Abstract

An age-structured, distributed delay model was used to simulate the population dynamics of Mexican bean beetle (MBB), Epilachna varivestis Mulsant, a sporadic insect pest of soybeans. The MBB model was integrated with a soybean crop model as part of the Indiana soybean system model (ISSM). Results indicated that the model was able to capture the essential aspects of pest dynamics. Life table statistics based on simulation results were close to observed values for laboratory conditions (simulated intrinsic rate of increase, r = 0.056 and observed r = 0.053) and under field conditions (simulated r = 0.011 and observed r = 0.015). Simulated MBB population patterns and peak values were in good agreement with observed data. Differences between simulated and observed population patterns of immature MBB stages were greater than that of adults. Incorporation of mortality due to individual rainstorms and other weather events, and effect of alternate hosts and movement (secondary influx, emigration, etc.) seem to be important for simulating soybean production in a specific field.

The model was used to evaluate the effects of crop variety, planting dates, weather and insect influx patterns on soybean yield. Results from simulation experiments showed that ‘Williams 82’ variety was more susceptible to yield loss (up to 45%) from MBB infestations, than the earlier maturing ‘Century 84’ (up to 25% yield loss). This susceptibility is due to the coincidence of the 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 the influx patterns determine the extent of yield loss, the timing and magnitude of insect influx should be detected and estimated using timely scouting of fields.