The developmental periods and mortality of the immature stages of field boll weevils at 18, 22, 26, 30, and 34°C were determined. Cotton branches containing squares into which a boll weevil egg had recently been deposited were placed into plastic Aquapics® in temperature controlled cabinets in which direct sunlight was simulated. Abscissed squares were transferred to chambers in which sub-canopy lighting was simulated. Subsamples of squares were dissected and the stage of development and mortality recorded. The optimum developmental temperature for the North Carolina boll weevil strain was ca. 30°C, since mortality was at a minimum at that temperature and developmental times at 30° and 34°C were very nearly the same.