Eucalyptus gall wasp

Eucalyptus gall wasp causes small raised corky lumps on the older foliage and may result in excessive leaf fall. This minute insect was first detected in Britain in 2005 and it has spread across southern England.

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Eucalyptus gall wasp (Ophelimus maskelli) on Eucalyptus (Eucalyptus sp.). Credit: RHS/Entomology.

Quick facts

Common name Eucalyptus gall wasp
Scientific name Ophelimus maskelli
Plants affected Eucalyptus
Main symptoms Small, slightly raised swellings appear on the leaves in spring
Most active March-June

What is eucalyptus gall wasp?

Gall wasps are a group of the bees ants and wasps (Hymenoptera) that as larvae feed within plant material. They feed within altered plant growths (galls) that are a result of their presence.

The eucalyptus gall wasp is a minute (<1mm) black insect whose larvae develop inside raised galls that form on eucalyptus leaves during spring..

 

Symptoms

  • Slightly raised swellings, about 1mm in diameter, develop on either side of eucalyptus leaves
  • These pinkish-brown galls can be mistaken for a physiological disorder known as oedema, but the galls are hollow and in spring and early summer each contains a tiny white grub. The galls are of uniform size and shape 
  • Oedema growths are solid and more irregular in size and shape
  • The galls are most noticeable in early spring when it can occasionally cause heavy leaf fall

Control

The gall wasp does not affect the long term health or vigour of the tree, but can affect its appearance. Its presence must be tolerated and insecticides are unlikely to give control. 

Collecting and disposing of fallen leaves in spring may prevent some of the gall wasps completing their development.

Biology

  • The black adult wasps are 1mm long and they emerge in late May to June
  • Females lay eggs on new eucalyptus foliage in spring, and the larvae develop within the leaves, although the raised galls do not become particularly obvious until the following spring, when the mature larvae pupate within the galls

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