Predicting corn rootworm egg density: analyzing soil characteristics and cropping intensity across the Midwest

Diabrotica virgifera virgifera and Diabrotica barberi represent two important insect pests affecting maize production across the United States.  Where and when Diabrotica will become a problem continues to be a challenging aspect of minimizing the impact of their infestation.  The primary objective of this study was to determine the greatest predictors of Diabrotica egg and associated Diabrotica DNA prevalence in fields across the Midwestern United States.  A secondary objective was to determine the distribution of Diabrotica eggs within fields and learn if aggregations exist.  We evaluated Diabrotica egg count and quantitative PCR estimates of DNA prevalence over eight years and across six states, to determine the most significant factors influencing egg abundance and qPCR Ct scores.  We hypothesized that maize cropping intensity was the primary driver of egg density, with soil factors as secondary drivers.  Landscape-level maize cropping intensity was extracted from the National Agricultural Statistics Service Cropland Data layers and soil data layers were obtained from the Soil Survey Geographic Database and these data were utilized as predictor variables at each field.  Principal component analysis indicated that aspect (slope orientation) (0.47) and soil k factor (0.39) explained the most variation across all fields.  Spatial analysis by indices (SADIE) was performed to determine egg distributions within fields and initial results indicate varying levels of aggregation.  Results from this study will provide insights into the relationships between soil characteristics and Diabrotica egg abundance across a wide geographical scale, as well as provide a foundation for further risk assessment mapping of Diabrotica.