Scelimeninae is a key member of the pygmy grasshopper community, and an important ecological indicator. No mitochondrial genomes of Scelimeninae have been reported to date, and the monophyly of Scelimeninae and its phylogenetic relationship within Tetrigidae is still unclear. We sequenced and analyzed eight nearly complete mitochondrial genomes representing eight genera of Scelimeninae. These mitogenomes ranged in size from 13,112 to 16,380 bp and the order of tRNA genes between COII and ATP8 was reversed compared with the ancestral order of insects. The protein-coding genes (PCGs) of tetrigid species mainly with the typical ATN codons and most terminated with complete (TAA or TAG) stop codons. Analyses of pairwise genetic distances showed that ATP8 was the least conserved gene within Tetrigidae, while COI was the most conserved. The longest intergenic spacer (IGS) region in the mitogenomes was always found between tRNA^Ser(UCN) and ND1. Additionally, tandem repeat units were identified in the longest IGS of three mitogenomes. Maximum likelihood (ML) and Bayesian Inference (BI) analyses based on the two datasets supported the monophyly of Tetriginae. Scelimeninae was classified as a non-monophyletic subfamily.

The nearly complete mitochondrial genome (mitogenome) of Teredorus nigropennis was determined and analyzed. This mitogenome was 14,652 bp in size and encoded 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes. The most common start codon is ATN, the most common termination codon is TAA and two genes have incomplete termination codon T (TA). The overall nucleotide composition was 45.2% of A, 10.2% of G, 28.6% of T, and 16.1% of C. The data will increase the basic information of Tetrigidae phylogenetic research and can help to better understand the phylogenetic status of T. nigropennis in Tetrigiodea.

Mayflies of the family Neoephemeridae are widespread in the Holarctic and Oriental regions, and its phylogenetic position is still unstable in the group Furcatergalia (mayflies with fringed gills). In the present study, we determined the complete mitogenomes of two species, namely Potamanthellus edmundsi and Pulchephemera projecta, of this family. The lengths of two mitogenomes were 15,274 bp and 16,031 bp with an A + T content of 73.38% and 73.07%, respectively. Two neoephemerid mitogenomes had a similar gene size, base composition, and codon usage of protein-coding genes (PCGs), and the sequenced gene arrangements were consistent with the putative ancestral insect mitogenomes as understood today. The most variable gene of Furcatergalia mitogenomes was ND2, while the most conserved gene was COI. Meanwhile, the analysis of selection pressures showed that ND6 and ATP8 exhibited a relaxed purifying selection, and COI was under the strongest purifying selection. Phylogenetic trees reconstructed based on two concatenated nucleotide datasets using both maximum likelihood (ML) and Bayesian inference (BI) estimations yielded robust identical topologies. These results corroborated the monophyly of seven studied families and supported the family Leptophlebiidae as being of the basal lineage of Furcatergalia. Additionally, the sister-group relationship of Caenidae and Neoephemeridae was well supported. Methodologically, our present study provides a general reference for future phylogenetic studies of Ephemeroptera at the mitogenome level.

Epeorus Eaton, 1881 is a diverse mayfly genus in Heptageniidae comprising more than 100 species which are further divided into nine subgenera and several species groups. However, the classification and the phylogenetic relationships among them are still uncertain. Here, 15 complete mitochondrial genomes of Epeorus were sequenced and compared together with six available ones of same genus in the NCBI database. Based on morphological classification, the 21 mitogenomes were classified into six subgenera (Proepeorus, Epeorus s.str., Belovius, Iron, Caucasiron and Siniron) and four species groups (G1, G2, montanus and longimanus). Among all analyzed mitogenomes, the gene rearrangement of trnI-trnM-trnQ-NCR-ND2 was first found occurring in three species of group G1, whereas the gene block trnI-trnM-trnQ-trnM-ND2 was observed in all other mitogenomes of Epeorus. Furthermore, the genetic composition and codon usage of species in group G1 were also significantly different from all other Epeorus species, except group longimanus. The intergenic spacer between trnA and trnR, which has the stem-loop secondary structure, occurred in all 21 mitogenomes, and the sequences of stems and loops were conserved within species groups. Furthermore, the phylogenetic analyses strongly support the monophyly of all species groups, although three of six recognized subgenera Proepeorus, Belovius, and Iron, were shown as the non-monophyletic groups.

The pygmy grasshoppers, which belong to the superfamily Tetrigoidea, exhibit remarkable environmental adaptability. However, no study has yet reported a reference genome for this group. In this study, we assembled a high-quality chromosome-scale genome of Eucriotettix oculatus, which survive in the environment heavily polluted by heavy metals, achieved through Illumina and PacBio sequencing, alongside chromosome conformation capture techniques. The resulting genome spans 985.45 Mb across seven chromosomes (range: 71.55 to 266.65 Mb) and features an N50 length of 123.82 Mb. Chr5 is considered to be the single sex chromosome (X). This genome is composed of 46.42% repetitive elements and contains 14,906 predicted protein-coding genes, 91.63% of which are functionally annotated. Decoding the E. oculatus genome not only promotes future studies on environmental adaptation for the pygmy grasshopper, but also provides valuable resources for in-depth investigation on phylogeny, evolution, and behavior of Orthoptera.