The Complete Mitochondrial Genome Analysis And Part Of Moths DNA Barcoding In Lepidoptera

The mitochondrial genome is widely used for population genetic structure, gene flow, phylogeography and phylogenetic study, because of the structural stability, smaller length, less frequent reorganization and generally maternal inheritance. Lepidoptera is classified as Insecta, and widely distributed around the world with approximately250,000species. At present, there are34species mitochondrial genome sequenced successfully in Lepidoptera. But it is still very limited for large Lepidopteran populations. To reveal mitochondrial genome evolution and the phylogenetic relationship of Lepidoptera, it is very necessary that accelerating the Lepidopteran mitochondrial genome sequencing and analysis.We selected two species (rice moth Corcyra cephalonica and leafminer moth Leucoptera malifoliella) to sequence and annotate the complete mitochondrial genome, and conducted a comparative analysis of the mitochondrial genomes in Lepidoptera, which mainly include the characteristics of base composition, codon usage, evolutionary rate of each protein-coding genes. Based on the mitochondrial genome we reconstructed phylogenetic relationship of Lepidoptera.Lepidopteran moths mostly are agricultural and forestry pests, and mainly feeding on host plant during the larval stage. The DNA barcode database can ensure fast and accurate identification of moths’caterpillars, and provide accurate information for pest control. Based on mitochondrial coxl gene we surveyed and identified lepidopteran moths collected from an orchard, tested the successful rate of BOLD system and NJ tree for lepidopteran pests, calculated and discussed the inter-and intra-specific genetic distances.The main results are as follows:1. Nucleotide composition of C. cephalonica and L. malifoliella mitogenome genome are highly A+T biased (80.43%) and (82.57%),like other insects. Twelve PCGs start with a typical ATN codon, with the exception of cox1gene, which uses CGA as the initial codon.22tRNA genes evidence cloverleaf secondary structure, but trnS1(AGN) is found to lack the DHU stem. The secondary structure of rrnL and rrnS are generally similar to other lepidopterans with some minor differences. The L. malifoliella A+T-rich region includes the motif ATAGA, but the poly (T) stretch is replaced by a stem-loop structure, which may have a similar function to the poly (T) stretch. There is a high sequence identity between the intergenic spacer sequence trnQ-nad2and the neighboring nad2from most lepidopteran insects, this indicated that the intergenic spacer sequence trnQ-nad2may have originated from a partial duplication of the nad2gene.2. The Lepidopteran mitochondrial genome have higher AT content, the AT skew and GC skew on the H chain of protein coding region are negative, which indicating that the T content is higher than A, the C content higher than G. Based on the Ka/Ks ratio, the interspecific gene loci divergence and gene mutation analysis, we found that evolutionary rate of dehydrogenase subunit the NADH gene usually faster than cytochrome oxidase gene. The coxl gene is moderate compared to other genes, and suitable for DNA barcode study.3. The basic structure of the phylogenetic tree based the mitochondrial genomes is (Yponomeutoidea+(Tortricoidea+(Papilionoidea+(Pyraloidea+(Noctuoidea+(Geometroidea+Bombycoidea)))))). The positions of Papilionoidea, Pyraloidea and Noctuoidea are different from the traditional classification. The position of Yponomeutoidea represented by L.malifoliella, is same as traditional classification. Yponomeutoidea is sister group to the other lepidopteran superfamilies covered in the present study.4. The NJ tree based on coxl gene shows identification successful rate is99.3%for moths collected from orchard, which prove that coxl gene is suitable for identification of Lepidopteran moths. The successful rate of the BOLD system is75.1%, and the the big moths have higher rates than the small moths,which shows the BOLD system lacked datas of small moths. The identification successful rate is94.6%when results similarity is greater than99%in the BOLD system, and successful rate is89.6%when the similarity in the range of98-99%, and successful rate is12.2%when the similarity less than98%. So it is accurate that the similarity of BOLD system identification is greater than99%for common species. Inter-and intra-specific genetic distances show that86%of the intraspecific genetic distances are less than1.0percent,14%are in the range of1.0-4.3percent. The interspecific genetic distances of the same genus are in the range of1.3-15.3percent, there are overlaps between inter-and intra-specific genetic distances, and not threshold value between inter-and intra-specific genetic distances.