Work

Emergence- and DNA-based detection methods show inconsistent effects of planting date on parasitism of red sunflower seed weevil, Smicronyx fulvus LeConte, by Triaspis aequoris Martin

Year: 2026

Type: article

Abstract: The red sunflower seed weevil, Smicronyx fulvus LeConte, is a univoltine pest of sunflower whose larvae feed inside developing achenes. Feeding by a single larva can reduce seed oil by approximately 30%. Several factors (including pyrethroid resistance) have produced extremely high S. fulvus populations in South Dakota. Though early planting is an effective cultural practice to reduce S. fulvus damage, changes to planting dates may impact natural enemies, including the parasitoid, Triaspis aequoris Martin. To assess effects of early planting on parasitism by T. aequoris, weevil larvae (Smicronyx spp.) were collected from sunflowers planted over the range of crop insurance dates prescribed by the USDA’s Risk Management Agency. Additional larvae were collected from wild sunflower Helianthus annuus L. in several locations. Parasitism was assessed using both emergence- and DNA-based methods. Parasitism ranged from 0.0 - 23.2% in the cultivated samples and 0.0 - 25.0% in the wild, and significant (but inconsistent) effects of planting date were apparent. Smicronyx spp. larvae from wild H. annuus tended to have a lower mass than those from cultivated sunflowers. Key findings were: (1) Triaspis aequoris was the only parasitoid reared from Smicronyx spp. collected in cultivated sunflowers, (2) planting date has an inconsistent effect on parasitism, and (3) wild H. annuus may serve as an insecticide-free refuge of T. aequoris while producing a limited number of less fecund S. fulvus adults, and (4) the DNA-based method is more reliable for assessing parasitism by T. aequoris than the traditional emergence-based method.

Source: Biological Control

DOI: 10.1016/j.biocontrol.2026.106056

Authors: Jeffrey Cluever, Phillip Shults, Angelia Hogness, Caitlin Taylor, Robert R. Kula, Jarrad Prasifka