Development and Validation of Models for Predicting the Seasonal Emergence of Corn Rootworm (Coleoptera: Chrysomelidae) Beetles in Iowa

Abstract

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-specic models that reliably predicted adult corn rootworm emergence in Iowa. Prediction began from a biox dened as the date of rst beetle emergence in a eld. The models were t with a 3-parameter Weibull function using emergence data collected in 57 Iowa cornelds over 5 yr. Models were validated with emergence data collected in 21 additional elds from a separate year. A single Pherocon CRW Trap per eld was as effective as 13 emergence cages per eld at detecting the biox. Air temperature degree-days accumulated from the emergence cage biox 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 bioxes, respectively. These models do not eliminate scouting for adult corn rootworms but should improve the scouting efciency by allowing growers to focus scouting to key periods, such as peak beetle emergence, when populations should be at their maximum abundance in the eld.