In the body of literature which deals with flies of the genus Drosophila, there is an increasingly large and significant segment which is concerned with the genetics of natural populations and in which special attention has been given to the study of problems of speciation and microevolution. Purposely chosen for much of this type of work have been those species of the genus which appear to be ecologically the least affected by the activities of man and which are generally considered non-domestic or 1 species. Thus, in the western United States, attention has been centered on such wild species as Drosophila pseudoobscura and its relatives (e.g., Dobzhansky and Epling 1944), whereas in the eastern and south-central parts of the country such forms as D. algonquin (Miller 1939), the americana-texananovamexicana complex (Hsu 1950) and D. robusta (e.g., Carson and Stalker 1947) have been used. In contradistinction to the clearly domestic species, which are mostly cosmopolitan in distribution (e.g., D. melanogaster, D. hydei, D. immigrans, D. busckii and others), the so-called wild species are most readily trapped in relatively undisturbed woodland habitats and have discontinuous and natural distributions. These species, furthermore are only rarely bred from garbage, rotting fruits, vegetables and similar potential breeding sites associated with the activities of man. This does not mean that the distribution of wild species is totally unaffected by human activities because, with some exceptions, the members of the genus are generally adaptable and will be attracted to, and feed upon, any carbohydrate source which permits the growth of