‘Acrocercops’ leucocyma (Meyrick, 1889)
Gracilaria leucocyma Meyrick, 1889
Macarostola leucocyma (Meyrick, 1889)
Parectopa leucocyma (Meyrick, 1889)
This moth is not related to true Acrocercops. Hence the apostrophes around the genus name.
Biostatus and distribution
This endemic moth is found in the northern half of the North Island where its endemic host plant, kauri, Agathis australis (Araucariaceae), occurs. It is found in native ecosystems, parks and gardens.
The moth was first named and described in 1889. It was not until 1958 that it was discovered to be a leafminer of kauri when it was reared by Keith Wise.
Conservation status: Restricted to its host plant, kauri, not threatened.
Life stages and annual cycle
There is one generation a year. Moths emerge in spring (November) and summer (February). After mating females lay eggs singly on young kauri leaves. The caterpillars form mines in leaves and when almost fully grown, induce a gall at the base of the leaf in which they spend the winter. In spring they leave the gall and make a cocoon on leaves or other suitable places in which they pupate. The annual cycle was first elucidated and described in 1962 by Keith Wise, an entomologist working for Plant Diseases Division of DSIR.
Adult moths are long and narrow at rest and about 5-6 mm long. The moth holds its wings roof-like over its body. The moth has grey forewings with white markings. Its three pairs legs are dark grey with white rings. It has a pair of very long antennae. It is presumed that the adult male and female moths are attracted to each other and mate. The female moth then lays eggs.
Caterpillars and leaf mines
Eggs are laid singly on the upper surface of new season leaves and have a shiny shell. The caterpillar hatches from an egg and tunnels directly into the leaf forming a mine just under the epidermis (skin) of the leaf. The mine is initially serpentine, but eventually it runs close to the edge of the leaf to the leaf base. Just before reaching the leaf base (petiole) the mine goes deeper into the mid vein area of the leaf. It’s feeding induces a gall, a thickening of plant tissue, in which the caterpillar makes a central cavity. The caterpillar stops feeding until spring, that is it enters a resting stage, diapause. When the caterpillar is feeding and growing, it moults (changes skin). When fully grown the caterpillar is about 4-5 mm long. The caterpillar is white and has a flat brown head with protruding jaws in front. It uses the jaws to bite off pieces of stem tissue at the edges of the leaf mine and gall. The caterpillar in the mine feeds mainly on the sap (juice) from plant cells and ingests little solid material. The mine contains the black frass (insect faeces). The caterpillar is legless and the prominent segments of the body assist the caterpillar when it moves through its mine.
In spring the caterpillar resumes feeding and consumes the inner walls of the gall, then chews a round hole in the roof of the gall through which it leaves.
Cocoon and pupa
After exiting the leaf gall the caterpillar makes a thin, silk shelter on the upper side of a kauri leaf or leaf of another plant. This silk shelter can be difficult to see. Under this shelter the caterpillar spins a silk -lined chamber (cocoon) in which it moults into a white pupa. Shortly before moth emergence, the colour of the wings and legs can be seen through the skin of the pupa. At the apex of the head of the pupa is a sharp spike. This is used by the pupa to break through one end of the cocoon. When the moth is ready to emerge, the pupa wriggles forwards, makes a hole in the cocoon and wriggles most of the way out. The hind end of the pupa grips the silk cocoon and then the moth pulls itself from the pupa.
Moths of this leafminer are similar in appearance to other moths in the genus ‘Acrocercops’, which are also leafminers. The kauri leafminer can be distinguished by the grey and white pattern on the forewings.
The kauri leafminer is the only insect forming a mine in green leaves of kauri. Hence the presence of the moth in an area can be recognised by the occurrence of its leaf mine.
In spring, mature caterpillars make their cocoons on the upper side of kauri leaves or of other plants under kauri trees. The presence of these shiny cocoons is also a strong indication of the presence of kauri leafminer.
No predators of this moth have been reported. However, birds and spiders are likely to prey on the moths and caterpillars after they leave the overwintering gall and form their silken cocoon.
New Zealand Forest Service reared parasitoids from kauri leaves with leaf mines in 1954 and 1955. One species of parasitoid wasp (Hymenoptera) has been reared from overwintering galls of the kauri leafminer. Several wasps develop in a gall. The adult wasps chew a hole in the gall through which they escape. There may also be parasitoids that kill caterpillars in leaf mines.
The kauri leafminer, ‘Acrocercops’ leucocyma, forms mines and leaf base (petiole) galls in the young leaves of its only host plant, kauri, Agathis australis (Araucariaceae).
The caterpillars feed on the tissues of the leaf. It first tunnels in the leaf forming a mine just under the epidermis (skin) of the leaf. The mine is initially serpentine, but eventually runs close to the edge of the leaf and extends to the leaf base. Just before reaching the leaf base the mine goes deeper into the mid vein area of the leaf where its feeding induces a gall, a thickening of plant tissue, in which the caterpillar makes a central cavity. The non-feeding (diapausing) caterpillar overwinters in the cavity. In the spring the caterpillar feeds on the internal tissue of the gall.
Wise KAJ 1962. Parectopa leucocyma (Meyrick) (Lepidoptera: Gracillariidae) rediscovered as a leaf-miner of kauri (Agathis australis Salisb.). Transactions of the Royal Society of New Zealand (Zoology) 1(31): 373-375.
Robert Hoare for information about this moth.
The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.
1 August 2018. NA Martin. Photos of mines on fallen dead twig added.
1 August 2017. NA Martin. Photos added of leaves with overwintering galls in middle of leaf.