The Diurnal Periodicity of Drosophila Pseudoobscura in Southern California

The advantages of Drosophila which have made it ideal for many kinds of genetic research are combined in Drosophila pseudoobscura with the advantage of an ecology which limits it to areas comparatively undisturbed by man. Dobzhansky has made use of this combination in his extensive studies of the genetics of natural populations. However, the natural history of this species is relatively unknown and apparently quite complex. Difficulties in the interpretation of genetic phenomena therefore arise. Until very recently D. pseudoobscura was known in nature only from adults captured in collecting cups, and even now very little is known about ovipositing, the larval habitat, pupation sites, and breeding habits under natural conditions. The discovery and description of these and other ecological relationships is necessary in order that the genetic phenomena which have been observed can be fully understood. One of these relationships is the diurnal periodicity of locomotor activity which was described by Dobzhansky and Epling (1944). The present paper is concerned with the reaction of adult flies to the major physical factors of the environment, so far as these reactions affect the diurnal periodicity.