Unusual galling on citrus—have you seen it?

Industry Update August 2007

Background of the detection

Soft galls and a swollen thorn base caused by Eurytoma.

In March 2007, samples of citrus rootstock twigs with unusual insect damage were collected from a property in the Central Burnett region of Queensland.

A single wasp reared from the infested twigs resembled the native citrus gall wasp (CGW, Bruchophagus fellis). However, the damage, symptoms and larvae were sufficiently different from CGW to raise concerns that this may be an exotic pest or a native pest not previously associated with citrus.

Wasps reared from infested twigs were identified to be from the genus Eurytoma, but the species could not be determined.

To date, damage has been noted on twigs, thorns, soft terminal growth and the bases of midribs and petioles, mainly on fieldgrown Troyer citrange rootstocks or regrowth beneath unthrifty scions.

Surveys of orchards in proximity to known detections have not revealed damage to scion material or fruit.

At present, it is not known if the wasp attacks citrus varieties commonly grown in Victoria.

Symptoms and damage

Wasp emergence hole and typical galls. Photos by Dan Papacek, Bugs for Bugs, Mundubbera.

Affected twigs have soft, raised, spherical or irregular swellings, with numerous small, white larvae inside. Affected thorns are shortened, swollen and distorted.

Unlike CGW, Eurytoma galls are not woody, the larvae do not occur in circular cells and it can complete several generations per year.

Emergence holes associated with Eurytoma wasps can be apparent at ~20cm intervals on stems in which several generations of the wasp have been completed.

Heavy infestation of soft terminal tissue causes cessation of growth, poor graft performance and production of regrowth shoots below damaged areas; the worstaffected twigs break off just below the growing point.

Summary of current situation

The Queensland Department of Primary Industries and Fisheries is working with CSIRO to identify the wasp and with citrus consultants to establish the distribution of the wasp and the varieties which it attacks.

You can help to establish the distribution of the wasp by reporting damage or symptoms on citrus similar to that shown above.