[Molecular criteria in insects systematics: bar-coding gene COI range of variability as a taxonomic criterion for genus, tribe, and subfamily, with Chironominae and Orthocladiinae midges (Chironomidae, Diptera) as a case study].

Contemporary systematics of insects is based mainly on morphological traits. However, their usage is limited both by high variability and complications in comparisons of remote taxa due to low number of common traits. In whole, this leads to a somewhat subjective view when elaborating the system. Unlike morphological ones, molecular traits of taxa, revealed by use of marker genes such as gene cytochrome-c-oxidase I (COI), are less variable and more uniform, which allows them to be used as a criterion of genus, tribe, and subfamily for a wide range of organisms. Application of molecular criteria appears to be all the more important when constructing the system for groups of organisms with high morphological and specific diversity, such as midges (Chironomidae, Diptera). Last years, the DNA-sequence of gene COI is becoming widely used for species identification as a bar-coding one. Its use as a criterion for taxa of super-species level is hampered by its high nucleotide variability. We established the bounds of COI nucleotide and aminoacid divergence between midge species of Chironominae subfamily belonging to the same genus, same tribe, different tribes, as well as between species of Chironominae and Orthocladiinae subfamilies. It is shown that the level of aminoacid divergence reflects molecular boundaries of genus and tribe better than nucleotide one. It can be stated that if the level of aminoacid divergence falls within the limits from 0 to 1.7% then a pair of species compared belongs to the same genus; if it falls within the limits from 1.7 to 4.0% then they belong to the same tribe; within the limits from 4.6 to 6.3%--to different tribes; if it exceeds 7.9%--to different subfamilies. The accuracy of identification when using these ranges turns out to be not less than 75%. In this regard, bounds of COI sequence aminoacid divergence may be used as taxonomic criteria for midge genus, tribe or subfamily.