Yellow-legged clearwing

Synanthedon vespiformis

1. Identification

• Common name: Yellow-legged clearwing
• Scientific name: Synanthedon vespiformis L.
• Order: Lepidoptera
• Family: Sesiidae

2. Pest description

• Adults resembling small wasps, with transparent wings and a narrow body.
• Black coloration with yellow bands on the abdomen and characteristic yellow legs.
• Whitish, cylindrical larvae that bore into trunks and branches.
• Xylophagous species that develops inside the wood.
• Discreet activity, often detected only by the internal damage.

3. Main hosts

• Pedunculate oak.
• Portuguese oak.
• Downy oak.
• Chestnut.
• Other hardwood broadleaf trees.

4. Symptoms and damage

• Borings and internal galleries in the trunk and branches.
• Exudation of sap and fine sawdust at the entry holes.
• Structural weakening of the branches.
• Reduced vigour and greater susceptibility to other pests.
• Progressive decline in trees with repeated attacks.

5. Biological cycle

• One generation per year.
• Oviposition in summer in cracks in the bark.
• Larvae bore into the wood and develop inside it for several months.
• Pupation inside the galleries the following spring.
• Adults emerge in late spring and early summer.

6. Monitoring

• Observation of exudation and sawdust on the trunks.
• Cutting of suspect branches to detect galleries.
• Monitoring of flights with pheromone traps.
• Assessment of the percentage of affected branches.
• Annual recording of the pest's progression in the stand.

7. Management measures

• Cultural: pruning and destruction of infested branches, improvement of canopy ventilation and proper healing of wounds.
• Biological: use of pheromones for monitoring and possible mass trapping.
• Integrated protection: interventions only when justified, judicious application of authorised insecticides and integration of cultural practices to reduce the incidence of the pest.

Bibliographic references

• EPPO Global Database – Synanthedon vespiformis.
• CABI Invasive Species Compendium – S. vespiformis.
• DGAV – Programa Operacional de Sanidade Florestal (POSF) (2019).
• DGAV – Plano de Ação Nacional para o Controlo de Pragas e Doenças Florestais (2019).
• ICNF – Technical reports on xylophagous pests of broadleaf trees (2019–2023).
• Alford, D. (2007). Pest management in fruit and forest trees.