The order Hymenoptera is one of the most species-rich insect orders, with more than 150,000 described extant species. Many hymenopteran insects have very different mitochondrial genome (mitogenome) organizations compared to the putative ancestral organization of insects. In this study, we sequenced 18 mitogenomes of representatives in the order Hymenoptera to increase taxonomic sampling. A total of 475 species were used in phylogenetic analyses, including 18 new mitogenomes and 457 existing mitogenomes. Using a site-heterogeneous model, Bayesian's inference from amino acid data yielded more resolved relationships among Hymenoptera than maximum-likelihood analysis and coalescent-based species analyses. The monophyly of Symphyta was not supported. The Xyeloidea was the earliest branching clade in the Hymenoptera. The Orussoidea was closely related to Apocrita. Within Apocrita, the Parasitoida was non-monophyletic. The monophyly of most Parasitoida superfamilies received strong support. The Proctotrupomorpha clade was supported in Bayesian's analysis. The Apoidea was monophyletic when excluding Ampulex compressa from consideration. The superfamilies Vespoidea and Chrysidoidea were found to be non-monophyletic. Comparisons of mitochondrial gene order revealed a higher frequency of gene rearrangement among lineages with a parasitoid lifestyle, particularly prominent in Chalcidoidea. The degree of gene rearrangement ranked second in specific taxa of Cynipoidea and Ichneumonoidea.
Keywords: Hymenoptera; gene order; mitogenome; phylogenetics; rearrangement.