FREQUENCY CHANGES OF B-CHROMOSOME IN SYNA NTHROPIC SPECIES OF BLOODSUCKING BLACKFLIES (DIPTERA, SIMULIIDAE)

B chromosomes were found in populations of synanthropic blackflies Cne tha zakhariensis and Tetisimulium condici (26.8 and 39.6% of individua ls, respectively) inhabiting reservoirs influenced by human factors. T he populations of C. zakhariensis, over 20 years of existence in the s ame biotype, revealed an increase of 2.9 times of individuals with B c hromosomes. This increase might be associated with increased human inf luence. Only one parameter of 13 analyzed manifested a phenotypic effe ct associated with the presence of B chromosomes: the number of bristl es in the large larval fan decreased with the appearance of B chromoso mes.