Development and validation of a model for predicting survival of young larvae of Tribolium castaneum exposed to elevated temperatures during heat treatment of grain-processing facilities

Heat treatment involves raising the ambient temperature of grain-processing facilities to 50–60 °C for at least 24 h to manage stored-product insects. The young larvae (first instars) of the red flour beetle, Tribolium castaneum (Herbst), are the most heat tolerant stage at temperatures of 50–60 °C when compared to eggs, old larvae, pupae, and adults. A thermal death kinetic model was developed to predict survival of T. castaneum young larvae exposed to six constant elevated temperatures between 42 and 60 °C. The model was based on two non-linear relationships: 1) logarithmic decrease in survival of larvae as a function of time, and 2) logarithmic decrease in larval survival as a function of temperature. The model was validated with 12 time-dependent temperature datasets collected during actual heat treatments of pilot-scale flour and feed mills and a commercial grain-processing facility. The observed survival of larvae in plastic boxes/vials with flour was used to validate model predictions. The heating rate to reach 50 °C from the ambient temperature, among the 12 datasets ranged from 0.9 to 7.8 °C/h. The mean absolute deviation between observed and predicted larval survival for 10 of the 12 datasets ranged from 2.1 to 11.4%; for the other two datasets it was 16.2 and 18.3%. These results show that the thermal death kinetic model can be used to predict survival of young larvae of T. castaneum based on time-dependent temperature profile obtained at any given location during heat treatment of grain-processing facilities.