Eucalyptus gall wasp

Infestations of eucalyptus gall wasp can spoil the appearance of 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.

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

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 appear on the leaves in spring
Most active March-June

What is eucalyptus gall wasp?

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 infestations 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 largely be tolerated and insecticides are unlikely to give good 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
  • 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 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


Gardeners' calendar

Advice from the RHS

Find out what to do this month with our gardeners' calendar

Advice from the RHS

Did you find the advice you needed?

RHS members can get exclusive individual advice from the RHS Gardening Advice team.

Join the RHS now

Get involved

We're a UK charity established to share the best in gardening. We want to enrich everyone's life through plants, and make the UK a greener and more beautiful place.