Chestnut gall wasp

Dryocosmus kuriphilus

1. Identification

• Common name: Chestnut gall wasp
• Scientific name: Dryocosmus kuriphilus Yasumatsu
• Order: Hymenoptera
• Family: Cynipidae

2. Pest description

• Small wasp (approx. 2.5–3 mm), black to dark-brown in coloration.
• The females are parthenogenetic, with no known males.
• Induces the formation of galls on buds, leaves and young branches of chestnut trees.
• Considered one of the most destructive pests of chestnut trees worldwide.

3. Main hosts

• European chestnut (Castanea sativa).
• Japanese chestnut (C. crenata).
• Chinese chestnut (C. mollissima).
• Hybrids of Castanea.

4. Symptoms and damage

• Formation of green to pinkish galls on buds, leaves and branches.
• Reduction in annual growth and fruit production.
• Drying of young branches and a decrease in tree vitality.
• In severe attacks, significant production losses and greater susceptibility to other pests and diseases.

5. Biological cycle

• Females emerge in summer and oviposit in buds for the following cycle.
• Larvae develop inside the tissues, inducing the formation of galls.
• Galls become visible the following spring.
• One generation per year (univoltine).
• Survives as a larva inside the galls during winter.

6. Monitoring

• Direct observation of galls on buds, leaves and young branches.
• Assessment of the percentage of affected buds.
• Annual monitoring in late spring and early summer.
• Recording of gall development throughout the season.

7. Management measures

• Cultural: removal and destruction of branches with galls before the emergence of the females; sanitary pruning.
• Preventive: use of certified, pest-free plant material; avoid the movement of infested plants.
• Biological: release of the parasitoid Torymus sinensis, widely used in biological control programmes.
• Integrated protection: integration of cultural and biological measures; continuous surveillance in orchards and stands.

Bibliographic references

• EPPO Global Database – Dryocosmus kuriphilus.
• CABI – Invasive Species Compendium – Dryocosmus kuriphilus.
• Battisti, A. et al. (2014). Biology and management of Dryocosmus kuriphilus. Forest Science.
• Moriya, S. et al. (2003). Classical biological control of the chestnut gall wasp in Japan. Entomological Science.
• Quacchia, A. et al. (2014). Torymus sinensis: a successful biological control agent against Dryocosmus kuriphilus in Europe. Biological Control.