Morphometric variation of the face fly, Musca autumnalis DeGeer, in the United States
The face fly, Husca autumnalis DeGeer, has recently expanded into the United States from what seems to be a single, genetically depauperate, introduction. In order to study the effects of natural selection and genetic drift on this newly arrived species, specimens were collected from localities throughout the 1971 distribution of the face fly. A detailed study of the morphology of the face fly has revealed significant differences among its populations. Utilizing univariate and multivariate statistical procedures, the geographic morphometric variation of the face fly has been described and related to putative environmental causes. Evidence for natural selection is strong, indicating possible winter and spring selection on adult females and winter and summer selection on adult males. Genetic drift may be affecting some of the characters of the face fly, but the evidence is not strong.