| Sirex noctilio F.(Hymenoptera: Siricidae: Siricinae)is a major quarantine pest of forestry in the world.It is native to Eurasia and North Africa and has been introduced into all continents within the last 120 years,except Antarctica.Since 2013 when it was first recorded in China it has caused serious harm to the Pinus sylvestris var.mongolica forest and has the potential harm to other Pinus in China.In this study,a rapid identification technique for Sirex noctilio was developed,which can meet the needs of inspection and quarantine.By comparing and analyzing the genetic characteristics of the Chinese Sirex noctilio population with that of the native woodwasp Sirex nitobei,as well as other Sirex noctilio populations from abroad using mitochondrial and microsatellite markers.The source and spread patterns of the Chinese Sirex noctilio population was then retraced.Finally,a simulation of the distribution of Sirex noctilio under future climatic conditions in China and around the world was carried out using distributional and climatic data.The purpose of this study was to provide theoretical and technical support for the early detection and early warning of the presence of Sirex noctilio.The main results are as follows:1.Species specific primers for Sirex noctilio were developed which had strong specificity,good stability and high sensitivity,and could be used for the rapid identification during inspection and quarantine process.The morphology of Sirex larva is quite similar,and it is difficult to identify the nonadult stages.In order to solve the problem,the base sequences of 17 species of woodwasps were analyzed,and a pair of SS-COⅠ primers was designed.Five other species of Siricidae in China were used as controls,as well as three different stages(larva,pupa and adult),16 different geographical populations and different concentration of DNA of Sirex noctilio.2.There were significant differences in the genetic characteristics between Sirex noctilio and the Chinese native woodwasp Sirex nitobei which showed that Sirex noctilio was an invasive species.The population genetics of Sirex noctilio and its relative species Sirex nitobei were compared.The results of genetic diversity showed that for Sirex noctilio,the ratio of variation sites in the COI sequence was 3.03%,the number of haplotypes was 13,the diversity of haplotypes(h)was 0.3550,and the diversity of nucleotides(π)was 0.0012.By contrast,for Sirex nitobei,the ratio of variation sites in the COI sequence was 9.44%,the number of haplotypes was 64,the diversity of haplotypes(h)was 0.8070,and the diversity of nucleotides(π)was 0.0067.The results on the genetic characteristics showed that the diversity of haplotypes in Sirex noctilio population was low(h=0～0.5630,Mean=0.1381).There was obvious genetic differentiation among different haplotypes,and each haplotype exhibited obvious geographical distribution pattern.However,the diversity of haplotypes in Sirex nitobei was high(h=0～1,Mean=0.6196).There was no obvious genetic differentiation among different haplotypes,and the geographical division of genes was not obvious.This indicate that Sirex noctilio was an invasive species.3.Chinese Sirex noctilio population could be divided into two groups: a northwestern and southeastern group,which may have originated from at least two independent invasions.Mitochondrial and microsatellite markers were used to analyze the genetic characteristics of different geographical populations of Sirex noctilio in China.The results of AMOVA and Structure showed that the Chinese Sirex noctilio population was made up of two groups: a northwestern and southeastern group.The AMOVA results also supported the groupings done based on distance and environment(among groups: 38.64%>among populations within groups: 9.15%,P≤0.01)and also by latitude(among groups: 25.58%> among populations within groups: 22.46%,P≤0.01).The geographical distribution of haplotypes was consistent with this grouping mode.Eight pairs of microsatellite loci(PIC=0.2782～0.7881)with medium and high polymorphisms were used to mark the samples.The results of Structure showed that the Chinese Sirex noctilio population was divided into two clusters(Cluster1 and Cluster2).There was obvious differentiation of geographical structure between these two clusters.Cluster 2(93.7583%)dominated in the northwest,whereas cluster 1(67.5390%)dominated in the southeast,and the genetic differentiation coefficient(Fst)between the two groups was 0.6667,with a high degree of genetic differentiation(Fst > 0.25).The results of haplotype phylogeny of Sirex noctilio in the world showed that the populations in the northwest of China(Manzhouli,Huoduqi,Honghuaerji)may have come from Europe and South America;the remaining populations in the southeast may have come from all continents,especially from North America and Europe.4.Chinese Sirex noctilio populations went under rapid expansion,and their southward spread was influenced by human activities.Mitochondrial COI marker was used to analyze the genetic characteristics of the global Sirex noctilio populations.The values of the genetic structure characteristics(sample number,haplotype number,sample size per haplotype)of European populations,North American invasion populations and Chinese new invasion populations were respectively: Europe(44,4,ratio 11),North America(39,2,ratio 19)and China(193,8,ratio 24).The values of the genetic diversity parameters in European native populations(h=0.533,π=0.00194)were significantly higher than those in North America(h=0.264,π=0.00082)and in China(h=0.311,π=0.00114).The increase in the ratio of individuals per haplotype in China was stronger than that in North America,and the decrease of genetic diversity was weaker than that in North America.This showed that the population of Chinese Sirex noctilio had rapid expansion process after the bottleneck effect.The results of Mantel test showed that genetic distance was significantly correlated with geographical distance(r=0.38878,p<0.01);Some populations with large geographical distance(such as the distance between Manzhouli and Changchun of 878 km with the Fst=-0.2039;the distance between Changchun and Chifeng of 544 km with the Fst=-0.0727)had no genetic differentiation(Fst < 0.05);The genetic diversity of the southern population(Jinbaotun population: h = 0,π=0)found in 2016 was lower than that of the northern population(Dumeng population: h=0.549,π=0.00183)found in 2013.Based on features identified in damaged areas and the sampling time of various populations,it was inferred that the Chinese Sirex noctilio populations had experienced a southward diffusion which was influenced by human activities.5.Prediction results from the maximum entropy model showed that the suitable areas of Sirex noctilio was mainly distributed between 30°N-60°N and 25°S-55°S.Annual average temperature was the most important environmental factor affecting the global distribution of Sirex noctilio among many meteorological factors.The suitable areas of Sirex noctilio accounted for 26% of global land area which included New Zealand,Australia,South Africa,Brazil,the United States,China,France and the United Kingdom.The new distribution points of Sirex noctilio found in China were all located in the highly suitable area. |
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