Oak processionary

Thaumetopoea processionea

1. Identification

• Common name: Oak processionary moth
• Scientific name: Thaumetopoea processionea L.
• Order: Lepidoptera
• Family: Notodontidae

2. Pest description

• Caterpillars with a greyish body and dark longitudinal bands.
• Covered in highly allergenic urticating hairs.
• They form silky nests on the trunks and branches of oaks.
• They move in “procession” during spring.
• Adults are small brownish moths with nocturnal flight.

3. Main hosts

• Pedunculate oak.
• Sessile oak.
• Portuguese oak.
• Other species of Quercus spp..
• Attacks are more frequent in young or weakened oak stands.

4. Symptoms and damage

• Intense defoliation in spring.
• Reduced vigour and growth of the trees.
• Greater susceptibility to other pests and diseases.
• High sanitary risk due to the urticating hairs, which cause skin, eye and respiratory irritations.
• Danger to people and animals, especially in urban and recreational areas.

5. Biological cycle

• One generation per year.
• Egg-laying in summer on thin branches of the oaks.
• Hatching at the beginning of spring.
• Formation of silky nests on the branches.
• Procession for burrowing and pupation at the end of spring.
• Adults emerge in summer.

6. Monitoring

• Observation of silky nests on the branches.
• Checking for caterpillars in procession in spring.
• Monitoring with pheromone traps to detect flights.
• Assessment of defoliation intensity.
• Identification of risk zones for people and animals.

7. Management measures

• Cultural: manual removal of nests when possible and safe destruction of the collected material.
• Biological: application of Bacillus thuringiensis at appropriate periods.
• Mechanical: installation of traps collecting the caterpillars in procession on the trunk.
• Integrated protection: monitoring with pheromones, interventions only when justified, judicious application of authorised products and proper management of risk areas.

Bibliographic references

• EPPO Global Database – Thaumetopoea processionea.
• CABI Invasive Species Compendium – T. processionea.
• DGAV – Forest Health Operational Programme (POSF) (2019).
• DGAV – National Action Plan for the Control of Forest Pests and Diseases (2019).
• ICNF – Monitoring reports on the oak processionary moth (2019–2023).
• Groenen, F. et al. (2003). Biology and impact of the oak processionary moth.