SPATIAL MODEL FOR SIMULATING CHANGES IN TEMPERATURE AND INSECT POPULATION-DYNAMICS IN STORED GRAIN

A spatial model describing insect population dynamics in a grain bin was developed by coupling a model of Cryptolestes ferrugineus (Stephens) with a two-dimensional bin temperature model. In the model, the bin is divided into 16 compartments. The insect model is run separately for each compartment. This allows the insect model to simulate different population growth rates based on each compartment's average daily temperature. Field data for a 351-m3 (10,000 bu) bin located in Cloud County, KS, was used to validate the model. The model predicted grain temperatures accurately for each of the nine compartments, except the center top portion of the grain mass. In this region, observed grain temperatures were 8-degrees-C higher than predicted during December. This may have been caused by convective air movement. In general, the model accurately predicted insect density for most of the bin compartments. However, the model tended to overestimate insect density in the center of the grain mass during the end of the storage period in December. During this period, actual grain temperatures were still optimal for C. ferrugineus growth. Cephalonomia waterstoni (Gahan), a common host-specific parasitoid of C. ferrugineus, may have been responsible for the pest population decrease.