Modeling the spread of western corn rootworm (Coleoptera: Chrysomelidae) populations adapting to soybean-corn rotation

A behavioral change in some western corn rootworm, Diabrotica virgifera virgifera LeConte, populations is threatening the effectiveness of crop rotation, a successful management strategy for controlling this pest. We created a simple meteorological and behavioral model that can be used to predict the spread of the beetle infesting soybean, Glycine max (L.), throughout the Midwest. We used data collected in Illinois, Indiana, Michigan, and Ohio to create maps of observations to evaluate the model. We displayed data on the maps using thresholds of 10, 20, and 40 western corn rootworm beetles per 100 sweeps. Counts above a threshold represent populations searching for plants other than corn, Zea mays L., and adapted to the soybean-corn rotation. According to our model, the population adapted to soybean spreads 10-30 km per year depending on the directions of the prevailing storms and winds. The model underestimates the observed spread to the south. The model fits the Illinois data best when a threshold of 10 adults per 100 sweeps is used to visualize data and test the model. The model fits the Michigan data better with a threshold of 20 beetles, but is insensitive to the visualization and evaluation threshold for other areas. Model results support the hypothesis that the origin of the population of western corn rootworm infesting soybean is Ford County, IL. We predict that populations of western corn rootworm will be infesting soybean in much of Ohio, lower Michigan, and southern Wisconsin during the next 5 yr and eastern Iowa within the next 10 yr.