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Asian Chestnut Gall Wasp

Dryocosmus kuriphilus[3]

The Asian chestnut gall wasp is an invasive wasp from China whose larvae turn chestnut buds into galls.[1][2]

Group
Insect
Order
Hymenoptera
Family
Cynipidae
US records
13 states
Sources
3 cited
Updated
2026-10-17
Green, red-tinged Asian chestnut gall wasp gall on a new chestnut shoot
Green, red-tinged Asian chestnut gall wasp gall on a new chestnut shoot. (c) Andy Deans, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0
On this page
  1. Identification
  2. Where it lives
  3. Biology
  4. Damage and signs
  5. Health risk
  6. Control
  7. Related profiles
  8. Common questions
  9. Sources

How to identify it

  • Look for round, greenish-red galls about 1/2 to 1 inch across on new chestnut shoots, leaf stems or leaves in spring.[2]
  • Old galls turn woody and dry and stay on the tree for years, with small leaves still attached in winter, which makes infestations easy to spot.[2]
  • Adults are tiny wasps, 2.5 to 3 mm long; only females are known.[1][2]

Where it lives

Native to China; first found in the US in Georgia in 1974, it has spread to at least 12 states east of the Mississippi, reaching Connecticut in 2011 and Massachusetts in 2012.[1][2]

US map: public records from 13 states since 1990 (GBIF).

Biology and life cycle

There is one generation a year. Females lay up to 300 eggs inside buds in early summer, and young larvae overwinter hidden in the dormant buds.[1][2]

At budbreak the larvae trigger rapid gall growth; each gall has one to several chambers, and adults emerge in early summer.[1][2]

Damage and signs

  • All chestnuts are susceptible, including American, Chinese, Japanese and European chestnut and chinquapins.[1][2]
  • Galling stunts shoots, cuts flowering and nut production and kills twigs; small trees can die when other stresses add up.[1]

Health risk

None to people or pets.[1][2]

Control

Prevention

Moving infested chestnut plants is the main way it reaches new areas, and infested buds are very hard to detect.[2]

Traps and physical control

On small trees, scout for green galls in June and prune them out before adults emerge.[1]

Biological control

Torymus sinensis, a parasitoid wasp released in the eastern US in the 1970s, follows the pest and usually keeps damage low on established trees; leave old galls late in the season so it can develop.[1][2]

Pesticides

Insecticides are ineffective, partly because the larvae are sheltered inside buds and gall tissue.[1][2]

Common questions

What are the red-green balls on my chestnut tree?
Most likely galls of the Asian chestnut gall wasp.[1][2]
Should I spray my chestnut for gall wasps?
No; sprays don't reach the larvae, and a released parasitoid wasp usually keeps the pest in check.[1][2]

Sources

  1. UMass Extension Landscape, Nursery and Urban Forestry Program (Landscape Insect & Mite Guide), “Dryocosmus kuriphilus (Asian Chestnut Gall Wasp).” www.umass.edu/agriculture-food-environment/landscape/publications-resources/insect-mite-guide/dryocosmus-kuriphilus (accessed 2026-10-16)
  2. University of Kentucky Entomology (ENTFACT), “Asian Chestnut Gall Wasp (ACGW) in Kentucky.” entomology.ca.uky.edu/entfact/asian-chestnut-gall-wasp-acgw-kentucky (accessed 2026-10-16)
  3. iNaturalist, “Dryocosmus kuriphilus taxon page (order and family).” www.inaturalist.org/taxa/357839 (accessed 2026-10-06)

Updated 2026-10-17. Built from sourced records. Spot an error? Tell us.