 were caused by the small number of individuals sampled because successful PCR amplification was obtained in tested samples;however,another locus(CWM-1)appeared to be due to null allele.The genotypic data showed significant linkage disequilibrium between pairs of loci(P>0.05).The overall Fst is 0.05,and the estimated value of gene flow from Gst was 8.8724.Analysis of Nei`s genetic diversity showed that there was a low level of genetic differentiation among populaitons with a considerable frequency of gene flow.4.The genetic diversity and genetic structure of Spodoptera litura from 17 populations(totally 408 individuals)were examined using AFLP method.Six pairs of selective primers from 64 pairs of primere combinations were used to AFLP amplify the total DNA of Spodoptera litura samples.The primers yielded a total of 157 scorable loci,of which 100% loci were polymorphic.The Nei's gene diversity index from 0.18 to 0.3114,and Shannon's index from 0.2559 to 0.4438.Analysis of Nei`s genetic diversity showed that there was a high level of population genetic structure with a considerable frequency of gene flow.Phylogenic trees reconstructed from the microsatellite and AFLP data indicated that 18 populations grouped without correlation with their biological distribution.NJ and UPGMA trees analysis showed that 18 populations grouped into two major branches.One is along with a coastal way,and other is along with NC(North China)– Wushan – Hengduan mountains.