Development of a degree-day model for adult emergence of the red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae)

Authors: PANTZKE, SHAWNA - North Dakota State University; Rajamohan, Arun; FERGUSON, BETH - Former ARS Employee; Rinehart, Joe; PRISCHMANN-VOLDSETH, DEIRDRE - North Dakota State University; Prasifka, Jarrad

Submitted to: Journal of Kansas Entomological Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2024
Publication Date: 6/24/2024
Citation: Pantzke, S., Rajamohan, A., Ferguson, B., Rinehart, J.P., Prischmann-Voldseth, D.A., Prasifka, J.R. 2024. Development of a degree-day model for adult emergence of the red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae). Journal of Kansas Entomological Society. 97(1):26-38.
DOI: https://doi.org/10.2317/0022-8567-97.1.26

Interpretive Summary: The red sunflower seed weevil is a serious seed-feeding pest of sunflower in North America. Sunflower growers usually apply insecticides to limit weevil damage, but there are other strategies like early planting that could also help. To make alternative strategies easier to use, a simple model was created for the amount of heat and time (degree-days) needed for adult weevils to emerge from the soil. Weevil larvae brought into the lab needed soil temperatures of at least 5°C to continue developing. The first adult weevils emerged at about 970 degree-days and half of all adults emerged after about 1160 degree-days. Weather station data from probes 5 cm under grass or 10 cm under bare soil were both useful for predicting weevil emergence. The degree day model prediction was good when the soil was partially shaded by a spring crop (wheat), but the model prediction was late when soil was kept bare (and heated up faster). Because the degree-day model is similar to models used for crop development, sunflower growers can use this model to predict planting times that will avoid much of the damage caused by the red sunflower seed weevil.

Technical Abstract: The red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae), is the most destructive seed-feeding pest of sunflower in North America. The life history of S. fulvus (e.g., univoltine, overwintering within ˜ 5 cm of soil surface) suggests several strategies to limit crop damage, but insecticides remain the primary management tool. To facilitate broader management of S. fulvus, a degree-day model for adult emergence was developed and tested. Emergence of adults under controlled conditions produced a lower developmental threshold of 5°C, ˜ 970 degree-days to first emergence, and ˜ 1160 degree-days to 50% emergence. Soil temperature data showed accumulated degree-days were similar 5 cm below turf and 10 cm beneath bare soil. Observed emergence of weevils in field plots occurred several days earlier than predicted (using 5 cm turf or 10 cm bare soil temperatures) when soil was kept free of vegetation, but was similar to predicted emergence when plots were shaded by spring wheat, which is representative of crops planted after sunflower for much of North America. Though access to soil (rather than ambient)temperature data are needed, this first degree-day model provides a tool to help growers avoid S. fulvus damage using early planting or early-maturing hybrids.