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The karyotype of Camptochironomus pallidivittatus Edwards, 1929 (Diptera, Chironomidae) from five populations of the Lower Volga region and Central Caucasus (the northern macroslope) has been studied. In populations of S. pallidivittatus from the Central Caucasus, 11 banding sequences (BS) were found; one sequence, pal B10, was new to the species. In the Saratov population, 11 BS were also found, three of which were new for the species-pal A3, pal B11, and pal B12. The banding sequences detected for the first time have not yet been found in other parts of the habitat of this species and may be endemic to these regions. In the studied populations ofS. pallidivittatus, banding sequences were found that were nonstandard but fixed in the karyotype. This is indicative of some degree of chromosomal divergence. These banding sequences include pal A2.2 in arm A and pal B10.10 in arm B in the Central Caucasus region, as well as pal B2.2 and pal G2.2 in the Lower Volga region. Arms A, B, D, and G in the Central Caucasian populations and A, B, and D in the Saratov oblast were polymorphic. The composition of heterozygous sequences between populations from different regions coincided only in arm D (pal D 1.2). In arms A and B, the set of heterozygous BS was different: pal A1.2 and pal B1.10 sequences were found in the Central Caucasian populations, and pal A1.3 and B11.12 were found in Saratov oblast. The number of genotypic combinations of S. pallidivittatus was higher in the Central Caucasus region, whereas the number of zygotic combinations was higher in the Saratov population. The percentage of heterozygous larvae in the Central Caucasian populations varied from 20 to 80, whereas all individuals in the Saratov population had heterozygous inversions. Zygotic combinations of larvae in all the studied populations were different.

The karyotype of Camptochironomus tentans (Fabricius), 1805 (Diptera, Chironomidae) from the populations of the Lower Volga region and Central Caucasus (the northern macroslope) has been studied. In the karyotype of C. tentans from Saratov oblast, 14 banding sequences (BS), 13 genotypic combinations, and 14 zygotic combinations were identified. Four new BSs were described: ten B12, ten F4, ten F5, and ten G4, which are distinguished by simple paracentric inversions from those already known for the species. The chromosomal polymorphism belongs to the inversion type; its level in the Saratov population is generally the same as in populations of other parts of the habitat. The number of heterozygous inversions per specimen was 1.3; the number of heterozygous inversions per arm was 0.86; the percentage of heterozygous larvae was 84.5. The polymorphic arms in C. tentans were A, B, C, and F. Nine previously known BS were revealed in the karyotype of C. tentans from Central Caucasus, and no new sequences were found. Arm B in C. tentans was polymorphic. The zygotic combinations in all the studied populations were distinct.

Karyotypes of the Chironomus nuditarsis Str. (Chironomidae, Diptera) (Keyl, 1962) chironomids from central Caucasian populations located at different altitudes above the sea level (a.s.l.) were examined. Specific features of the inversion polymorphism of the high-mountain (more than 1000 m a.s.l.), foothill (500-1000 m a.s.l.), and plain (up to 500 m a.s.l.) populations were identified. A new chromosome banding sequence, ndt F2 (lg-e 7a-8c), which was endemic to Caucasian populations, was described. With the increase in the altitude of the reservoir a.s.l., the decrease in the frequency ofndt G1.2 and ndt B2.2 inversions and the number of inversions per individual and per arm was observed. In the high-mountain population, only the ndt G2.2 homozygotes were detected. The plain population is an interstitial population, while foothill and high-mountain populations are terminal. Cytogenetic distances between the high-mountain and other samples range from 0.174 to 0.223, which is higher than the mean interpopulation value for this species (0.138). The allochrony of the life cycle in aborigines from the foothill population and aborigines from the high-mountain population can be caused by factors such as low high-mountain reservoir temperature. This factor increases the duration of the stages of larvae developmental, which leads to a reduced number of generations and results in a shift in the imago flight and mating timing.

This is the first study to infer the phylogenetic structure of minges of the subfamily Chironominae from the amino acid sequence of cytochrome oxidase I (COI). The subdivision of Chironominae into two tribes, Chironomini and Tanytarsini, has been confirmed. The segregation of the genera Pseudochironomus and Riethia into a separate tribe has not been confirmed. Stenochironomus gibbus forms a branch considerably deviating from the subfamily Chironominae. The genus Micropsectra is formed by a large polyphyletic cluster that also includes the genera Virgotanytharsus, Reotanytharsus, Kenopsectra, and Parapsectra. Tanytarsus is the basal genus of the tribe Tanytarsini. The times of divergence of the main taxa of Chironominae have been estimated. The calculated time of divergence of the genus Chironomus disproves the assumption that it is phylogenetically old.

The sequence of a 595-bp fragment of the mitochondrial COI gene was determined for the species Chironomus usenicus and Chironomus curabilis of the genus Chironomus. Phylogenetic reconstructions based on the analysis of the COI gene sequence coincide on the whole with cytogenetic data, permitting Ch. usenicus and Ch. curabilis to be regarded as members of the group plumosus. Chironomus usenicus and Ch. plumosus have identical COI gene sequences. Two hypotheses explaining this identity are considered: inheritance of mtDNA from one of the parental species during hybridogenesis and horizontal transfer of mitochondrial genes.

Hybridogenesis as a possible way of speciation in Chironomidae was considered with special reference to the species Chironomus usenicus resulting from hybridization between C. plumosus and C. behningi. The three species had 2n = 8 and belonged to the thummi cytocomplex with chromosome arm combinations AB, CD, EF, and G. Arm G had a marker chromosome disk sequence (CDS) and was used to demonstrate the hybrid origin of C. usenicus. Most C. usenicus larvae were heterozygous in CDS of arm G. CDS use G2 proved to be identical to CDS beh G1 of C. behningi and CDS use G1, to CDS plu G1 of C. plumosus. It was assumed that C. usenicus results from hybridization between eurybiont C. plumosus and stenobiont C. behnigni at the boundary of their species areas, in freshwater or brackish water bodies of the southern Saratov oblast and northern Kazakhstan. Morphologically and karyotypically, the hybrid was probably similar to C. plumosus. Crosses with C. plumosus eliminated virtually all C. behningi chromosome sequences from the karyotype of the hybrid. Further chromosome divergence resulting in C. usenicus involved a number of chromosome rearrangements, including duplication of pericentric heterochromatin and other chromosome regions; inversion, which occurred in arm F (regions 13-16) and was fixed in the karyotype; and other paracentric inversions and deletions accumulated in heterozygote in the karyotype pool of the species. Since C. behningi was eliminated from the introgression zone and its species are reduced, the assimilation character was assumed for introgressive hybridization of C. behningi and C. plumosus.