Sitonini

Sitonini weevils can be distinguished from other Entiminae tribes by their association with Fabaceae hosts and their characteristic feeding damage: adults produce U-shaped notches on leaf margins, while larvae are subterranean root-nodule feeders. The tribe comprises seven extant genera: Andrion, Charagmus, Coelositona, Eugnathus, Schelopius, Sitona, and Velazquezia, plus the fossil genus †Sitonitellus. Species-level identification requires examination of genitalia and other morphological details.

Associated with Fabaceae host plants across diverse environments from lowlands to altitudes exceeding 1000 m. Agricultural populations thrive on light sandy soils and sandy loams. Overwintering adults shelter in perennial host plants such as Lupinus polyphyllus and Cytisus scoparius.

Holarctic native distribution. Charagmus griseus historically widespread across the West Palaearctic including Europe and North Africa. Charagmus gressorius distributed across the Central-Asiatic–European–Mediterranean region including Turkey, Macaronesia, the Caucasus, and Central Asia to Kazakhstan. Both species have expanded throughout Europe, reaching Scandinavia and Baltic countries by the early 2010s.

Adults emerge from overwintering sites when lupin seedlings emerge in spring. Activity continues through the growing season until adults return to overwintering sites in perennial hosts.

Adults feed on leaves of leguminous plants, particularly lupins (Lupinus spp.), producing characteristic U-shaped notches. Larvae feed exclusively on root nodules of Fabaceae, including Lupinus angustifolius, L. albus, L. luteus, L. polyphyllus, Cytisus scoparius, Genista, and Ornithopus. Members are adapted to quinolizidine alkaloids present in host plants.

• Lupinus angustifolius - larval host (root nodules), adult host (leaves)narrow-leaved lupin; major crop host in Europe
• Lupinus albus - larval host (root nodules), adult host (leaves)white lupin; major crop host
• Lupinus luteus - larval host (root nodules), adult host (leaves)yellow lupin
• Lupinus polyphyllus - overwintering shelter, larval host (root nodules), adult host (leaves)perennial host for overwintering adults
• Cytisus scoparius - overwintering shelter, larval host (root nodules), adult host (leaves)perennial host for overwintering adults
• Genista - larval host (root nodules), adult host (leaves)
• Ornithopus - larval host (root nodules), adult host (leaves)
• Bradyrhizobium - indirect interactionsymbiotic nitrogen-fixing bacteria in root nodules consumed by larvae

Adults overwinter in perennial host plants and emerge when spring seedlings appear. After feeding and mating, females deposit yellowish-white ellipsoid eggs on plants and soil surface; eggs darken after 2–3 days and are washed into soil by rain. Larvae develop underground, feeding on root nodules through multiple instars (4–5 instars inferred from related Sitona species). Pupation occurs in soil. New adults emerge and seek overwintering sites in perennial hosts.

Adults exhibit cryptic behavior that complicates detection and control. Feeding produces distinctive U-shaped notches on leaf margins with negligible economic impact compared to larval damage. Larval feeding on root nodules causes major economic damage by reducing nitrogen fixation and creating lacerations that admit soil-borne pathogens. A potential mutualistic interaction with Fusarium fungi has been observed, where higher larval survival occurs on infected plants.

Significant agricultural pests of legume crops, particularly lupins, causing up to 40% grain yield reduction in L. angustifolius. Larval feeding severely impairs nitrogen fixation in root nodules. Root damage facilitates entry of soil-borne plant pathogens including Fusarium spp., Phoma spp., Pythium spp., Rhizoctonia spp., Sclerotinia spp., and Thielaviopsis basicola. A pathogen vector role has been hypothesized but not confirmed.

Major pests of lupin cultivation in Europe, especially in north-eastern Germany and Poland. Infestations necessitate integrated pest management combining insecticide applications with ecological methods. Economic impact stems primarily from larval root-nodule feeding rather than adult leaf damage.

• Other Entiminae tribesDistinguished by Fabaceae host specificity and root-nodule feeding habit of larvae; most other broad-nosed weevils have broader host ranges or different larval feeding strategies

• pest
• agriculture
• Fabaceae
• root nodule feeder
• Holarctic
• lupin pest
• nitrogen fixation impact

• BugGuide
• Wikipedia
• iNaturalist taxon
• NCBI Taxonomy
• Lupin Root Weevils (Charagmus spp., Curculionidae: Sitonini), a Lupin Pest: A Review of Their Distribution, Biology, and Challenges in Integrated Pest Management