Rape stem weevil

Ceutorrhynchus napi

1. Identification

• Common name: Rape stem weevil
• Scientific name: Ceutorrhynchus napi Gyllenhal
• Order: Coleoptera
• Family: Curculionidae

2. Pest description

• Adults: Weevils 3–4 mm long, with a greyish-brown body covered with fine scales, a short rostrum and geniculate antennae; activity predominantly in spring.
• Larvae: Apodous, whitish, with a curved body and a brown head; they develop inside the petioles and young stems.
• Pupae: Formed inside the stem or in the nearby soil.
• Eggs: Laid in the petioles or at the base of young leaves.

3. Main hosts

• Rapeseed (main host).
• It may also attack other cultivated or wild crucifers, such as Brassica rapa and Sinapis spp.

4. Symptoms and damage

• Borings in the petioles and young stems, with internal necrosis.
• Galleries inside the stem, causing structural weakening.
• Partial wilting, reduced vigour and delayed development.
• Possible predisposition to secondary fungal infections.
• In severe attacks, a significant reduction in yield and lower silique formation.

5. Biological cycle

• One generation per year, with adults active mainly in early spring.
• Adults emerge from the soil and feed on young leaves before egg-laying.
• Eggs laid in the petioles; larvae develop inside for 3–5 weeks.
• Pupation inside the stem or in the soil; adults overwinter until the following spring.
• Development favoured by mild temperatures and the presence of wild crucifers.

6. Monitoring

• Observation of borings in the petioles and young stems.
• Inspection of plants for the detection of internal galleries.
• Assessment of plant vigour, especially in plots with a history of the pest.
• Yellow chromotropic traps can be used for the detection of adults in spring.

7. Management measures

• Cultural: Removal of wild crucifers; crop rotation with non-host species; proper incorporation of crop residues; sowing on dates that reduce coincidence with the peak flight.
• Preventive: Early monitoring in spring; avoid water and nutritional stress; choice of more tolerant varieties when available; avoid excessive densities that favour humid microclimates.
• Integrated protection: Regular monitoring; intervention only when necessary; practices that reduce the attractiveness of the plants and the survival of larvae in the soil.

Bibliographic references

• EPPO Global Database – Ceutorrhynchus napi.
• CABI Invasive Species Compendium – Ceutorrhynchus napi.
• Alford, D. V. (2003). Insect pests of oilseed rape.
• Williams, I. H. (2010). The major insect pests of oilseed rape in Europe.