Eucalyptus gall wasp

Heavy infestations of eucalyptus gall wasp spoil the appearance of the older foliage in spring and may result in excessive leaf fall. This pest, which was first detected in Britain in 2005, is restricted to South East England but it is spreading.

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

Quick facts

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

What is eucalyptus gall wasp?

The gall wasp is a minute 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 each contains a tiny white grub. The galls are also of uniform sizeand shape 
  • Oedema growths are solid and more irregular in size and shape. The galls are most noticeable in early spring when infestations can 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

Non-chemical control

  • Collect and dispose of fallen leaves in spring as this will prevent some of the gall wasps completing their development

Chemical control

  • On tall trees, control is not possible
  • If the tree is small enough for the foliage to be sprayed thoroughly, a systemic insecticide such as thiacloprid (e.g. Bayer Provado Ultimate Bug Killer) or acetamiprid (e.g. Bug Clear Ultra) applied in late May may give some protection

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology

  • The black adult wasps are 1mm long and they emerge in late May to June
  • The identity of this gall wasp is currently uncertain but they are close to an Australian species, Ophelimus maskelli
  • Females lay eggs on new eucalyptus foliage in early summer, 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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