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Mitochondrial genomes have been widely used for phylogenetic reconstruction and evolutionary analysis in various groups of Insecta. Gene rearrangements in the mitogenome can be informative characters for phylogenetic reconstruction and adaptive evolution.Trichoptera is one of the most important groups of aquatic insects. Prior to this study, complete mitogenomes from Trichoptera were restricted to eight families, resulting in a biased view of their mitogenome structure and evolution. Here, we assemble new mitogenomes for 66 species by high-throughput sequencing. The mitogenomes of 19 families and 47 genera are documented for the first time. Combined with 16 previously published mitogenomes of Trichoptera, we find 14 kinds of gene rearrangement patterns novel for Trichoptera, including rearrangement of protein-coding genes, tRNAs and control regions. Simultaneously, we provide evidence for the occurrence of tandem duplication and non-random loss events in the mitogenomes of three families. Phylogenetic analyses show that Hydroptilidae was recovered as a sister group to Annulipalpia. The increased nucleotide substitution rate and adaptive evolution may have affected the mitochondrial gene rearrangements in Trichoptera. Our study offers new insights into the mechanisms and patterns of mitogenome rearrangements in Insecta at large and into the usefulness of mitogenomic gene order as a phylogenetic marker within Trichoptera.

Gene rearrangement of the mitochondrial genome of insects, especially the rearrangement of protein-coding genes, has long been a hot topic for entomologists. Although mitochondrial gene rearrangement is common within Annulipalpia, protein-coding gene rearrangement is relatively rare. As the largest family in Annulipalpia, the available mitogenomes from Hydropsychidae Curtis, 1835 are scarce, and thus restrict our interpretation of the mitogenome characteristic. In this study, we obtained 19 novel mitogenomes of Hydropsychidae, of which the mitogenomes of the genus Arctopsyche are published for the first time. Coupled with published hydropsychid mitogenome, we analyzed the nucleotide composition evolutionary rates and gene rearrangements of the mitogenomes among subfamilies. As a result, we found two novel gene rearrangement patterns within Hydropsychidae, including rearrangement of protein-coding genes. Meanwhile, our results consider that the protein-coding gene arrangement of Potamyia can be interpreted by the tandem duplication/random loss (TDRL) model. In addition, the phylogenetic relationships within Hydropsychidae constructed by two strategies (Bayesian inference and maximum likelihood) strongly support the monophyly of Arctopscychinae, Diplectroninae, Hydropsychinae, and Macronematinae. Our study provides new insights into the mechanisms and patterns of mitogenome rearrangements in Hydropsychidae.

Trichoptera is a highly adapted group of freshwater insects. They are generally more sensitive to dissolved oxygen and water quality than most freshwater organisms, and this sensitivity allows them to be used as reliable biological indicators of water quality. At present, there exists no chromosome-level genome of a hydropsychid species. Cheumatopsyche charites Malicky & Chantaramongkol, 1997 can successfully survive and thrive in polluted streams where other caddisflies are infrequent, suggesting that they are tolerant to latent contamination. Here we report a high-quality chromosome-level genome assembly of C. charites generated combining PacBio long reads and Hi-C reads. We obtained a genome assembly of 223.23 Mb, containing 68 scaffolds with an N50 length of 13.97 Mb, and 155 contigs (99.67%) anchored into 16 pseudochromosomes. We identified 36.12 Mb (16.18%) of the genome as being composed of repetitive elements, identified 369 noncoding RNAs, and predicted 8,772 protein-coding genes (96.80% BUSCO completeness). Gene family evolution analyses identified 7,148 gene families, of which 41 experienced rapid evolution. The expanded gene families were shown to be involved in detoxification metabolism, digestive absorption, and resistance to viruses or bacteria. This high-quality genome provides a valuable genomic basis for the study of trichopteran evolution.