Complete mitochondrial genomes of Bittacus strigosus and Panorpa debilis and genomic comparisons of Mecoptera.

Mitochondrial genomes play a significant role in reconstructing phylogenetic relationships and revealing molecular evolution of insects. However, only four mitochondrial genomes were reported in Mecoptera to date. Here, we obtained two new complete mitochondrial genomes of the hangingfly Bittacus strigosus Hagen, 1861 and the scorpionfly Panorpa debilis Westwood, 1846. The results show that the complete mitogenome sequences of B. strigosus and P. debilis are 15,825 and 17,018 bp, respectively, both containing 37 genes and one control region. The mecopteran mitogenomes are highly similar in A + T bias, AT-skew, and GC-skew. Tandem repeats of the control region were discovered in Mecoptera for the first time. The sliding window, genetic distance, and Ka/Ks ratio analyses indicate the purifying selection of 13 protein-coding genes, the lowest evolutionary rate of cox1, and the highest sequence variability of atp8. Considering the sufficiently large size, fast evolution, and high ratio of Ka/Ks, nad4L and nad6 are regarded as potential markers for future phylogenetic analyses, population genetics, and species delimitations in Mecoptera. The phylogenetic relationships were reconstructed for four families of Mecoptera based on all six available mitogenomes using Bayesian inference and maximum likelihood methods. The phylogeny is presented as Boreidae + (Nannochoristidae + (Bittacidae + Panorpidae)).