Smicronyx sordidus

Adults can be distinguished from the related red sunflower seed weevil (Smicronyx fulvus) by coloration: S. sordidus is pale gray, while S. fulvus is reddish-brown. S. sordidus is also larger, approximately 6–8 mm versus about 3 mm for S. fulvus. Adults may be present throughout the growing season, whereas S. fulvus has more defined emergence patterns. The gray sunflower seed weevil lays fewer eggs per seed than S. fulvus, though this is not a field identification character.

Agricultural habitats dominated by sunflower cultivation; also associated with volunteer and wild sunflowers that serve as reservoir hosts. Adults feed on sunflower buds, bracts, and pollen prior to seed infestation.

North America; recorded from the United States and Canada (Manitoba). Distribution corresponds to the range of cultivated sunflower production, particularly in the Great Plains and Texas.

Adults are present throughout the sunflower growing season. Reproductive activity occurs in June. Larvae overwinter in soil after exiting seeds in late summer or fall. A single generation occurs per year.

Adults feed on sunflower buds, bracts, pollen, and occasionally plant tissues. Larvae feed exclusively on developing sunflower seeds, destroying the kernel from within.

• Helianthus annuus - primary hostCultivated sunflower; both oilseed and confectionery varieties. Adults feed on floral structures, larvae develop in seeds.
• Helianthus spp. - hostWild and volunteer sunflowers serve as reservoir hosts.

Univoltine (one generation per year). Adults emerge and feed on sunflower buds and bracts. Females deposit eggs individually into developing seeds at the base of the seed. Larvae hatch and consume the kernel internally. Mature larvae exit seeds, drop to the ground, and burrow into soil to overwinter. Pupation occurs in spring, with adults emerging to coincide with sunflower growth.

Females select sunflower heads with buds nearing anthesis for oviposition, allowing egg placement at the base of developing seeds. Adults may feed between bracts when sunflowers are in bud stage, transitioning to pollen feeding as flowers mature. Larval exit from seeds involves dropping from the head to the soil surface.

Seed predator; reduces seed viability and yield in sunflower crops. Population levels are typically subeconomic but can reach damaging densities under favorable conditions. Not documented as providing significant ecological benefits.

Agricultural pest of sunflower, particularly damaging to confectionery and hybrid seed sunflowers where individual seed quality is economically important. The action threshold is higher than for the red sunflower seed weevil due to lower fecundity, though precise economic thresholds remain unestablished. Management relies on monitoring, cultural practices (volunteer sunflower control, crop rotation), and insecticide application when warranted.

• Smicronyx fulvusRed sunflower seed weevil; distinguished by reddish-brown coloration, smaller size (~3 mm), and higher fecundity. S. fulvus has established economic thresholds (1 per head for confectionery sunflowers), while S. sordidus thresholds remain undefined.

• agricultural pest
• sunflower
• Curculionidae
• seed feeder
• North America
• univoltine

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Managing Insect Pests of Texas Sunflowers - AgriLife Extension Entomology
• Grasshoppers of Colorado
• Grasshoppers of Colorado
• Grasshoppers of Colorado
• Grasshoppers of Colorado
• Dusky Grasshopper