Four complete mitogenomes of Eysarcoris rosaceus, E. montivagus, E. gibbosus, E. annamita and one near-complete mitochondrial genome of E. ventralis were sequenced and used to explore the phylogenetic relationships of tribes within the subfamily Pentatominae. The mitogenomes range from 15,422 to 16,043 base pairs (bp) in length and encode 37 genes, including 13 protein-coding genes (PCGs), two rRNA genes, 22 tRNA genes (21 in E. ventralis), and a control region. Similar to other heteropteran species, the AT contents of the sequenced species were higher than their GC contents. The most frequently used start/stop codon was ATN/TAA. GTG was only found in atp6 and atp8 of E. gibbosus. All transfer RNA genes (tRNAs) exhibit the typical cloverleaf secondary structure, except for the trnS1 and trnV, which lacks the stem of the DHU arm. The length and copy number of repeat units were conserved within Eysarcoris, with the exception of E. gibbosus. Phylogenetic analyses based on mitogenomes using both maximum likelihood (ML) and Bayesian inference (BI) methods strongly supported the relationship among tribes within Pentatominae and confirmed that Graphosoma should be an intermediate lineage of Pentatominae. The relationship between Eysarcoris and Carbula was strongly supported and combined with our previous geometric morphometrics and chromosomal studies, suggest the Eysarcoris should belong to the tribe Eyasrcorini. This work will help to enhance our understanding of mitochondrial genomic evolution and phylogenetic relationships in Pentatominae.

In pyrrhocorids, digestion of food occurs mainly in the midgut, which is divided into four parts (M1-M4), and takes between three and four days. Food is retained in M1 for about 5 h and passes quickly through M4. However, food is retained in M2 and M3 much longer, about 70 to 90 h. The different stages in digestion may be influenced by different microbial populations in the different parts of the midgut. In the present study, the microbiota in the four parts of the midgut of Pyrrhocoris sibiricus were analysed in detail using high-throughput sequencing of the 16S rRNA V3-V4 region. The most abundant bacteria in M3 were Actinobacteria (Coriobacteriaceae) whereas it was Proteobacteria (gammaproteobacteria) in M1, M2 and M4. Actinobacteria was the second most abundant bacterial group in M2. According to the PCA analysis, M2 and M3 have the most similar bacterial communities. Burkholderia, which is closely related to the plant-associated beneficial and environmental (PBE) group, was also found in M1, M2 and M4. Predictive functional profiles of the metagenomes revealed that metabolism mostly occurred in M2 and M3. The PICRUSt results were consistent with the 16S rRNA metagenomic analysis and indicate that the bacteria in M2 and M3 play an important role in degrading complex dietary components.