| Platygaster robiniae Buhl et Duso(Hymenoptera: Platygastridae)is an important and specialized natural enemy of the black locust gall midge Obolodiplosis robiniae(Diptera:Cecidomyiidae)which is an invasive insect pest in China.It is a koinobiont endo-parasitoid attacking the egg-larvae stage of its host.In the natural condition,the parasitism ratio is over80%,so the agent plays a significant role to decrease the population of its host.In past more than ten years,P.robiniae and its host O.robiniae both together have been highly noted in the world since that the host had been introducing into Europe and Asia.It was firstly named and described by Buhl and Duso in 2008 via examining specimens from Italy,Japan and Czekh.Then,it was found in other European and Asian countries and regions where its host O.robiniae infected.In China,the parasitoid was firstly found in 2010 in Qinhuangdao city where its host was first discovered.For the newly known species,the genetic diversity and structure exploring might be helpful to know what its genetic differentiation and gene flow are,as well as acquaint what the phylogenic relationship among the populations is.In this study,the microsatellite DNA markers were used to analyze the genetic structure and variation characteristics of 22 populations of P.robiniae in China.The conclusions are follows as below.(1)The distribution range of P.robiniae was firstly figured out in China.Here we investigated the parasitoid in 17 provinces containing 29 regions.The result showed the geographic distribution range of the parasitoid is N:26°35.451′-43°53.482′,E:103°51.816′-125°15.969′,altitude: 4-1097 m.The range includes North China,Northeast,northern Central China,northern South China,northern Southwest and eastern Northwest.The distribution range is similar to that of its host O.robiniae.(2)The microsatellite primers were newly and successfully developed by next generation sequencing via scanning mitochondrial genome of P.robiniae.Over 130000 SSR loci of the P.robiniae were found in mitochondrial genome sequencing.The primers polymorphism wastested in 48 individuals of P.robiniae adults,and 37 markers were finally selected for proper PCR conditions fixed.After tested,the primers size crosses 147-442 bp,the average size of fragment is 261 bp,the numbers of alleles are from 2 to 8,the observed Heterozygosity are from 0.00 to 0.96,the expected Heterozygosity are 0.04-0.70,the allele frequency are0.13-0.50.Those loci are certainly necessary and a solid foundation for the following populations diversity study.(3)Twenty-six pairs of microsatellite primers were used to analyze the genetic diversity of22 populations of P.robiniae in China.The microsatellite parameters of P.robiniae showed that those populations revealed high genetic diversity in all loci.The numbers of alleles are 1-9,the effective numbers of alleles are 1.00-4.10,the observed Heterozygosity are 0.24-0.78,the expected Heterozygosity are 0.01-0.62 and polymorphism information content are 0.23-0.75.(4)The 22 populations of P.robiniae were clustered into four big clades based on UPGMA phylogeny tree.In the view of clades,no significant divisions geographically were found in the whole distribution range.The reason may be human being interference like trade activities and travels was helpful for spread of the wasp,which results to the different population making gene flow.However,in the part of regions,some populations of P.robiniae clustered together in the light of geographical location,such as four populations of Bohai Bay region containing Dandong(DD),Yingkou(YK),Dalian(DL)and Qinhuangdao(QH),clustered together;three populations of Southwest region containing Chengdu(CD),Tianshui(TS)and Yanchuan(YC),clustered together;Norhteast region containing Changchun(CC)and Shenyang(SY),clustered together. |
