Technical Abstract: The tropical sod webworm, Herpetogramma phaeopteralis Guenée is a major turfgrass pest in the southeastern United States. We evaluated larval development on five artificial diets and at six temperatures (15, 20, 25, 30, 32.5, 35 ±1 °C) on St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze]. Only individuals fed on St. Augustinegrass and soy-wheat germ diets were able to complete their lifecycles. None of artificial diets tested (corn-based, soy-wheat germ, corn cob-wheat germ, corn cob-soy flour, or Pinto bean) were suitable for rearing this species, due to high mortality and slower developmental time. The total developmental time (from oviposition to adult) on S. secundatum significantly decreased from 47.8 d at 20°C to 21.1 d at 30°C, and then increased to 32.6 d at 32.5°C. Tropical sod webworm failed to complete larval development at 15 and 35°C. The relationship between temperature and developmental rate was described using two linear (common and polynomial) and two nonlinear models (Briere-1 and Briere-2). The estimated lower temperature thresholds using a linear model for eggs, first, second, third, fourth, fifth, and sixth instars, prepupa, pupa and the total development were 10.1, 6.9, 12.3, 10.5, 15.3, 13.9, 9.1, 13.1, 12.0 and 13.1°C, and the thermal constant of these stages were 62.9, 66.2, 38.2, 40.3, 24.9, 32.3, 51.9, 106.4, 109.9 and 370.4 degree-days (DD), respectively. The Briere-1 model provided the best fit with estimated lower, upper and optimum thresholds for total development of 14.9, 34.3 and 29.4°C, respectively. The developmental requirements of H. phaeopteralis can be used to help predict the distribution and seasonal phenology of this pest.