Mitochondrial genomes of Sternochetus species (Coleoptera: Curculionidae) and the phylogenetic implications.

The three weevil species, Sternochetus gravis, S. mangiferae, and S. olivieri, have all been reported to be serious pests of mango fruits. Morphology, biology, and various management approaches of these economically important weevils have been well studied. However, no mitochondrial genomes have been reported from the genus Sternochetus. Herein, we assembled mitogenomes of all the three Sternochetus species to reveal their mitogenomic characteristics. A DNA library of 350 bp insert size was constructed and sequenced in Illumina's HiSeq 6000 platform with a pair-end 150 bp sequencing strategy by Novogene. The sequence reads were assembled using GetOrganelle v1.7.1 and the genes were annotated by Geneious Prime 2021.0.3 and MITOS Web Server. Coupled with 61 published mitogenomes from 13 subfamilies of Curculionidae, we reconstructed phylogenetic trees to resolve evolutionary relationships of these closely related species and also examined subfamily-level classification among Curculionidae. All three mitogenomes are double-stranded circular molecules with 22 transfer RNA genes, 13 protein-coding genes (PCGs), 2 ribosomal RNA genes, and 1 noncoding control region as in other insects. Higher interspecific nucleotide divergence (about 10%) of 13 PCGs indicated these three Sternochetus species diverged a long time ago. Phylogenetic analyses using both maximum likelihood and Bayesian inference methods showed that Sternochetus falls into the basal clade of Cryptorhynchini, a tribe in the subfamily Molytinae. The relationship of S. olivieri as a sister species to S. gravis + S. mangiferae was strongly supported. The monophyly of Cryptorhynchini was also well supported whereas Molytinae was suggested to be a polyphyletic group.