Drosophilidae
D. melanogaster is not so much studied in the field as in the laboratory. The best-known studies of Drosophila in a natural environment was done by Dobzhansky and colleagues on Drosophila pseudoobscura from the early 1930s to  1970. Reprints and discussions are in Lewontin et al 2003, and theoretical discussions in Dobzhansky, 1970.