Date: 03 October, 2011

Beware Poisonous Insect, Northlanders Urged

Officials hope to eventually release a parasitic wasp to target an unwanted Aussie invader recently discovered in Whangarei – and whose caterpillar stage has poisonous spines that can deliver painful stings.

But such a release could be 12 months away and until then, experts are asking Northlanders coming across any Gum Leaf Skeletoniser to give them a wide berth – but report any sightings to the Northland Regional Council on (0800) 002 004.

The council was informed recently by MAF officials that the Gum Leaf Skeletoniser had been found several weeks ago at a port in the Whangarei area through MAF's high risk site surveillance programme.

Don McKenzie, the council’s Biosecurity Senior Programme Manager, says the insect– which damages gum trees by eating their leaves – has been in the greater Auckland area for about a decade, but is not thought to have been in Northland until now. Previously, it had only been recorded as far north as the Warkworth area.

Although it favours eucalypts, Gum Leaf Skeletoniser also thrives on silver birch and can damage some oak, copper beech and plum.

“It’s not only a nasty forestry pest but will affect eucalypt trees in home gardens, parks and reserves and schools.”

Mr McKenzie says fortunately, it’s not generally attracted to our native plants, although it can feed on them when they’re growing very close to eucalypts.

“In these rare cases, they don’t usually cause significant damage and typically, most larvae hatching on to native plant leaves die within two weeks or will try to move away to find a better host plant.”

However, Mr McKenzie says aside from the damage the insects pose to trees, they are also a problem in their caterpillar stage during which they are covered in an impressive array of poisonous, stinging spines that can affect humans.

“The spines are stiff and hollow and the venom in them can be injected into skin on contact (even if the insect is dead) causing severe pain, itchy welts and a reaction that can last for days.”

MAF Biosecurity New Zealand advises affected people to apply ice packs to the exposed area and that antihistamine creams can be beneficial in recovering from sting symptoms.

However, they say if symptoms develop beyond the immediate sting area (like a widespread rash, shortness of breath or collapse) an ambulance should be called immediately.

If a Gum Leaf Skeletoniser caterpillar is eaten – especially by a child – medical attention needs to be sought immediately. If the insect comes into contact with an eye, the area needs to be washed thoroughly and again, medical help sought.

Mr McKenzie says the regional council recognised the insect as a potential risk to Northland some time ago and has been helping to fund the breeding of a host-specific parasitic wasp to target it.

Cable Bay, Northland-based entomologist Dr Jenny Dymock says those wasps are currently being bred in Auckland, however, it could be up to a year before there are enough available for release here.

Dr Dymock, who is contracted by the Northland Regional Council, says in the meantime Northlanders should be vigilant for the pest which goes through four very different looking life stages.

“It’s also very important to avoid transporting bark and leaf material, especially over the next couple of months and again in February/March when pupae will be living in them. A small amount of vigilance now could save Northland huge amounts in the future.”

Dr Dymock says eggs are about 1 mm in diameter and are laid in groups 100-200 in parallel rows on young leaves. The eggs are yellow-green at first, turning brown as they develop.

Caterpillars are hairy and 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 while moths are dull grey with silver-grey forewings and a wingspan of 20-30mm.
Dr Dymock says two life cycles are completed annually, one in summer and one winter.

She says a booklet, factsheet and series of frequently asked questions about Gum Leaf Skeletoniser’s health effects and management is available online at: http://www.biosecurity.govt.nz/pests/gum-leaf-skeletoniser
Mr McKenzie says information about the pest (including a booklet) is also available from Northland Regional Council offices.

Dr Dymock says in plantation forestry areas the insects can be sprayed, but the chemicals have to come into contact with the insect to kill them.

“In urban areas where spraying is not appropriate, individual trees can be treated using an insecticide injected directly into the tree’s stem. It’s transported to the leaves via sap, where it is ingested by insects feeding on the leaves.”

Mr McKenzie says Northlanders wanting advice on Gum Leaf Skeletoniser management, especially on spray or tree stem injection control methods, should contact Scion Forest Protection at the New Zealand Forest Research Institute Ltd in Rotorua (07) 343 5899 or email: enquiries@scionresearch.com

ENDS

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