Dryocosmus kuriphilus

Dryocosmus kuriphilus is a species of gall wasp known by the common names chestnut gall wasp, Oriental chestnut gall wasp, and Asian chestnut gall wasp. It is native to China and it is known in many other parts of the world, particularly the Northern Hemisphere, as an introduced species and an invasive horticultural pest. It attacks many species of chestnut (genus Castanea), including most cultivated varieties. It is considered the world's worst pest of chestnuts.[1]

Dryocosmus kuriphilus
Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Class:
Insecta
Order:
Hymenoptera
Suborder:
Apocrita
Superfamily:
Cynipoidea
Family:
Cynipidae
Genus:
Dryocosmus
Species:
D. kuriphilus
Binomial name
Dryocosmus kuriphilus
Yasumatsu, 1951
Galls caused by Dryocosmus kuriphilus on sweet chestnut

When it was first discovered, the wasp was considered to be a species of Biorhiza. It was given its current name in 1951, when it was formally described.[2] By this time it had invaded Japan and was attacking chestnuts there.[3] It is now in Korea, Nepal,[4] Italy, Slovenia,[5] France,[6] Switzerland[7] and other parts of Europe, and the southeastern United States.[2]

The adult female wasp is 2.5 to 3 millimeters long and shiny black in color with brown legs. It produces stalked white eggs, each about 0.2 millimeters long, and the larva is white and about 2.5 millimeters long. The adult male of the species has never been observed.[2]

The female lays eggs in the buds of chestnut trees, sometimes producing over 100 eggs.[2] The wasp is thelytokous, producing fertile eggs by parthenogenesis, without fertilization by a male. Oviposition occurs in the summer. Larvae hatch from the eggs but do not begin growing immediately. Their growth begins the following spring, when the tree buds begin to develop. At this time, the larvae induce the formation of galls on the tree.[8] The galls are green or pinkish and up to 2 centimeters wide.[2] The larvae develop inside the protective gall structures and emerge from them as adults. The galls dry out and become woody. The galls can be very damaging to the tree.[8] They occur on the new growth of the tree, disrupting the fruiting process, and can reduce a tree's yield up to 70%. They are even known to kill trees.[1]

The presence of galls can also increase the likelihood of the tree's becoming infected with chestnut blight, a condition caused by the fungus Cryphonectria parasitica. The opened gall left by the wasp after it matures and departs may be an entrance through which the fungus can infest the tree's tissues.[7] The galls can also become infected by the sweet chestnut pathogen Gnomoniopsis smithogilvyi.[9]

Chestnut species affected by the gall wasp include Japanese chestnut (Castanea crenata), American chestnut (C. dentata), Chinese chestnut (C. mollissima), European chestnut (C. sativa), Seguin chestnut (C. seguinii), Henry's chinquapin (C. henryi),[10] and hybrids. So far it has not been observed on the Allegheny chinquapin (C. pumila).[2]

The wasp can fly, but it is distributed to new territory more often by human activity,[10] such as the planting of new trees and the transport of infested wood.[5]

Control measures include pruning infested buds off of trees and protecting buds with netting. These methods are not practical for large numbers of trees, such as commercial orchards. In China, with lower labor costs, Chinese chinquapin (Castanea seguinii) is used as a trap crop. By planting a hedge of C. seguinii around C. mollissima (Chinese chestnut) orchards, the wasps will first encounter and attack the buds of the less valuable C. seguinii, allowing the galled twigs to be cut off and destroyed.[11] Pesticides are generally not effective because the insects take cover inside the galls.[10] One gall wasp control method which has been successful is the introduction of the torymid wasp Torymus sinensis. This parasitoid is used as an agent of biological pest control against the gall wasp in Japan. Research is underway to determine where else it might be appropriate to release the parasitoid.[12][13] A number of other parasitoids have been noted with the gall wasp, including the torymids Torymus beneficus, T. geranii, and Megastigmus nipponicus, the ormyrid wasps Ormyris punctiger and O. flavitibialis, and the eurytomid wasps Eurytoma brunniventris and E. setigera. These species do not make effective control agents, as their rates of parasitism are not high.[14]

References
  1. CABI, 2013. Dryocosmus kuriphilus. In: Invasive Species Compendium. Wallingford, UK: CAB International.
  2. Dryocosmus kuriphilus. Archived June 4, 2015, at the Wayback Machine Data Sheets on Quarantine Pests. European and Mediterranean Plant Protection Organization. 2005.
  3. Murakami, Y. A history of studies on the chestnut gall wasp in Japan. Archived 2016-03-04 at the Wayback Machine A Global Serious Pest of Chestnut Trees: Yesterday, Today and Tomorrow. Japan-Italy Joint International Symposium. November 24–25, 2009.
  4. Grazioli, I. and F. Santi. (2008). Chestnut gall wasp (Dryocosmus kuriphilus): spreading in Italy and new records in Bologna province. Bulletin of Insectology 61(2) 343-48.
  5. Chestnut gall wasp (Dryocosmus kuriphilus Yasumatsu): New harmful organism of chestnut is spreading. Phytosanitary Administration of the Republic of Slovenia. January 13, 2011.
  6. EFSA Panel on Plant Health. (2010). Risk assessment of the oriental chestnut gall wasp, Dryocosmus kuriphilus for the EU territory and identification and evaluation of risk management options. EFSA Journal 8(6) 1619.
  7. Prospero, S. and B. Forster. (2011). Chestnut gall wasp (Dryocosmus kuriphilus) infestations: new opportunities for the chestnut blight fungus Cryphonectria parasitica? New Disease Reports 23, 35.
  8. Cooper, W. R. and L. K. Rieske. (2007). Community associates of an exotic gallmaker, Dryocosmus kuriphilus (Hymenoptera: Cynipidae), in Eastern North America. Ann Entomol Soc Am 100(2) 236-44.
  9. Lione, Guglielmo; Giordano, Luana; Ferracini, Chiara; Alma, Alberto; Gonthier, Paolo (2016). "Testing ecological interactions between Gnomoniopsis castaneae and Dryocosmus kuriphilus". Acta Oecologica. 77: 10–17. doi:10.1016/j.actao.2016.08.008. ISSN 1146-609X.
  10. Bernardo, U., et al. (2013). Biology and monitoring of Dryocosmus kuriphilus on Castanea sativa in Southern Italy. Agriculture and Forest Entomology 15(1) 65-76.
  11. Janick, Jules (24 March 1992). Horticultural Reviews. ISBN 9780471574996.
  12. Quacchia, A., et al. (2008). Rearing, release and settlement prospect in Italy of Torymus sinensis, the biological control agent of the chestnut gall wasp Dryocosmus kuriphilus. BioControl 53 829-39.
  13. Gibbs, M., et al. (2011). Torymus sinensis: a viable management option for the biological control of Dryocosmus kuriphilus in Europe? BioControl 56 527-38.
  14. Moriya, S., et al. Classical biological control of the chestnut gall wasp in Japan. Archived November 21, 2010, at the Wayback Machine 1st International Symposium on Biological Control of Arthropods. Honolulu, Hawaii, USA, January 14–18, 2002.
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