An insect mortality model is discussed which was developed to cater for a range of grain temperatures and moisture contents, and also account for Wadley°¦s problem where control mortality is unknown. This occurs, for example, when treated immature stages are hidden within grain kernels or eggs are buried in substrate. In the model the expected survival from a given treatment is multiplied by the probability P, which is obtained by a linear predictor ƒØ on the scale of a given transformation (probit, logit, complementary log-log). The fiducial limits for the lethal time estimates (LTs) at a given percentage mortality are obtained by a linear Taylor expansion of ln(LT). The model has been used to estimate variation in mortality response of development stages of Rhyzopertha dominica and Sitophilus oryzae, and to estimate the added impact of grain moisture content in the case of R. dominica. It has also been useful for estimating the impact of the initial rate of heating on the rate of mortality of R. dominica and for comparing the heat tolerance of eggs from three species of psocids.