Spatial prediction of corn rootworm (Coleoptera: Chrysomelidae) adult emergence in Iowa cornfields.

The most common management options for corn rootworms are rotating corn with nonhost crops, planting genetically engineered corn resistant to corn rootworms (e.g., Bacillus thuringiensis [Bt] corn), and treating with a soil insecticide at planting time. Because these control tactics are preventive, the decision to apply controls has been made without any knowledge of rootworm density and spatial distribution. This study was conducted to predict the spatial distribution of adult emergence and to generate and test management zones for insecticides and Bt corn. To identify variables that correlated best with adult emergence the following year, plant height, plant stage, soil moisture, altitude, and corn rootworm adults were sampled spatially and temporally. Correlation and regression analyses showed that the best prediction for the adult emergence the following year was adult counts in the ear zone at peak population densities during the present year. Based on the prediction, geostatistics and the geographic information system were used to generate and test prescription maps with management zones for insecticides and Bt corn. Map-overlaying analysis showed that management zones for insecticides based on the economic injury level and Bt corn with 20% refuge had potential failure of 3-15% and 0-12% of field areas, respectively. This study demonstrated the spatial prediction of adult emergence the following year and generation of management zones, which has the potential of preventative, site-specific management of corn rootworms.