Dryocosmus kuriphilus
Dryocosmus kuriphilus Yasumatsu - Chestnut Gall Wasp
Identity
Name:
Dryocosmus kuriphilus
Yasumatsu
Taxonomic position:
Insecta: Hymenoptera: Cynipidae
Host
D. kuriphilus
attacks Castanea crenata
(Japanese chestnut), Castanea dentata
(American chestnut), Castanea mollissima
(Chinese chestnut), Castanea sativa
(European chestnut) and their hybrids. It infests also Castanea seguinii
in China, but is not known to attack the wild North American species Castanea pumila
and Castanea alnifolia, which are very often grown adjacent to infested chestnuts.
Biology
D. kuriphilus
is a univoltine species, reproducing parthenogenetically. Early instar larvae overwinter inside chestnut buds. At the time of bud burst in spring, the adults emerge to induce the formation of 5-20 mm green or rose-coloured galls, which develop in mid-April on new shoots. The larvae feed 20-30 days within the galls before pupating. Depending on locality (altitude, exposure) and chestnut cultivar, pupation occurs from mid-May until the end of July. Individuals are all females (males of this species have never been collected). The famales lay 3-5 eggs per cluster inside buds (they can lay over 100 eggs and some buds contain 20-30 eggs). The female lifetime is about 10 days and some of which is spent boring a tunnel to emerge from the gall. The eggs hatch in 30-40 days. Larval growth then proceeds very slow through the autumn and winter.
Detection and Identification
Symptoms: galls are unilocular or multilocular, 5-20 mm in diameter, green or rose-coloured, often containing of developing leaves, stems and petioles. They develop on young twigs, on leaf petioles or on the midrib of the leaves. After adult emergence, the gall dries, becomes wood-like, and remains attached to the tree for up to two years. While galls are readily detected on plants or part of plants, eggs or first instar larvae inside the buds cannot be detected by simple visual inspections.
Morphology: D. kuriphilus
eggs are deposited by females into the buds of current shoots in June and July. Eggs are oval, milky white, 0.1-0.2 mm long, with a long stalk. The larva of D. kutiphilus
is 2.5 mm long when fully grown, milky white, without eyes and legs. The pupa is 2.5 mm long, black or dark brown. The adult female is 2.5-3 mm long on average and its body is black; legs, scapus and pedicels of antennae, apex of clypeus and mandibles are yellow brown; head is finely sculptured; scutum, mesopleuron and gaster are highly polished and smooth; propodeum with 3 distinct longitudinal carinae; propodeum, pronotum (especially above) strongly sculptured; scutum with 2 uniformly impressed and pitted grooves (notaulices) that coverage posteriorly; radial cell of forewing opened; antennae 14-segmented with apical segments not expanded into a club. The adult female most closely resembles the European oak, but in D. kuriphilus
vertex is black, antennae 14-segmented and propodeum with distinct median longitudinal carina.
a) Adult and pupa of D. kuriphilus on sectioned gall (Source Piedmont Region); b) Grafic particular of D. kuriphilus
(Source Ditxon et al., 1986); c) Adult of D. kuriphilus
(Source Actaplantorum)
a) D. kuriphilus
eggs (Source Piedmont Region); b) Larval stage of D. kuriphilus
on sectioned gall (Source Piedmont Region); c) D. kuriphilus
larva inside gall (Source EPPO, 2005)
Pathway for movement
Spread of D. kuriphilus
into new countries occurs by introduction of infested twigs or shoots. Local spread occurs through the movement of infested twigs and young plants, or by flight of the adult females during the period (end of May to the end of July) when they are present.
Pest significance
Economic impact: By attacking the vegetative buds and forming a gall, D. kuriphilus disrupts twig growth and reduces fruiting. Commercial growers may expect yield reductions of 50–70%. Severe infestations may result in the decline and death of chestnut trees. D. kuriphilus
is the most severe insect pest worldwide on chestnuts and can eliminate nut production and even kill trees (Dixon et al., 1986). Where chestnut is planted in Europe for timber and to stabilize slopes, D. kuriphilus
could cause serious decline.
Control: Infestations in small chestnut orchards may be reduced by pruning and destroying the infested shoots, but commercial growers cannot rely on this strategy because of the cost. Persistent insecticides may prove effective against females and young larvae, but side-effects on the environment could be serious. D. kuriphilus
can be effectively controlled by natual enemies, particularly hymenopteran parasitoids. T. sinensis
is the most efficient biological control agent for D. kuriphilus
and appears to be very effective in mass-release program (Moriya et al., 2002).
World Alocton and Autocton Distribution of Dryocosmus kuriphilus
(Source Nieves-Aldrey, Tapetado, 2015)
References
- Actaplantorum www.actaplantorum.org
- European and Mediterranean Plant Protection Organization Bulletin (2005), Data sheet on quarantine pests - Dryocosmus kuriphilus, OEPP/EPPO, Bulletin 35, 422-424
- Dixon WN, Burns RE Stange LA (1986), Oriental chestnut gall wasp. Dryocosmus kuriphilus, Entomology Circular no. 287, 1-2. Division of Plant Industry. Florida Department of Agriculture & Consumer Services, Gainsville (US)
- Moriya S, Shiga M & Adachi I (2002), Classical biological control of chestnut gall wasp in Japan. Proceedings of the 1st International Symposium on Biological Control of Arthropods. University of Hawaii, Waikiki (US)
- Nieves-Aldrey J. L., Tapetado D. G. (2015), Evaluación de posible impacto ambiental del uso de Torymus sinensis como controlador biológico de la plaga de la avispa del castaño, Dryocosmus kuriphilus Yasumatsu en España, BioCastanea 2015
- Piedmont Region Italy www.regione.piemonte.it
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