SOMATIC METAPHASE CHROMOSOMES IN GEOGRAPHIC ISOLATES OF THE CARROT RUST FLY, CHAMAEPSILA ROSAE (F.) (DIPTERA: PSILIDAE)
A comparative study of somatic metaphase complements of the carrot rust fly, Chamaepsila rosae (F.), from England, Prince Edward Island, Ontario, and British Columbia showed that the chromosome number is eight and that all chromosomes are metacentric. The means of the total complement length ranged from 50.8 to 53.5 and the lengths for chromosomal pairs I–IV averaged 36.5, 24.8, 22.3, and 16.5% of the total length respectively for the four regions. The sex chromosomes are the largest elements in the complement, the X chromosome being 36.5% of the total length and the Y 28.8%. The arm ratios for members X, Y, II, III, and IV are 1.34, 1.13, 1.57, 1.21, and 1.34 respectively. Secondary constrictions were both infrequent and irregular in location. The work emphasizes that much caution is necessary in analyzing metaphase chromosomes for taxonomic purposes.