Sweet potato weevil (other)

Cylas formicarius ssp. elegantulus

1. Identification

• Common name: Sweet potato weevil (another)
• Scientific name: Cylas formicarius ssp. elegantulus Summers
• Order: Coleoptera
• Family: Brentidae

2. Pest description

• Adults: Weevils 5–7 mm long, with a narrow, elongated body, metallic blue to black colouring, ant-like in appearance; very active at dusk and during the night.
• Larvae: Apodous, whitish, with a curved body and a brown head; they develop inside the roots and underground stems.
• Pupae: Formed inside the roots or in the nearby soil.
• Eggs: Laid in stem fissures, exposed roots or superficial wounds.

3. Main hosts

• Sweet potato, the main host.
• It may also attack other species of Ipomoea, cultivated or wild.

4. Symptoms and damage

• Borings and thin galleries in the roots, with necrosis, darkening and intense odours.
• Deformation of the roots and total loss of commercial quality.
• Borings in the stem, with wilting and reduced plant vigour.
• In severe attacks, total loss of the crop.

5. Biological cycle

• Several generations per year in warm climates, with a continuous cycle.
• Adults live for several months and move little, favouring localised outbreaks.
• Eggs laid on the stem or roots; larvae develop inside for 3–6 weeks.
• Pupation inside the roots or in the soil; adults emerge and restart the cycle.
• Development favoured by high temperatures, light soils and exposed or damaged roots.

6. Monitoring

• Observation of borings and galleries in the roots during harvests or inspections.
• Assessment of plant vigour, especially in plots with a history of the pest.
• Traps with pheromones or food attractants for the detection of adults.
• Reinforced monitoring in nurseries and vegetative propagation areas.

7. Management measures

• Cultural: Removal and destruction of infested roots; crop rotation with non-host species; use of healthy planting material; timely harvesting to avoid prolonged exposure of the roots.
• Preventive: Avoid injuries to the roots during cultural operations; avoid exposure of roots due to deep tillage; elimination of volunteer plants and wild Ipomoea; improvement of soil drainage and cover to reduce oviposition sites.
• Integrated protection: Regular monitoring; intervention only when necessary; practices that reduce the attractiveness of the plants and the survival of larvae in the soil.

Note:

• Compared with Cylas puncticollis, C. formicarius tends to have narrower, more “ant-like” adults, slightly thinner galleries and greater adaptation to dry soils, although both display very similar biology and damage.

Bibliographic references

• EPPO Global Database – Cylas formicarius.
• CABI Invasive Species Compendium – Cylas formicarius.
• FAO – Sweet potato weevil management guidelines.
• Chalfant, R. B. et al. (1990). Ecology and management of sweet potato weevils.