INDIANA SOYBEAN SYSTEM MODEL (ISSM) .2. MEXICAN BEAN BEETLE MODEL DEVELOPMENT, INTEGRATION AND EVALUATION

An age-structured, distributed delay model was used to simulate the po pulation dynamics of Mexican bean beetle (MBB), Epilachna varivestis M ulsant, a sporadic insect pest of soybeans. The MBB model was integrat ed with a soybean crop model as part of the Indiana soybean system mod el (ISSM). Results indicated that the model was able to capture the es sential aspects of pest dynamics. Life table statistics based on simul ation results were close to observed values for laboratory conditions (simulated intrinsic rate of increase, r = 0.056 and observed r = 0.05 3) and under field conditions (simulated r = 0.011 and observed r = 0. 015). Simulated MBB population patterns and peak values were in good a greement with observed data. Differences between simulated and observe d population patterns of immature MBB stages were greater than that of adults. Incorporation of mortality due to individual rainstorms and o ther weather events, and effect of alternate hosts and movement (secon dary influx, emigration, etc.) seem to be important for simulating soy bean production in a specific field. The model was used to evaluate th e effects of crop variety, planting dates, weather and insect influx p atterns on soybean yield. Results from simulation experiments showed t hat 'Williams 82' variety was more susceptible to yield loss (up to 45 %) from MBB infestations, than the earlier maturing 'Century 84' (up t o 25% yield loss). This susceptibility is due to the coincidence of th e vulnerable crop stage (pod-setting and seed-filling stages) with the occurrence of the peak populations of MBB stages which cause most of the damage. Late planting tends to mitigate this susceptibility. As th e influx patterns determine the extent of yield loss, the timing and m agnitude of insect influx should be detected and estimated using timel y scouting of fields.