Over The Horizon

Aussie Miner Threatens

The arrival and establishment of exotic pests and diseases pose a constant threat to New Zealand's native and exotic plants, and yet another new pest in Auckland looks likely to damage important amenity trees in the region.

Recent arrivals have largely come from Australia and include the painted apple moth (Teia anartoides), the white cedar moth (Leptocneria reducta), a eucalyptus leaf miner (Acrocercops laciniella), and most recently the banksia leaf miner (Stegommata sulfuratella). Of these, only the two leaf mining caterpillars have definitely established.

The banksia leaf miner is a tiny, pure white moth with fringes of hairs on its wings and adorned with a fluffy white "cap". It was first discovered by Forest Research's Forest Health Adviser, Chris Scott, when he noticed damage on the leaves of a coastal banksia tree, Banksia integrifolia, growing inside the hippo enclosure at Auckland Zoo.

Forest Health Advisers have the important job of regularly surveying the vegetation surrounding likely high risk areas, such as ports and airports, to pick up new arrivals.

Moths were reared from the dying leaves at Forest Research, and entomologists there recognised that this was a new insect record for New Zealand. Their identification was later confirmed by a Landcare scientist at the New Zealand Arthropod Collection in Auckland.

The coastal banksia is a fast growing evergreen tree that is native to New South Wales and Queensland. It is valued as an amenity and shelter belt tree in exposed situations because of its hardiness and salt tolerance. Its yellow flowers are also a valuable nectar source for many native New Zealand birds such as tuis and bellbirds.

This new moth is a potentially serious threat to the health of the coastal banksia, and perhaps also all the other species of banksia growing here. In Australia, it has attacked red honeysuckle banksia (Banksia serrata) and has been collected from a second species, possibly Banksia conferta, in Auckland.

Its caterpillars feed on the internal tissue of young leaves, creating a mine or tunnel, which causes the damaged part of the leaf to dry out and turn brown. A caterpillar can hollow out an entire young leaf, although on older, harder leaves the mining is limited to the tip. The ends of branches on the lower half of an infested tree can become completely brown from caterpillar feeding. These damaged leaves fall off, leaving the growing ends of the branches almost completely bare.

The leaf miner's tiny caterpillars are a pale green colour and up to 5mm long, as are the pupae. The pupae may be found held in silken hammocks strung amongst the banksia leaves. he banksia leaves.

Currently, the insects' distribution is thought to extend from Waiuku in the south, Mt Albert and Blockhouse Bay in the west, Glendene in the North, and Glendowie and Remuera in the East. The extent of the distribution, coupled with the difficulty of killing the caterpillars inside leaves has led MAF to declare that eradication is not an option. Only time will tell how much damage the leaf miner will do to these valued trees.

If you wish to check whether damage on your banksia trees has been caused by this new caterpillar, send a leaf sample in a sealed bag to Entomology, Forest Health and Biosecurity, Forest Research, PB 3020, Rotorua.

Dr Toni Withers Forest Research