Red Sunflower Weevil: Appearance, Territory, Damage and Life Cycle

Latin Name: Smicronyx Fulvus

Appearance: The most frequent of the two species that may be found in the Prairies is the red sunflower seed weevil (Smicronyx fulvus). Adults are 2.5 to 3 mm (1/10 to 1/8 in.) long and have reddish-orange, oval scales. The larvae are found in the upper third of growing sunflower seeds. This is a little, reddish-brown weevil that is 3.0 – 4.0 mm (1/8 inch) in length. Adults can be found eating on pollen on the faces of flowering sunflowers or hidden beneath the flower bracts. Infested seeds are not distinguishable from healthy seeds; however, they will have an exit hole towards the top once the larva has developed and fled.

Hosts Plants: Sunflower

Territory: North and South Dakota and Minnesota

Damage Insect Cause: Larvae feed on the seed’s inner flesh. Some seeds are completely swallowed, while the majority are just half digested. Larvae that emerge from storage will die without harming the seeds, but their carcasses will stay in the container. Early planting dates likely to decrease damage since the red seed weevil is a late-emerging pest, but planting date manipulation alone cannot be relied on to offer control. Tillage has been shown to reduce overwintering weevil survival, although it is not suggested in locations where soil moisture conservation is critical. While sunflower moth treatments generally coincide with periods of weevil activity, allowing for simultaneous control of both pests, fields should be inspected for red seed weevil before applying any treatments.

Life History and Habits: The adults arrive on volunteer sunflowers in late June and feed on the bracts, where they leave tiny holes. Adults travel to the inflorescence and feed on pollen generated by the disk flowers as the bud grows and opens. Females place their eggs inside the growing seed coat. Plant populations are at their peak during 50% anthesis. The egg laying pattern follows the seed filling pattern, which moves from the outside to the center of the head. A single larva is usually found in an affected seed. The larvae are tiny, cream-colored, legless, and C-shaped. The adult larva chews an exit hole in the seed in late August, slides to the ground just under the sunflower head, and spends the winter in the soil. Pupation takes place in the soil from early June until early July.