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Oak Gall Wasp

Biorhiza spp.

Oak Gall Wasp, Gall Wasp

A close up of an apple gall produced by a oak gall wasp belonging to the Biorhiza genus
Biorhiza pallida 2006.05.14 14.50.54-p5140193 by Michael Becker (CC-BY-SA-3.0)
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Oak Gall Wasps are tiny gall-forming insects that belong to a highly specialised group of wasps, sometimes referred to as parasitoids. Gall wasps need a plant host to survive. However, the damage they cause is never detrimental to the plant. A gall can take many forms and looks like an abnormal growth. Gall Wasp eggs are laid in the shoot tips of new leaves in Oak. Plants begin to rapidly-produce cells, and growth becomes malformed. This particular genus is well-known for its Oak apple galls, which look a lot like apples! Each Apple Gall contains numerous chambers concealing the wasp larvae.
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Traits

Wasps cause host plant to produce abnormal growths, known as galls.
Galling activity doesn't permanently damage hosts.

Appearance

Adults: Adult wasps are sometimes compared to ants due to their small size and black-brown colouration; some are even wingless! They're tiny so it's unlikely you'd see them. Wasps are normally identified by the galls produced on the infested plant. The gall wasp eggs and larvae remain inside the plant and gall. Galls: This genus of gall wasp is best recognised from the 'apple galls' produced by some species when in oak. These look like apples, are typically attached to the underside of oak leaves and are spongy in texture. They begin looking pinky-green but will eventually dry out once larvae emerge, turning brown. Dried out galls are often found covered in numerous emergence holes where matured larvae have left the gall.

Symptoms

Squidgey, apple-like tumours may be evident underneath oak leaves or in areas of new growth. Some years tree crops can be low.

Activity

Diurnal

Personality

Order

Hymenoptera

Family

Cynipidae

Metamorphosis

Complete

Distribution

Worldwide

Biological treatment

This wasp will not impact the longterm yield of trees, but the galls it produces may be unsightly. Gall wasps seem to be more frequent in some years than others, so trees typically have quieter periods in which they recover.

Chemical treatment

Insecticides are unlikely to work on this wasp.

Attracts

Oak

Quercus spp.

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