Detection Of Wolbachia In Two Rice Pyralids And Sequence Analysis Of Complete Mitochondrial Genomes Of Three Rice Pests

Chilo suppressalis (Walker)(Lepidoptera:Pyralidae) and Cnaphalocrocis medialis (Guenee)(Lepidoptera:Pyralidae), and Sesamia inferens (Walker)(Lepidoptera:Noctuidae) are famous rice pests, in which C. suppressalis and S. inferens are wood-boring insects, C. medialis is a migratory pest. In this study we investigate prevalence and diversity of Wolbachia infection in C. suppressalis and C medialis populations. Meanwhile, the complete mitochondrial genomes (mitogenomes) of C. suppressalis, C. medialis, and S. inferens were sequenced and analyzed, which can enrich the lepidopteran species data in Genbank and go further into declare the phylogenetic relationships among lepidopteran insects. The primary achievements of this dissertation were listed as follows:1. Infection frequency of Wolbachia in23populations of C. suppressalis ranges from0-40.0%with an average infection rate at14.3%. Wolbachia was not detected in13populations, but six strains of Wolbachia (wChisupl-wChisup6) were identified based on wsp sequences isolated in other10populations (HM165272, HQ336510, HQ336514, HQ336511, HQ336512, HQ336513). Among these strains, wChisup1-wChisup2belong to Group-A and wChisup3-wChisup6belong to Group-B. There is no obvious geographical pattern for the prevalence and distribution of the six Wolbachia strains. Sequence alignment analysis indicates that wsp sequences found in C. suppressalis is high, and these sequences are also closely related to those in other species.2. Infection frequencies of Wolbachia in26geographical populations of C. medinalis range from10.0-90.0%with an average infection rate at58.8%by using wsp, ftsZ and16S rDNA sequences, respectively. Wolbachia was detected in all the geographically separate populations. The Wolbachia detected in different C. medinalis populations are100%identical to each other with its wsp, ftsZ, and16S rDNA sequences, which all belong to Group-B. Sequence alignment analysis indicates that wsp, jisZ and16S rDNA sequences found in C. medinalis are also closely related to those in other species.3. All the mitogenomes of C. suppressalis (15395bp), C. medialis (15388bp), and S. inferens (15413bp) include37genes and an A+T-rich region. The gene order and transcription direction are the same to other lepidopteran species. All the nucleotide compositions show a high bias towards A and T. The number and length of the integenic regions and overlap regions are different, but they all exist three major integenic regions with over30bp and a conserved8-bp overlap region between tRNATrp and IRNA Most protein coding genes (PCGs) of the three mitogenomes start with a typical ATN codon and stop with TAA codon. The average A+T-content of the protein coding genes in S. inferens mitogenome is similar to other two species, so are AT-skews and GC-Skews. However, the position of the highest A+T-content of13PCGs is different among the three mitogenomes.4. All the mitogenomes include22tRNA genes. The anticodons of most tRNAs are GNN and UNN. tRNA genes have the typical cloverleaf secondary structures except for the tRNASer(AGN) gene, which was found with the absence of a DHU arm. Most tRNAs exist mismatched base pairs in which the number of G-U pairs is usually the most. Meanwhile, the secondary structures of lrRNA and srRNA genes in S. inferens are similar to those of other two mitogenomes, in which there are49helices in lrRNA gene and33helices in srRNA gene. The A+T-rich regions of three mitogenomes contain some typical strtuctures:the conserved motif ATAGA(T) followed by a18-22bp poly-T stretch, some tandem reapeted units. Meanwhile, the similar potential stem-loop structure was found in S. inferens and C. medialis mitogenomes. In addition, there is a microsatellite (TA)n in C. medinalis.5. Based on the combined data set of nucleotide and amino acid sequences of13protein coding genes, the phylogenetic relationships of36lepidopteran species was reconstructed using different methods. The result indicates similar topologies between the maxmium likelihood (ML) and Bayesian inference (BI) methods, and supports that the phylogenetic relationships are very close among Bombycoidea, Geometroidea, Noctuoidea, Pyraloidea, and Papilionoidea. The result basically supports the traditional view.