Abstract: The superorder Psocodea has over 10 000 described species in two orders: Psocoptera (barklice and booklice) and Phthiraptera (chewing lice and sucking lice). Many psocodean insects are important storedproduct pests, and some are important vectors for human and animal diseases. Recent studies indicate that psocodean insects have the most dramatic variation of mitochondrial (mt) genomes observed in insects, including genome architecture, gene order, gene content and gene strand asymmetry. In this review, we summarized the evolutionary features of the multipartite mt genomes observed in species of the Psocodea and introduced a new concept “mitochondrial genome karyotypes” to describe the complexity of animal mt genome. Furthermore, in combination with fragmented mt genomes of other bilateral animals, we proposed the mechanism to explain how multipartite circular mt genomes are generated. We propose that the selection pressure for compact mt genomes in bilateral animals favors small mt chromosomes when small mt chromosomes co-exist with the typical large mt chromosomes. Thus, small mt chromosomes may have selective advantages over large ones in bilateral animals. Fragmentation of mt genome is likely an important strategy to streamline mt genome. Meanwhile, we also investigated the current controversial views on the phylogenetic relationships among major lineages of the Psocodea. This review will provide new insights into the evolutionary pattern of mt genome of psocodean insects and other bilateral animals, as well as the phylogeny of Psocodea.

Key words: Psocoptera, Phthiraptera, booklice, mitochondrial genome, gene rearrangement, multipartite genome, phylogeny