Complete sequence determination and analysis of mitochondrial genome of Illeis bistigmosa

【Objective】 The purpose of the study was to characterize the complete mitochondrial genome structure of Illeis bistigmosa(Mulsant, 1850) at the level of the mitochondrial genome, to analyze its classification status within Coccinellidae, and to provide a theoretical basis for revealing the phylogenetic and evolutionary relationships of Coccinellidae insects.【Method】 The mitochondrial genome of I. bistigmosa was sequenced by using Illumina Next-generation sequencing technique, and the genome sequence was assembled and annotated to analyze its structural features and base composition. The phylogenetic trees of mitochondrial genomes of 16 Coccinellidae species were constructed by using maximum likelihood and Bayesian methods to analyze their phylogenetic relationships within Coccinellidae.【Result】 The mitochondrial genome sequence of I. bistigmosa was 17840 bp in length, including 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and 1 A+T rich region. The AT content in the whole genome sequence was 78.44%, showing significant A+ T bias. Among the 13 protein-coding genes, 12 genes used ATN as the start codon, except for the cox1 gene, which had TTG as the start gene. The termination codon of nad4, nad5, cox2, and cox3 genes ended in a separate T. Except for trnS1 and trnP genes, all the remaining 20 tRNAs had the typical clover-leaf-like structure with U-U or U-G base mismatched in the secondary structure. Pgylogenetic analysis showed that all species of Coccinellinae clustered in the same branch, confirming Coccinellinae to be a monophyly. I. bistigmosa grouped with two other species of Illeis(I. koebelei and I. cincta) in a branch, forming a sister relationship.【Conclusion】 In this study, the mitochondrial genome complete sequence of I. bistigmosa is obtained. The mitochondrial genome of I. bistigmosa conforms to the general characteristics of Coccinellidae mitochondrial genome. I. bistigmosa is closely related to I. koebelei and I. cincta, which is in accordance with the traditional morphological classification.