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Mahoe leaf miner - Liriomyza flavolateralis

By N A Martin (2010)

Classification
Class:Insecta
Order:Diptera
Family:Agromyzidae
Scientific Name:Liriomyza flavolateralis (Watt, 1923)
Mahoe leaf miner: Liriomyza flavolateralis (Diptera: Agromyzidae), the flies are about 2.5-3.2 mm long, (photograph by Tim Holmes, copyright Plant & Food Research).
Mahoe leaf miner: Liriomyza flavolateralis (Diptera: Agromyzidae), the flies are about 2.5-3.2 mm long, (photograph by Tim Holmes, copyright Plant & Food Research).
Two mines of the mahoe leaf miner: Liriomyza flavolateralis (Diptera: Agromyzidae), in a leaf of mahoe, Melicytus ramiflorus, (photograph by Nicholas Martin, copyright Plant & Food Research).
Two mines of the mahoe leaf miner: Liriomyza flavolateralis (Diptera: Agromyzidae), in a leaf of mahoe, Melicytus ramiflorus, (photograph by Nicholas Martin, copyright Plant & Food Research).
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Synonyms


Agromyza flavolateralis Watt, 1923

Phytobia flavolateralis (Watt, 1923)
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Biostatus and Distribution

This endemic fly is found throughout New Zealand where its host plant, mahoe, Melicytus ramiflorus, is found. It appears to be restricted to native ecosystems. It is present in native reserves in cities, but does not appear to spread to new restoration areas unless the host plant is present in a remnant of the original forest.

Conservation status: Widespread, not threatened.

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Life Stages and Annual Cycle

The fly breeds all year. There is a winter generation and several generations in the spring and summer.

Adult fly

The flies are small, about 2.5-3.2 mm long, similar to the size of vinegar flies, Drosophila, that are seen around rotting fruit. The body is grey with yellow areas on the sides of the thorax( the middle part of the body to which the legs and wings are attached). They also have short yellow antennae. It is a typical fly, having one pair of wings. The hind pair of wings is reduced to two small knobs, or halteres, which help the fly to balance during flight. The male has rounded black external genitalia at the end of the abdomen, while the female has a slender end containing an ovipositor. The ovipositor is used to make holes in young leaves into which eggs are laid. Females of other species of this kind of leaf-mining fly also make holes with their ovipositor and feed on the leaf sap. This has not been observed for this species.

Eggs and larvae

Single eggs are inserted into young leaves, usually near the midrib. The newly hatched larvae tunnel into the leaf making a mine that is visible on the upper side of the leaf. The larvae feed on the internal cells of the leaf. They have a single black jaw which is moved from side-to-side, scraping the plant cells at the head of the mine. The plant cells are ingested and the dark green faeces excreted into the mine behind it, generally to the sides of the mine. The larva moults, or changes skin, as it gets larger. There are three larval stages (instars). A fully grown larva is about 3 mm long.

The mine starts near the midrib of the leaf and meanders over the leaf. The mine is narrow at first, gradually widening.

Pupa

When fully grown, the larva makes a semicircular slit in the thin upper wall of the mine. The larva usually drops to the ground into the soil or litter. The larva pupates inside its larval skin, which turns brown and hard. This structure is called a puparium. The puparium has a pair of stigma (organs for breathing) at each end of the body. After several weeks, the eyes and bristles of the adult fly can be seen through the skin of the puparium.

Fly emergence

When ready to emerge, part of the head, just above the antennae, balloons out. This structure, the ptilinum, pushes the front of the pupa open. There is a line of weakness between the top and bottom halves of the first three and a half segments that splits allowing the top and bottom to open up. After the fly has crawled out, the ptilinum retracts into the head. The fly wings expand and the body hardens. Over the next 12 hours the fly acquires its full body colour.

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Recognition

Leaf mines of the mahoe leaf miner: Liriomyza flavolateralis (Diptera: Agromyzidae), in a leaf of mahoe, Melicytus ramiflorus, normally there are only one or two mines in a leaf. (Photograph by Nicholas Martin, copyright Plant & Food Research).
Leaf mines of the mahoe leaf miner: Liriomyza flavolateralis (Diptera: Agromyzidae), in a leaf of mahoe, Melicytus ramiflorus, normally there are only one or two mines in a leaf. (Photograph by Nicholas Martin, copyright Plant & Food Research).

These small grey and yellow flies require expert knowledge for identification. However, the species can be detected by the leaf mines.

These are the only leaf mines known on mahoe, Melicytus ramiflorus. Leaf mines have been found in other species of Melicytus, but these are believed to be caused by other, closely related species of fly.

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Natural Enemies

Predators

There are no reports of predators of the flies, but it is likely that they are preyed upon by birds, spiders and predatory insects.

Parasitoids

The only species of parasitoid that has been reared from the mahoe leaf miner: Liriomyza flavolateralis, is a species of Chrysonotomyia (Hymenoptera: Eulophidae).

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Host Plants

Leaf mine of the mahoe leaf miner: Liriomyza flavolateralis (Diptera: Agromyzidae), in a leaf of mahoe, Melicytus ramiflorus, (photograph by Tim Holmes, copyright Plant & Food Research).
Leaf mine of the mahoe leaf miner: Liriomyza flavolateralis (Diptera: Agromyzidae), in a leaf of mahoe, Melicytus ramiflorus, (photograph by Tim Holmes, copyright Plant & Food Research).

The fly lives only on Melicytus ramiflorus J. R. et G. Forst. (Violaceae) (mahoe, whiteywood). The adult female fly makes small punctures in young leaves for egg-laying and possibly for feeding. The larva burrows through the leaf making mines that are visible from the upper side of the leaf. The mine starts near the midrib, gradually getting wider and making a serpentine pattern.

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Additional Information

The mahoe leaf miner appears to be restricted to native ecosystems or areas where mahoe has persisted after much of the other original vegetation has been removed. It may be a good indicator of the history of an area. It is not known how readily it will colonise newly restored areas of native vegetation that are not connected to remnants of the original native forest.

It should be easy to survey populations of the fly, though populations tend to be low and mines tend to be found on particular trees that probably had leaves of a suitable age for feeding by the adult female fly and for egg laying.

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Information Sources

Spencer KA 1976. The Agromyzidae of New Zealand (Insecta: Diptera). Journal of the Royal Society of New Zealand 6(2): 153-211.

Watt MN 1923. The leaf-mining insects of New Zealand: part III - species belonging to the genus Agromyza (Fallen) and Phytomyza (Fallen). Transactions and Proceedings of the New Zealand Institute 54: 465-489.

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Acknowledgements

The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.

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