Advice

RHS Help & Advice

Eucalyptus gall wasp

This pest was first detected in Britain in 2005.

Symptoms

Slightly raised swellings, about 1mm in diameter, develop on either side of eucalyptus leaves. These pinkish-brown galls can be mistaken for oedema, but they are hollow and each contains a tiny grub. The galls are most noticeable in early spring when infestations can cause heavy leaf fall. At present this pest is restricted to the London area but is spreading.

Biology

The black adult wasps emerge in late May to June. Their identity is uncertain but they are close to an Australian species Ophelimus maskelli. Females lay eggs on new eucalyptus foliage in early summer, and mature larvae pupate within the galls in the following spring.

Control

On tall trees, control is difficult; spraying those small enough with the systemic insecticide imidacloprid or thiacloprid (Provado Ultimate Bug Killer, concentrate or ready to use) in late May may give some protection.

Collect and dispose of fallen leaves as this will help give some control.