Effect of environmental pollution on the chromosomal variability of Chironomus riparius Meigen 1804 (Diptera, Chironomidae) larvae from two Piedmont stations

Different frequencies of chromosomal alterations in salivary gland polytene chromosomes AB, CD and EF were described in larvae of Chironomus riparius (syn. Chironomus thummi) from the trace metal-polluted station of Santena o n the river Banna, near Turin, and from the unpolluted station of Corio (40 Km from Turin) which was taken as a reference area. In a sample of 56 larv ae from Santena, no specimen with the standard karyotype in all cells of th e salivary glands was found. Different types of aberrations were found: 33 paracentric and five pericentric inversions, three deficiencies, four ampli fied sections and one chromatid break. Fifteen out of the 38 inversions and two amplified sections appeared to be inherited, while all the other aberr ations were somatic. Most of the aberrations' breakpoints were located on b oth sides of the centromere regions, where constitutive heterochromatin is present. Also functional alterations were observed (mainly telomere and cen tromere decondensations and nine novel puffs). In a sample of 49 larvae of a population from the well-preserved area of Corio only six somatic and one inherited paracentric inversions were found. These results suggest that th e strong destabilization of the genomes of C. riparius larvae from Santena could be a reaction to the activity of the toxic substances present in the polluted sediments of the river Banna.