The mealy plum aphid, Hyalopterus pruni (Geoffroy) (Hemiptera: Aphididae) is a pest of prune trees in California. The impact of aphids as pests is well characterized by their population growth rate, a parameter integrating their age-specific development, survivorship, and fecundity. These population parameters were measured at five constants temperatures on potted prune trees. Development rates increased with temperature up to an optimum. The relationship between development rate and temperature was described by linear and nonlinear models. Developmental threshold temperature was greater for the nonlinear model than for the linear model. Thermal requirement for development and maximum lethal temperature determined by these models were similar to those for other aphids. The greatest proportional survivorship of nymphs occurred at 26°C. Mean daily fecundity was lowest at 14°C and highest at 22°C. Adult longevity decreased with temperature. Population growth rates for H. pruni were estimated from measurements of fecundity and development time and were highest at 22°C. This is the first study to document the temperature dependence of the life history parameters for H. pruni and the first to generate a degree-day model for the prediction of phenological events.