The karyotype of Armenian populations of the black fly Prosimulium petrosum Rubtsov, 1955 was characterized and compared with that of all other chromosomally known Palearctic members of the Prosimulium hirtipes group. Analysis of the polytene chromosomes established that Prosimulium petrosum is most closely related to European populations of Prosimulium latimucro (Enderlein, 1925) with which it shares an identical fixed chromosomal banding sequence. Its validity as a species, separate from Prosimulium latimucro, is based on its unique sex-differential sections in the expanded centromere region of chromosome I, in agreement with the unique structural configuration of the hypostomal teeth of its larvae. Prosimulium petrosum and Prosimulium latimucro, therefore, are homosequential species, demonstrating the value of a combined chromosomal and morphological approach in determining species status.
Keywords: Black flies; chromosomal inversions; homosequential species; polytene chromosomes; sex chromosomes.