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Chestnut Gall Wasp

Dryocosmus kuriphilus

Chestnut Gall Wasp, Oriental Chestnut Gall Wasp, Asian Chestnut Gall Wasp

A close up of wasp larvae within a gall produced by Dryocosmus kuriphilus oak gall wasps
Parasitoïd of Dryocosmus kuriphilus (31765898760) by Gilles San Martin (CC BY-SA 2.0)
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Dryocosmus kuriphilus, or the Chestnut Gall Wasp, is a tiny, fly-like wasp. Chestnut Gall Wasps are highly specialised, they're sometimes referred to as parasitic wasps or parasitoids. They require a plant host to reproduce successfully. The female gall wasp lays eggs in the leaves of Sweet Chestnut trees, resulting in the production of pink and green fleshy galls that protrude from the veins of leaves. Invasive species can be problematic because native species are not used to their effects. Unfortunately, the presence of this wasp can weaken Sweet Chestnut trees, making them vulnerable diseases like sweet chestnut blight. This wasp was first introduced to Europe in 2002. Now, it's become established in Britain. Suspected infestations should be reported via TreeAlert so that we can learn more about this wasps distribution.
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Traits

These wasps are invasive.

Appearance

Adults: These wasps are so tiny it's unlikely you'd see them. Their presence is typically recognised by the galls produced as a result of the larval activity in plants. The gall wasp eggs and larvae remain inside the plant and gall. Dryocosmus kuriphilus is the only species that will use sweet chestnut to lay eggs. If galls are sighted in sweet chestnut trees, then it should be reported via TreeAlert.

Symptoms

Abnormal protrusions, or galls, will be evident on the leaves and branches of sweet chestnut. Infested leaves may fall prematurely.

Activity

Diurnal

Personality

Order

Hymenoptera

Family

Cynipidae

Metamorphosis

Complete

Distribution

Northern America, Asia and Europe

Biological treatment

Unfortunately, plants can't be treated for these insects. The problem with gall-forming insects is that they're concealed and protected within the plant gall. A parasitoid wasp is being trialled as a form of biocontrol in some parts of Europe. However, this is hasn't been tested in the UK.

Chemical treatment

Insecticides are unlikely to work on this wasp. Any sightings should be reported via TreeAlert.

Attracts

A close up of a green Castanea sativa plant

Sweet Chestnut

Castanea sativa

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