Degree-day and precipitation provides insights in wheat stem sawfly population dynamics in Colorado

Wheat stem sawfly (WSS), Cephus cinctus (Hymenoptera: Cephidae), is a native grass-feeding insect and one of the most important pests of wheat in North America. Yield losses from WSS can be due to stem boring and/or stem cutting which causes plants to lodge. In 2022, WSS have caused an estimated $40 million loss in Colorado winter wheat production. Estimation of WSS emergence and population density can help wheat growers implement strategies to suppress this insect pest population. For this study, wheat fields were sampled between 2016 and 2022 using a sweep net, starting in the end of April every year. Between six and nine fields were sampled in New Raymer/Orchard (Colorado) each year. Data on temperature, rain, and snowfall were collected from two meteorological stations in northwestern Colorado, close to the wheat fields. This seven-year data was used to analyze correlation between weather variables and WSS adult emergence, adult flight peak, and population density. We observed significant correlation between WSS emergence and precipitation. Further, this data will be used to provide estimates on degree-day accumulation (heat units) and precipitation (mm) necessary to trigger WSS important biological events to be incorporated in this insect pest management. This study aims to provide information that can potentially help reduce the damage caused by WSS in wheat.