Cabbage webworm

Hellula undalis

1. Identification

• Common name: Cabbage webworm
• Scientific name: Hellula undalis Fabricius
• Order: Lepidoptera
• Family: Crambidae

2. Pest description

• Caterpillars cream to brownish in colour, with well-defined longitudinal brown lines.
• Narrow, very mobile body, curling up when disturbed.
• Small adults, with brownish forewings showing wavy patterns and pale hindwings.
• Polyphagous species, with a strong preference for Brassicaceae.
• It attacks young leaves, veins, shoots and growing points.

3. Main hosts

• Head cabbage.
• Cauliflower.
• Broccoli.
• Kale.
• Radish.
• Turnip greens.
• Other cultivated and wild Brassicaceae.

4. Symptoms and damage

• Mines and galleries in young leaves, especially near the veins.
• Irregular perforations and extensive scraping.
• Damage to the apical meristem, potentially destroying the growing point.
• Curling of the leaves due to the presence of webs.
• Reduced development and yield losses.
• In seedlings, it can cause plant death.

5. Biological cycle

• Several generations per year, accelerated in hot, dry climates.
• Eggs laid singly or in small groups on the underside of the leaves.
• Caterpillars initially leaf-mining and then feeding externally.
• Pupation in the soil or among plant debris.
• Adults active over long periods in tropical and subtropical regions.

6. Monitoring

• Observation of mines, scraping and perforations on young leaves.
• Inspection of the growing point and of leaves curled with webs.
• Pheromone traps for detection and monitoring of flights.
• Assessment of the percentage of plants with symptoms, especially in seedlings and transplants.

7. Management measures

• Cultural: destruction of crop residues, crop rotation and control of wild host plants.
• Preventive: choice of more tolerant varieties, use of insect-proof nets, practices that reduce the attractiveness of young plants and balanced management of nitrogen fertilisation.
• Biological: application of Bacillus thuringiensis on young caterpillars and promotion of natural parasitoids.
• Integrated protection: monitoring with pheromones, definition of intervention thresholds, judicious use of authorised insecticides and rotation of modes of action.

Bibliographic references

• CABI – Invasive Species Compendium – Hellula undalis.
• EPPO Global Database – Hellula undalis.
• Srinivasan, R. (2012). Insect pests of cruciferous crops and their management. Journal of Applied Entomology, 136, 337–353.
• Furlong, M. J., Wright, D. J., & Dosdall, L. M. (2013). Diamondback moth ecology and management: problems, progress, and prospects. Annual Review of Entomology, 58, 517–541.