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Blackbutt leafminer not as severe as suspected

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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. 93, February 2000.

Monthly monitoring of Eucalyptus pilularis trees in Auckland has revealed that the blackbutt leafminer Acrocercops laciniella has successfully over-wintered (first report FHNews 83: 1-2, March 1999). Throughout the winter small numbers of larvae were found alive within mines, although abundance was much lower than during the warmer months. The first eggs were laid in flushing foliage in late October, with a second generation appearing in late December. Examination of leafmines have failed to find any natural enemies of A. laciniella larvae, however mine failure seems to be quite high. Often mines split open before the larva is fully developed, which may result in the death of the larva. In addition, the leaf may "abort" the eggs of A. laciniella, which are laid just beneath the cuticle, by abscising the leaf tissue surrounding the egg. This causes the egg to dehydrate and fail to hatch. My observation is that the sheer vigour of the affected eucalypts is preventing A. laciniella from having a significantly detrimental impact upon growth. The crowns of these trees are still very thick, although the appearance of the trees is affected through the curled and browned appearance of mined leaves.

Toni Withers, Forest Research

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