Mortality of boll weevil,Anthonomus grandisBoheman, larvae and pupae resulting from exposure to high temperatures can be partitioned into two categories, “desiccation” and thermal death. Larvae and pupae that die from thermal death turn a greybrown color after death, do not move when probed or squeezed, and lose the resiliency of their integument. Those dying from “desiccation” will show the same characteristics but do not turn the grey-brown color; they generally retain the same color as live insects but have a very dried-out appearance. Thermal death is a function of exposure time and high temperatures. Low levels of thermal mortality appear in ≤3 h at 54.4°C. An estimated 99% mortality should result from a 2-h 18-min exposure at 60°C. Because soil surface temperatures sometimes reach 60°C, high temperatures may be an important cause of mortality in some locations. A model for forecasting time and temperature thresholds for thermal mortality is presented.