Farm Forestry New Zealand

PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND

New Eucalypt insect found in Auckland

Scion is the leading provider of forest-related knowledge in New Zealand
Formerly known as the Forest Research Institute, Scion has been a leader in research relating to forest health for over 50 years. The Rotorua-based Crown Research Institute continues to provide science that will protect all forests from damage caused by insect pests, pathogens and weeds. The information presented below arises from these research activities.

From Forest Health News No. 83, March 1999.

MAF Forest Health Adviser, Chris Scott, while undertaking a routine Port Environs survey on the Aviation Golf Course, Mangere, in January 1999 observed some leaf mines on Eucalyptus leucoxylon. The mines differed slightly in appearance from those of Phylacteophaga froggatti (leaf blister sawfly) and samples were sent to Forest Research. Entomologists at Forest Research identified the mining insect as a species of Acrocercops not previously recorded in New Zealand. Specimens were sent to Dr Robert Hoare, Landcare Research, who identified it as A. laciniella (Meyrick), a Gracillarid moth, commonly known as the blackbutt leafminer. Further explorations were made by Chris Scott and additional infestations found on E. leucoxylon, E. viminalis and E. macarthurii in the Auckland suburbs of Mangere, Meadowbank, Mt Albert, Glendowie and Devonport, and on E. botryoides in Greenlane. Given the insects present distribution in Auckland MAF decided that it was already too firmly established for an eradication attempt.

In Australia Acrocercops laciniella is widespread from southern Queensland to Tasmania. Its main host is believed to be E. pilularis , and it has periodically caused severe damage to E. pilularis, particularly between July and September, in coastal NSW (Elliot, 1998). The insect attacks both mature and coppice foliage destroying all green tissue in the leaves, causing them to curl and giving the tree a burnt appearance (Moore, 1963). The damaged trees regrew their foliage within 3 months and appeared to recover. Acrocercops laciniella has also been commonly reared from mines on Angophora floribunda, A. costata, and E. saligna . In Tasmania it is common on the juvenile foliage of E. nitens, E. globulus, E. regnans, and E. obliqua (D. Bashford, pers. comm.). More recent host records from eastern Australia  include:  E. viminalis, E. acmenoides, E. dives, E. bridgesiana, E. rossii, E. globulus ssp. pseudoglobulus , and E. macrorhyncha (M. Horak, pers. comm.; Moore, 1966).

Adult moths are very small and pale brown (up to 9 mm). Eggs are deposited within the leaf. Young larvae begin mining within the leaf in a small narrow pattern, which as they grow forms a large blotch-shaped mine and causes the leaf cuticle to blister. A characteristic that differentiates blackbutt leafminer mines from leaf blister sawfly mines, is the presence of a dark stain against one edge of the mine caused by the liquid excreta from the feeding larva. Several mines may coalesce on a single leaf and contain more than one larva, resulting in mines of considerable variation in size. When the larva exits the mine to pupate, it cuts a tiny semicircular slit in the leaf cuticle and falls to the ground.

In Australia a number of parasitoids of Acrocercops laciniella, including Braconid and Chalcidoid wasps, have been reared from its leafmines (D. Bashford, pers. comm.). Already present on Acacia melanoxylon in New Zealand is Acrocercops alysidota which is parasitised by the eulophids Diaulomorpha sp. and Cirrospilus sp. (Appleton, 1998). The host range of these parasitoids is currently being investigated by Forest Research. It is too soon to make predictions of the potential pest status of this latest insect to establish on eucalypts in New Zealand. However we recommend strongly that infested foliage not be transported out of the Auckland region. Also samples being sent to Forest Research for identification should be tightly sealed and labelled "Open under Quarantine".

Toni Withers, Forest Research

References

Appleton, C. (1998): Parasites of the leaf miner Acrocercops alysidota (Lepidoptera: Gracillaridae). TheWeta 21:20-21.
Elliot, H.J.; Ohmart, C.P.; Wylie, F.R. (1998): "Insect Pests of Australian Forests; Ecology and Management". Inkata Press, Melbourne.
Moore,   K.M.   (1963): Two species of lepidopterous leafminers attacking Eucalyptus pilularis Smith. Australian Zoologist 13 :46-53.
Moore, K.M. (1966): Observations on some Australian forest insects, 22. Notes on some Australian leaf-miners. Australian Zoologist 13 : 303-349.

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(Scion is the trading name of the New Zealand Forest Research Institute Limited.)