The alfalfa root weevil, Sitona discoideus (Coleoptera: Curculionidae), is an important pest of alfalfa. The developmental rates of the embryo development were recorded at eight constant temperatures ranging from 8.5 to 30°C. Using 10 models (1 linear and 9 nonlinear), we evaluated the relationship between constant temperature and developmental rate. Embryo development was shortest (8.5 d) and longest (69 d), at 28 and 8.5°C, respectively. The threshold temperature (T₀) and the thermal constant (K) were estimated using linear regression to be 4.7°C and 207.7 DD, respectively. The two most efficient nonlinear models, the Lactin and the Sharp and DeMichele, gave estimates of T_min and T_max of 4.4 and 3.9 and 30.0 and 30.9°C, respectively. This information has potential application in predicting the suitability and optimal time of release of an egg parasitoid of S. discoideus.