Species Chironomus sp. prope agilis Kiknadze, Siirin, Filippova et al., 1991 belongs to the Ch. plumosus group of sibling species. It was described on the basis of its karyotype and analysis of isozymes from one population in the Urals but since then no quantitative data on chromosomal polymorphism of this species have been published. The goal of this study is to broaden our knowledge of the chromosomal polymorphism and distribution of the Chironomus sp. prope agilis, which, along with the data on chromosomal polymorphism of other species from the Ch. plumosus group, can give us a better understanding of the connection between chromosomal polymorphism and ecological conditions of habitats. The specimens of Chironomus sp. prope agilis were found only in 8 natural populations from the Urals, Western Siberia and Kazakhstan, which allows us to conclude that the species range of Chironomus sp. prope agilis is not as wide as for most other species from Ch. plumosus group. An analysis of chromosomal polymorphism in these 8 natural populations of Chironomus sp. prope agilis has been performed. All of the studied populations were either monomorphic or showed very low level of chromosomal polymorphism, with 4.4–8.7% of heterozygous specimens per population and 0.04–0.08 heterozygotic inversion per larvae. The total number of banding sequences found in the banding sequence pool of Chironomus sp. prope agilis is 10. The mapping of banding sequence p’ag2B3 is presented for the first time. Besides inversions, one reciprocal translocation was found in a population from Kazakhstan, B-chromosome was found in one population from the Urals region of Russia, and heterozygosity of the level of expression of Balbiany rings in arm G was observed in several studied populations.
