The present study is the first attempt in Egypt which focused on determining the development rate of Spodoptera frugiperda at different constant temperatures, the number of degree-days (DD's) required for each stage to complete development, as well as the degree-days required for overall egg-to-adult development. The study was conducted under three constant temperatures (20, 25, and 30 °C at the Department of Zoology, Faculty of Science, South Vally University, Qena Governorate, Egypt.
           The aim of this study was to determine the development rate of S. frugiperda at different temperatures and to calculate the number of degree-days (DD's) required for each stage to complete its development. The study showed that the mean incubation period was6.9, 3.4, and 2.1 days at 20, 25, and 30 °C, respectively, and the larval duration were 38.5, 23.7, and 18.6 days at the same temperatures, respectively. On the other hand, The average pupal durations were 22.5  at 20,  9.4  at 25, and 7.7days at 30°C. For the adult stage the mean time required for maturation of the ovaries and starting to egg-laying, decreased as the temperature increased, from 4.8 days at 20°C to 2.1 days at 30°C. Meanwhile, the mean duration of generation for S. frugiperda was 72.7, 40.1, and 30.5 days at 20, 25, and 30°C, respectively. The lower threshold of development (t₀) and average thermal units in degree-d (dd's) were 15.79 °C and 30.0 dd's for egg stage; 10.39 °C and 360.2 dd's for the larval stage;  14.05 °C and 129.8 dd's for the pupal stage; 12.95 °C and 37.73 dd's for pre- oviposition period and 12.49°C and 527.3 dd's for a complete generation. The study of heat requirementsof the fall armyworm as a new invasive pest came to Egypt from the South Africa countries is very important to determine the thermal heat units for the development and growth of this pest in order to predict the annual field generations in other supplementary studies and draw up a planning IPM strategy for this dangerous pest during the absence of any local information about it.