Thermal Biology, Overwintering, and a Degree-Day Model for the Adult Emergence of the Red Sunflower Seed Weevil (Coleoptera: Curculionidae)

Abstract

Red sunflower seed weevil, Smicronyx fulvus LeConte, is a univoltine seed-feeding weevil that is a primary pest of cultivated sunflower, Helianthus annuus, in North America, especially within the upper Great Plains region. This pest spends its final larval stage overwintering in the soil before pupating in the summer and emerging as an adult to feed on sunflower pollen and lay eggs in developing achenes. Larval feeding can damage of up to 83% of seeds on a head. Growers typically manage S. fulvus by using insecticides; however, early planting dates have also been demonstrated to reduce weevil damage. It is important to understand how overwintering conditions impact larval development and develop a model to predict adult emergence. Larvae were found to overwinter in the soil at depths that are not subject to temperatures near their freezing point, and a degree-day model was created for emergence.