Smicronyx fulvus

The red sunflower seed weevil can be distinguished from the similar gray sunflower seed weevil (Smicronyx sordidus) by its smaller size (2.5–3 mm vs. ~6 mm), reddish-brown coloration (vs. gray), and more numerous eggs laid per female. S. fulvus is also smaller than the sunflower head-clipping weevil (Haplorhynchites aeneus, ~8 mm) and lacks the metallic black coloration of that species. Within sunflower heads, S. fulvus eggs are laid internally in developing seeds, whereas S. sordidus deposits eggs externally on seeds.

Adult beetles are 2.5–3 mm in length with an elongated body form. The body is covered in reddish-brown scales that rub off as the insect ages, giving older specimens a paler appearance. The overall coloration is uniformly reddish-brown. The species possesses the characteristic rostrum (snout) typical of weevils.

Agricultural fields cultivated with sunflower (Helianthus annuus), including both oilseed and confectionery varieties. Also found on wild sunflower (Helianthus annuus) in non-cultivated areas. Adults occur on sunflower plants from bud stage through maturity.

United States and Canada. Specific records include Alberta, Ontario, and Saskatchewan in Canada, and Vermont in the United States. The species occurs throughout the sunflower-growing regions of North America.

Adults are present during the entire growing season. In Texas and similar regions, adults emerge in late June and early July. Larvae pupate in soil during June or July of the following year. One generation per year.

Adults feed on sunflower buds and pollen. Larvae feed internally on developing sunflower seeds (achenes), consuming approximately one-third of the seed contents before exiting.

• Helianthus annuus - host plantCultivated and wild sunflower; primary host
• Helianthus - host plantGenus-level host association
• Triaspis aequoris - parasitoidParasitoid wasp that attacks larvae
• Nealiolus curculionis - parasitoidBraconid wasp that parasitizes larvae

Univoltine (one generation per year). Adults emerge from soil in late spring to early summer. Females deposit eggs individually into developing sunflower seeds from the edge of the flower disc inward. Each larva consumes approximately one-third of a seed before chewing an exit hole and dropping to the ground. Larvae burrow into soil to overwinter, pupating the following June or July. Adults emerge from pupae to begin the cycle again.

Adults feed between bracts of sunflower buds before flowers open, then shift to feeding on pollen once flowers mature. Females oviposit into developing seeds throughout the blooming period. Mature larvae exit seeds through chewed holes and drop to the ground to burrow into soil for overwintering.

Primary seed-feeding pest of cultivated sunflower in North America. Larval feeding reduces seed oil content by approximately 30% per individual. Serves as host for parasitoid wasps including Triaspis aequoris and Nealiolus curculionis. Wild sunflower populations may act as insecticide-free refugia for natural enemies.

Major economic pest of sunflower production. Action thresholds for insecticide application are 14 adults per head for oilseed sunflowers and 1 per head for confectionery sunflowers. Host plant resistance has been developed, with line HA 488 showing significantly reduced damage (5% vs. 20–38% in susceptible lines). Early planting is an effective cultural practice to reduce damage.

• Smicronyx sordidusGray sunflower seed weevil; larger (~6 mm), gray coloration, lays fewer eggs, deposits eggs externally on seeds rather than internally
• Haplorhynchites aeneusSunflower head-clipping weevil; larger (~8 mm), metallic black, girdles stems below flower heads rather than feeding on seeds

• pest
• agriculture
• sunflower
• seed-feeder
• parasitoid host

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Managing Insect Pests of Texas Sunflowers - AgriLife Extension Entomology
• Meloidae Holdings | Entomology Research Museum
• Bug Eric: More Insects From Sunflowers
• Bug Eric: Wasp Wednesday: Pachysomoides fulvus
• Bug Eric: September 2011
• reintroduction | Blog
• Susceptibility of sunflower inbred lines and putative resistance sources to Smicronyx fulvus LeConte (Coleoptera: Curculionidae)
• 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