Dynamic model for predicting survival of mature larvae of Tribolium confusum during facility heat treatments

Structural heat treatment, a viable alternative to methyl bromide fumigation, involves raising the ambient temperature of food-processing facilities between 50 and 60 degrees C by using gas, electric, or steam heaters, and holding these elevated temperatures for 24 h or longer to kill stored-product insects. A dynamic model was developed to predict survival of mature larvae, which is the most heat-tolerant stage of the confused flour beetle, Tribolium confusum (Jacquelin du Val), at elevated temperatures between 46 and 60 degrees C. The model is based on two nonlinear relationships: 1) logarithmic survival of T. confusum mature larvae as a function of time, and 2) logarithmic reduction in larval survival as a function of temperature. The dynamic model was validated with nine independent data sets collected during actual facility heat treatments conducted on two separate occasions at the Kansas State University pilot flour and feed mills. The rate of increase of temperature over time varied among the nine locations where mature larvae of T. confusum were exposed, and the approximate heating rates during the entire heat treatment ranged from 1.1 to 13.2 degrees C/h. The absolute deviation in the predicted number of larvae surviving the heat treatment was within 3-7% of the actual observed data. Comparison of the absolute deviation in the time taken for equivalent larval survival showed that the model predictions were within 2-6% of the observed data. The dynamic model can be used to predict survival of mature larvae of T. confusum during heat treatments of food-processing facilities based on time-dependent temperature profiles obtained at any given location.