Colonization of North America by the European Species, Drosophila subobscura and D. ambigua

Abstract
Two European species, Drosophila subobscura and D. ambigua, have been found in the Pacific Northwest. Drosophila subobscura occurs from central California, N to southwestern British Columbia. Drosophila ambigua has been found only in the southwestern mainland of British Columbia. These species can be distinguished from the endemic obscura-subgroup species, D. pseudoobscura, D. persimilis and D. miranda, by sex comb, vaginal plate and wing bristle morphology, by allozymic differences and by differences in the polytene chromosomes.