Validation of a nested error component model to estimate damage caused by corn rootworm larvae

The corn rootworm complex (Coleoptera: Chrysomelidae) constitutes a significant threat to maize production in the United States. We conducted an analysis of readily available field trial data to validate an existing damage function for corn rootworm larvae. We used a nested error component model with unbalanced panel data to describe the relationship between yield loss and root injury caused by these insects. These data were collected by personnel with the Insect Management and Insecticide Evaluation Program (Department of Crop Sciences, University of Illinois) and represent 19 location-years. To our knowledge, this is the largest dataset used to estimate a damage function for corn rootworm larvae. Unlike many experiments examining the relationship between root injury and yield loss caused by corn rootworm larvae, the dataset used for our analysis includes many Bt maize hybrids. Our model suggests that for each node of roots injured by corn rootworm larvae, a yield loss of approximately 15% can be expected. Statistically significant variance components included an effect of location and experimental error. We speculate that variation in weather across experimental sites was the principal factor contributing to the significant effect of location. The substantial experimental error observed for our model highlights the limitations of utilizing a multi-year, geographically diverse damage function for predicting yield loss due to root injury on a small scale. We discuss major factors contributing to the variance components estimated by our model and suggest techniques for improving future analyses of the damage function for corn rootworm larvae.