The sister relationship between Trichoptera and Lepidoptera has often been supported in a diverse study, but mitochondrial genomes (mitogenomes) based lepidopteran phylogenetic studies have never utilized Trichoptera as outgroup mainly due to unavailability. Therefore, the effect of alternatives that were previously used (e.g., Diptera, Hymenoptera, and Orthoptera) or Trichoptera as outgroups on the lepidopteran phylogeny remained unknown. In this study, we sequenced three complete mitogenomes of Trichoptera belonging to two suborders and characterized the genomic features of Trichoptera and tested the outgroup effect for lepidopteran phylogeny. The 15,208 ~ 15,285-bp long caddisfly mitogenomes harbor gene content typical of the animal mitogenomes. The orientation and gene order of the three species belonging to the suborder Integripalpia was identical to that of the most common type that has been hypothesized as ancestral for insects, but Cheumatopsyche brevilineata belonging to another suborder Annulipalpia has rearranged QIM, all encoded in forward direction between the A+T-rich region and ND2, instead of the ancestral IQM, with Q inverted. Further, the annulipalpian species had a typical start codon ATG, instead of CGA that are commonly found in other trichopteran species and majority of Lepidoptera. Phylogenetic analysis with different outgroups (Diptera, Hymenoptera, and Orthoptera, Coleoptera, and Trichoptera) and 115 lepidopteran mitogenomes has shown insensitivity either with Trichoptera, Diptera, or Coleoptera, but artificial grouping and lowered nodal support were found with Hymenoptera. The Trichoptera-based consensus topology were: (((((((Bombycoidea + Noctuoidea) + Pyraloidea) + Papilionoidea) + Cossoidea) + Tortricoidea) + Yponomeutoidea) + Hepialoidea).

• Min Jee Kim(Department of Applied Biology, Chonnam National University)
• Iksoo Kim(Department of Applied Biology, Chonnam National University)