This paper presents a method for clarifying the relationships between development rate curves and temperature regimes in affecting development accumulation or physiological time. By this method, one can determine the conditions under which changes in the parameters of the development rate curve will be most significant to the ecology and evolution of insect life histories. In the examples considered, the most important parameters of the development rate curve were its height, Rm, and its position, Tm. Its spread, Tσ, played a lesser role. The response of development accumulation to changes in these parameters was monotonic, except in the case of variation in position during midsummer for high values of mean annual temperature, in which case increasing Tmmay either increase or decrease development accumulation.