Forest Pest Insects in North America: a Photographic Guide

Asian chestnut gall wasp

Drycosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae)

Orientation to pest

The Asian chestnut gall wasp, Drycosmus kuriphilus Yasumatsu, is a gall making cynipid that is specific to chestnut (Castanea spp.). The gall wasp is native to China but invasive in many countries around the world, including parts of the USA. Galling disrupts shoot and twig growth, impedes normal flowering, and weakens infested trees. Adult females (there are no males) emerge from galls in early-to-mid summer and lay several eggs in each chestnut bud they attack. Eggs hatch in mid-to-late summer, and young larvae feed a little and then overwinter in the infested buds. When buds begin to grow in spring, galls are formed. Galls have one to several chambers, each with a developing gall wasp larva. Larvae eat the tissue within the galls and pupate there. New gall wasps emerge soon after. After adults emerge, galls turn brown and woody and may remain on the tree for several years and are a clear sign of infestation. In China, pest outbreaks occur about every 10 years and last 2-3 years. There is one generation per year.

Hosts commonly attacked

This species is specific to species of chestnuts (Castanea).

Distribution

Asian chestnut gall wasp is native to China, but is also present in Korea, Japan, Nepal, Europe (Italy, France, Slovenia, Hungary, Switzerland, and Croatia) and the USA as an invasive pest.

Distribution of the chestnut gall wasp in the United States Ignazio Graziosi 768x512
Figure 1. Distribution of the chestnut gall wasp in the United States

Images of Asian chestnut gall wasp

Adult of Asian chestnut gall wasp Jerry Payne 768x512
Young gall of Asian chestnut gall wasp in spring Lynne Rieske 768x512
Old gall after wasp emergence Lynne Rieske 768x512
Figure 2. Adult of Asian chestnut gall wasp, Drycosmus kuriphilus Figure 3. Young gall of Asian chestnut gall wasp in spring (left) and old gall after wasp emergence (right), which may remain on trees for several years
Interior view of gall in cross section, showing multiple chambers and a one gall wasp pupa Melanie Sprinkle, Bugwood.org 768x512
View of old galls on leafless chestnut tree in winter Lynne Rieske 768x512
Figure 4. Interior view of gall in cross section, showing multiple chambers and a one gall wasp pupa Figure 5. View of old galls on leafless chestnut tree in winter

Important biological control agents related to this pest species

Classical biological control programs focusing on the parasitoid Torymus sinensis Kamijo (Hymenoptera: Torymidae) have been implemented in several countries, including Japan and the United States. Several native species also utilize the gall wasp as a host.

Web links for information on Asian chestnut gall wasp

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