Developmental times and survival rates of the immature stages of Diorhabda elongata Brullé (Coleoptera: Chrysomelidae), a biological control agent of saltcedar (Tamarix spp.), were studied in the laboratory at six constant temperatures (15–40°C). At 15 and 40°C, eggs did not develop and sustained 100% mortality. Similarly, larvae at 15°C and pupae at 40°C did not develop and sustained 100% mortality. For all three larval stages, the developmental time decreased with increasing temperature between 20 and 35°C and increased at 40°C. Developmental times also decreased with increasing temperature between 20 and 35°C for the pupal stage as did total developmental time from egg to adult. Both linear and nonlinear models were used to describe the relationship between developmental rates (1/d) and temperature (°C) and to determine stage-specific lower and upper developmental thresholds, respectively. The lower developmental thresholds, calculated using the linear model, ranged from 6 to 15°C for all life stages. Using the nonlinear model, the lower developmental thresholds ranged from 15 to 18°C for all life stages. Likewise, the high temperature thresholds for the first-, second-, and third-instar larvae, pupae, and total development ranged between 40 and 42°C. Results from this study were used to enhance the efficiency of mass-rearing methods for open field releases of D. elongata in California. More importantly, this study is the first step in the construction of a detailed population simulation model to predict field phenology and density of D. elongata to further optimize the use of this biological control agent in managing saltcedar in the western United States.