Assaying the usefulness of mitochondrial sequences of the class Hexapoda for DNA barcode

DNA barcode projects for the superclass Hexapoda have been initialized and are progressing, accumulating large numbers of mitochondrial gene sequences. However, due to the large amount of data, overviews of the DNA barcode projects for Hexapoda have not been reviewed, until now. Here, we report the current status of the DNA barcode projects with the aid of the Insect Mitochondrial Genome Database (IMGD; http://www.imgd.org/), which contains 128,562 partial mitochondrial gene sequences (PMEs) of Hexapoda. Of the 37 mitochondrial genes, the COI gene has been popularly used for molecular studies (22,379 PMEs; 17.40% out of 128,562 PMEs) in all 33 hexapod orders. In 513 studies, different portions of the COI PMEs were used in different fashions among the hexapod orders. By calculating the genetic divergences of COI PMEs both intra-species and inter-species in 21 hexapod orders, the COI PMEs were distinguished by 5% sequence divergence; some other mitochondrial genes presented higher genetic divergences than that of COI, in certain orders. Based on these results, we confirm that DNA barcodes are a useful tool for identifying hexapod species, and several mitochondrial genes can be good molecular markers to support COI studies.