Development and validation of models for predicting the seasonal emergence of corn rootworm (Coleoptera: Chrysomelidae) beetles in Iowa

Effective management of adult northern and western corn rootworms, Diabrotica barberi Smith & Lawrence and D. virgifera virgifera LeConte, respectively, requires knowledge of their emergence pattern so that scouting and adult insecticide applications can be accurately timed. The objective of this study was to develop and validate species- and sex-specific models that reliably predicted adult corn rootworm emergence in Iowa. Prediction began from a biofix defined as the date of first beetle emergence in a field. The models were fit with a 3-parameter Weibull function using emergence data collected in 57 Iowa cornfields over 5 yr. Models were validated with emergence data collected in 21 additional fields from a separate year. A single Pherocon CRW Trap per field was as effective as 13 emergence cages per field at detecting the biofix. Air temperature degree-days accumulated from the emergence cage biofix explained 85% of the variability in total corn rootworm emergence over 5 yr. This model explained 89% and 83% of the variability in total beetle emergence observed in the validation year from the emergence cage and Pherocon CRW Trap biofixes, respectively. These models do not eliminate scouting for adult corn rootworms but should improve the scouting efficiency by allowing growers to focus scouting to key periods, such as peak beetle emergence, when populations should be at their maximum abundance in the field.