Identification Of Cryptic Species Of Bemisia Tabaci(Gennadius) And Population Genetic Structure Of MED And Meam1 Based On Double Genes, MtDNA COI And RDNA ITS1 Markers

Bemisia tabaci(Gennadius)(Hemiptera: Aleyrodidae), one kind of global agricultural pest, is a species complex made up of more than 30 cryptic species. MEAM1 and MED, two cryptic species of the complex, had invaded most provinces in China and in many areas successfully replaced indigenous cryptic species which didn’t cause significant damage. We concentrated on the question that cryptic species of Bemisia tabaci are too morphologically similar to be distinguished quickly and study the effectiveness of mtDNA COI and rDNA ITS1 genes used on the identification of Bemisia tabaci by analyzing DNA sequences and phylogeny between the cryptic species. The population genetic structures of MED and MEAM1 were also explored. The specific results of the research are as follows.(1) Feasibility analysis on the identification of Bemisia tabaci based on mtDNA COI and rDNA ITS1 double genes. The average inter-cryptic species genetic distance was 27.8(0.1502 vs. 0.0054) and 7.5(0.0328 vs. 0.0044) times higher than the corresponding average intra-cryptic species genetic distance for mtDNA COI gene and rDNA ITS1 gene, respectively. There was no overlap between the inter- and intra- cryptic species genetic distances when mtDNA COI gene was analyzed, while overlap was observed when rDNA ITS1 gene was analyzed. Phylogenetic trees(NJ tree and ML tree) based on mtDNA COI gene showed that all of the nine cryptic species could form respectively independent evolution branches. However, phylogenetic trees(NJ tree and ML tree) based on rDNA ITS1 gene showed that only Asia II 3 and Asia I could form independent evolution branches while others could not. Identification of cryptic species of Bemisia tabaci based on mtDNA COI gene is more accurate and more reliable than that based on rDNA ITS1 gene. 647 COI gene sequences of 13 cryptic species and 636 ITS1 gene sequences of 12 cryptic species from this research and GenBank database were entered into Database of Invasive Alien Species in China, providing technical support and a platform for the remote identification of Bemisia tabaci.(2) Research on the population genetic structure of Bemisia tabaci MED cryptic species. Haplotype diversity(Hd) and nucleotide diversity(π) of all populations were 0.599 and 0.00170 based on COI gene, while the values were 0.520 and 0.00129 based on ITS1 gene. It means that genetic diversity of MED is at the moderate level. Fu’s Fs were-21.031(based on COI gene) and-4.701(based on ITS1 gene), indicating that MED in China had undergone population expansion in the past. Fst(0.16204) and Nm(1.29) based on COI gene indicated that moderate level of genetic divergency and high level of gene flow had already happened among different MED geographical populations in China. However, Fst(0.02628) and Nm(9.26) based on ITS1 gene represented non-significant genetic divergency and high level of gene flow, which were inconsistent with the analysis of COI gene. We came to the conclusion that geographical isolation was not the dominant factor of causing genetic divergency between different MED geographic populations in China from the results of AMOVA and phylogenetic relationships between haplotypes of COI and ITS1 genes, respectively. Haplotypes of MED cryptic species from China were integrated with those from GenBank database and phylogenetic analyses was processed. We speculated that MED cryptic species in China might originate from Americas, Africa, Mediterranean region, Western and Northwestern Europe and other regions.(3) Research on the population genetic structure of Bemisia tabaci MEAM1 cryptic species. Haplotype diversity(Hd) and nucleotide diversity(π) of all populations were 0.414 and 0.00063 based on COI gene, while the values were 0.166 and 0.00168 based on ITS1 gene. It means that genetic diversity of MEAM1 is at a low level that its population development would be hindered. Fu’s Fs were-6.422(based on COI gene) and-1.694(based on ITS1 gene), indicating that MEAM1 in China had undergone population expansion in the past. Fst(0.58990) and Nm(0.17) based on COI gene indicated that significant genetic divergency had already happened among different MEAM1 geographical populations in China due to the genetic drift, while Fst(0.01037) and Nm(23.86) based on ITS1 gene represented low level of genetic divergency and high level of gene flow. We came to the conclusion that geographical isolation was not the dominant factor of causing genetic divergency between different MEAM1 geographical populations in China from the results of AMOVA and phylogenetic relationships between haplotypes of COI and ITS1 genes, respectively. Haplotypes of MEAM1 cryptic species from China were integrated with those from GenBank database and phylogenetic analyses was processed. We speculated that MEAM1 cryptic species in China might originate from Mediterranean region, Western Europe, Americas, South and Southeast Asia and other regions.The results of this study will make a contribution to the accurate identification and effective control of Bemisia tabaci to protect the safety of national agricultural production. They also provide theoretical basis for exploring the source and mechanism of invasion, propagation mode, mechanism of replacement and the construction of a comprehensive prevention and control system.