| The black locust gall midge,Obolodiplosis robiniae(Haldeman)(Diptera:Cecidomyiidae),native to North America,was a serious defoliator attacking Robinia pseudoacacia(Fabaceae).It was first recorded in Qinhuangdao City,Hebei Province in 2004 by Yang et al.(2006),but spread rapidly in the last decade and now distributed in many areas in China.In destructed region,the gall midge can get 100% infection rate,and result in a big economic loss.For discussing the genetic mechanism associated to colonization and figuring out population differentiation during expansion,we analyzed geographic population genetic diversities and structures of O.robiniae based on mitochondrial DNA sequence(COI)and microsatellite DNA markers.The main results are as follows:(1)We clearified the distribution range of the gall midge for the first time.It includes 30 cities of 17 provinces in China,with east longitude being from 26.33° to 43.53°,north latitude from 104.07° to 125.16° and the elevation from 5 m to 1460 m.Which is consistent with the distribution of R.pseudoacacia(25°-44° N,102°-125° E,5-1460 m).(2)An analysis of a 676 bp sequence of the mitochondrial DNA cytochrome oxidase subunit I was conducted in 560 individuals from 28 populations.Only three substitutions(distributed in DD ? DY and TA)and four haplotypes were identified,and the nucleotide diversity was low(? = 0.00005).The result showed a low degree of genetic diversity among populations of the successful invasive gall midge.(3)Microsatellite markers of O.robiniae were developed by bead enrichment.Fourteen loci were found to be polymorphism,with the number of alleles ranging from 3 to 10.The observed heterozygosity varied evenly from 0.2667 to 0.6540.For populations,the observed heterozygosity ranged from 0.1429 to 1.000.The allele frequency of the predominant allele varied from 0.250 to 0.500.These markers might represent a useful tool in the study of population evolution in this important introduced pest.(4)The effect and the correlation between the sample size and the genetic diversity index of population of O.robiniae was analyzed based on microsatellite DNA data.Totally 12 grades of sample size were designed.The result showed each index was going to steady when the sample size was over 20,and the better parameters were He and H,if specimens were enough.(5)Fourteen microsatellite loci from above the third item was used to discuss the population genetic structure of the gall midge from 22 locations in China.Only 11 loci showed polymorphism,with the number of allele and the number of effective allele varied from 1-9and 1-7,observed heterozygosity and expected heterozygosityfrom 0.23-0.75 and 0.29-0.88 respectively,and polymorphic information content from 0.24-0.86,which reflected 22 populations of O.robiniae on each locus was with high genetic diversity and these 11 loci can really reflect population genetic mutation.The UPGMA cluster analyses displayed that 3 large groups were formed among 22 populations. |
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