| Bemisia tabaci（Gennadius）is one of the most invasive pest worldwide,and it is a unique complex species composed of at least 40 cryptic species which are morphologically indistinguishable.In China,there are many native and invasive species of B.tabaci,MED and MEAM1 are two most widely distributed and destructive invasive species.B.tabaci may harbor one primary endosymbiont and seven secondary endosymbionts,which play vital roles in the population spread and invasion.With the rapid proliferation and damage of invasive species of B.tabaci,the study of genetic diversity and genetic structure of different geographic populations about them has become an urgent task.Based on field surveys and systematic collection of B.tabaci across China,we analyzed the variety and distribution of B.tabaci and the population dynamics of invasive species MED and MEAM1 in the past 10 years.Thenafter,the genetic structures of B.tabaci MED and MEAM1 populations were studied based on mtDNA COⅠgene sequence and microsatellite markers.Finally,the diversity of secondary endosymbiont of different B.tabaci cryptic species and collection areas were conducted.The main results of this paper were as followed:（1）Phylogenetic analysis and distribution of B.tabaci in China.We analyzed the B.tabaci samples from 111 regions in 30 provinces across China.Phylogenetic analysis showed that the mtDNA COⅠgene sequences obtained in this study could be clustered with the known cryptic species.We found that the cryptic species distributed in China contained two invasive species,MED and MEAM1,and nine native species including China 1,China 2,China 6,Asia I,Asia II 1,Asia II 3,Asia II 6,Asia II 7 and Asia II 9.Among them,B.tabaci MED were distributed in most parts of China（78.02%）.The next one is MEAM1（11.46%）,which were gradually replaced by MED in the past 10 years but still distributed in some areas.In addition,the native species were distributed in a certain area and even took a dominant position in some areas.（2）Genetic structures of B.tabaci MED and MEAM1 based on mtDNA COⅠgene sequence.The mtDNA COⅠgene was used to analyze the genetic diversity and genetic structure of different geographical populations of B.tabaci MED and MEAM1 in China.The results showed that:Ⅰ,There were variation sites in the mtDNA COⅠgene sequences of the two invasive species（the variation rates were 0.79%and 0.40%,respectively）and all generated obvious A/T bias.Ⅱ,The values of Hd andπof total MED were 0.411 and 0.291,respectively;for each geographic population,the h value ranged from 1 to 5,the Hd value varied from 0 to 1.7845,theπvalue varied from 0 to 0.8000,and the k value ranged from 0 to 2.2254.The values of Hd andπof total MEAM1 were 0.029 and 0.017,respectively;for each geographic population,the h value ranged from 1 to 3,the Hd value varied from 0 to 0.422,theπvalue varied from 0 to 0.381,the k value varied from 0 to 0.824.In addition,nucleotide mismatch analysis showed that B.tabaci MED and MEAM1 were still during a period of expansion or sustained growth.Ⅲ,For different geographical populations of B.tabaci MED,the FST value ranged from-0.875to 1 and the Nm value ranged from 0 to inf.;For different geographical populations of B.tabaci MEAM1,the FST value ranged from-1 to 0.099 and the Nm value ranged from 4.548 to inf.Ⅳ,AMOVA analysis showed that the variation of the two invasive species mainly resulted from the differences among individuals in different geographical populations.Ⅴ,Among the 7 haplotypes of B.tabaci MED,6 haplotypes were shared,of which MED-1（72.26%）and MED-2（25.82%）were dominant shared haplotypes.Among the 4 haplotypes of B.tabaci MEAM1,one haplotype MEAM1-1 was shared haplotype（98.53%）.（3）Genetic structures of B.tabaci MED and MEAM1 based on microsatellite markers.Five microsatellite locus were used as molecular markers to analyze the genetic diversity and genetic structure of B.tabaci MED and MEAM1.The results showed that:Ⅰ,For different geographical populations of B.tabaci MED,the values of Na and Ne were between 2.400 to 4.000 and 1.6348 to2.2822,respectively.The I value ranged from 0.5175 to 0.9238,and the values of Ho and He varied from 0.1800 to 0.4500 and 0.3120 to 0.5446,respectively.The FIS value was between-0.104 and 0.317.Hardy-Weinberg analysis showed that 7 geographical populations deviated significantly from the genetic balance(P（HWE）<0.05).For different geographical populations of B.tabaci MEAM1,the values of Na and Ne were between 2.2000 to 3.4000 and 1.7698 to 2.2473,respectively.The I value ranged from 0.4803 to 0.7362,the values of Ho and He were between 0.2667 to 0.4500 and 0.2728 to 0.4062respectively,and the FIS value was between-0.065 and 0.179.Meanwhile,Hardy-Weinberg analysis showed that only one geographic population significantly deviated from the genetic balance(P（HWE）<0.05).Ⅱ,For B.tabaci MED,the FST value ranged from-0.875 to 1,the Nm value ranged from 0 to inf..For B.tabaci MEAM1,the FST value ranged from-1 to 0.099,the Nm value ranged from 4.548 to inf.Ⅲ,AMOVA analysis showed that the variation of the two invasive species mainly resulted from the differences among individuals in different geographical populations.Ⅳ,Analysis of genetic structure showed that the 22 different geographical populations of B.tabaci MED were divided into two distinct branches,while the 8 different geographic populations of MEAM1 were consistent.（4）Diversity of secondary endosymbionts of B.tabaci.The main single infections of B.tabaci MED were Hamiltonella（95.32%）and Cardinium（22.86%）,and main co-infections were Hamiltonella-Cardinium（22.08%）.However,for B.tabaci MEAM1,the main endosymbionts harboured were Hamiltonella（95.95%）and Rickettsia（45.95%）,meanwhile,Rickettsia-Hamiltonella was the predominat coinfection（33.24%）.Among native species,China 1 and China 2 were mainly infected with Wolbachia,and China 6,Asia I,Asia II 3,Asia II 7 and Asia II 9 were mainly infected with Cardinium,while Asia II 1 and Asia II 6 were mainly infected with Arsenophonus.In addition,the infection of secondary endosymbionts for some cryptic species showed some regional characteristics.In conclusion,the cryptic species of B.tabaci distributed in China mainly contained two invasive species and nine native species,and the geographical distributions of them were quite different and variable.The genetic diversity of MED was higher than that of MEAM1,and the genetic structure of MED was complex,while the genetic structure of MEAM1 was simple.B.tabaci was infected with a variety of secondary endosymbionts,and the infection frequencies varied greatly among different cryptic species and collection areas. |
