Gum Leaf Skeletoniser

Uraba lugens

Gum Leaf Skeletoniser

Gum Leaf Skeletoniser

Legal Status: Notifiable Organism
Status in New Zealand: Controlled
Organism: Insects, worms and other land invertebrates

Gum leaf skeletoniser (Uraba lugens) is a native Australian moth, first discovered in New Zealand in 1992 at Mount Maunganui. This first population was eradicated, but it was found again in Auckland in 2001. Gum leaf skeletoniser is widespread in the greater Auckland region, and has now been recorded in the Waikato, Coromandel, Bay of Plenty, Napier and Nelson regions.

This pest has the potential to spread through much of the country.

Gum leaf skeletoniser is a pest in both Australia and New Zealand, mainly because of the damage it causes to gum (Eucalyptus) trees. The caterpillars have poisonous spines which can sting.

In January 2010 a biological control agent was released in Auckland to help control the pest. The agent is a parasitic wasp (Cotesia urabae) that specifically targets gum leaf skeletoniser caterpillars.

Frequently Asked Questions

Is it dangerous?

The gum leaf skeletoniser caterpillar is covered with protective spines that sting and may cause irritation. The stiff spines are hollow and contain venom, which can be injected into the human skin upon contact. This often results in local pain (sometimes severe) and welts (swollen patches on the skin) that tend to become itchy. The reaction to gum leaf skeletoniser may last for many days. Note that the spines of dead caterpillars or on shed skin retain their ability to sting.

In case of reaction to gum leaf skeletoniser caterpillars, the following first aid is advisable:

  1. Apply ice packs to the exposed area.
  2. In case of eye contact, wash area thoroughly and seek medical attention.
  3. If ingestion of caterpillar occurs, seek medical attention immediately.
  4. If symptoms develop beyond the immediate area of the sting (e.g. widespread rash, shortness of breath or collapse) call an ambulance straight away.

Biosecurity NZ has prepared fact sheets providing more specific public health information:

For further information, see Derraik JGB. 2006. Erucism in New Zealand: exposure to gum leaf skeletoniser (Uraba lugens) caterpillars in the differential diagnosis of contact dermatitis in the Auckland region. New Zealand Medical Journal 119 (1241) (offsite link to www.nzma.org.nz)

What damage can it do to trees?

Gum Leaf Skeletoniser Caterpillar
Caterpillar

Gum leaf skeletoniser caterpillars damage gum trees as they feed on their leaves. The moth's name derives from the young caterpillar's feeding habits. When young caterpillars feed they 'skeletonise' gum leaves by eating the softer parts of leaves, avoiding the veins. Older larvae are capable of eating whole leaves thus increasing damage. This damage can slow tree growth or, in severe cases, even kill younger trees.

Despite its reputation as a eucalypt specialist, gumleaf skeletoniser can also live successfully on other related Australian trees. For more details on its likely impact, see the Factsheet (offsite link to www.mpi.govt.nz).

Gum leaf skeletoniser is found in sub-tropical, Mediterranean, and temperate climates in Australia indicating that it could also be capable of surviving throughout New Zealand, with the exception of alpine areas.

What does gum leaf skeletoniser look like?

Gum leaf skeletoniser goes through four different life stages, each looking very different from the other:

Gum Leaf Skeletoniser Moth
Moth

  • Eggs are about 1 mm in diameter and are laid in groups of 100 to 200 in parallel rows on young leaves. The eggs are yellow-green at first and turn brown as they develop.
  • Caterpillars are hairy and coloured pale yellow with black and grey markings. Older caterpillars have a distinctive 'hat' on their heads.
  • Cocoons are usually formed under bark or in leaf litter and are rarely seen.
  • Moths are dull grey with silver-grey forewings and a wingspan of 20-30mm.

Two gum leaf skeletoniser life cycles are completed each year, one in summer and one in winter. For more information on the biology of this insect, see the Uraba lugens Factsheet Link to PDF document.

Chemical Control Options

How can you protect your trees?

If gum leaf skeletoniser is present in your area, signs of chewing damage will become visible when the larvae are feeding. This is most likely between the months of January-March and May-October. Chemical control methods can be used to manage the pest.

Stem injection

In urban areas where spraying is not appropriate, individual trees can be treated using stem injection methods. An insecticide injected directly into the stem is transported rapidly to the leaves through the sap of the tree, where it is ingested by insects feeding on the leaves.

Stem injection of individual trees has proven to be a safe and highly effective method of achieving prolonged protection. Researchers have determined that the insecticides acephate and methamidophos are effective in the control of gum leaf skeletoniser on trees by direct stem injection.

Both the above insecticides are systemic organophosphate insecticides that are rapidly transported through the tree's vascular system. They can remain active within the tree for months. The active period is determined by tree phenology, active ingredient and injected rates. Although these products are formulated and registered for spray applications, research has shown that they can be successfully injected into the stem using standard chemical injection apparatus.

Techniques for stem injection are still under investigation, so manufacturers' recommendations are currently unavailable.

Pesticide sprays

In plantation forestry areas, spraying with Btk, Spinosad or synthetic pyrethroids will provide effective control.

Btk stands for Bacillus thuringiensis var. kurstaki, which are naturally occurring bacteria. When used at the recommended rates for lepidopteran (such as moths) control, Btk will kill a limited range of insects, including gum leaf skeletoniser. Young larvae are the most susceptible to Btk, therefore it should be applied when the caterpillars are small in January or May/June.

Broader spectrum control can be achieved using a synthetic pythrethroid, such as deltamethrin. Like Btk, these chemicals must contact the insect in order to kill them, so the timing and deposition of the spray operations are critical to achieve maximum effect.

For advice on how to control gum leaf skeletoniser contact Stefan Gous at Scion (07 343 5518, email stefan.gous@scionresearch.com).

Page last updated: 18 March 2013