Abstract
Studies on the biology and control of biting flies in the Canadian north have been described by Hocking et al. (1950), Twinn et al. (1948), and Twinn (1950). The biological investigations have been directed largely toward the economic control of biting flies in isolated military areas. In the subarctic regions of North America so many factors influence the rate of development of mosquitoes that simple relations of time and temperature cannot be used to estimate adequately the periods of infestation. Casual field observations of mosquito larvae and pupae suggested that behaviour patterns peculiar to northern species modify the effect of environmental conditions on the rate of development.