Phyllonorycter leucographella

The Firethorn Leaf-miner

Phyllonorycter leucographella is a small gracillariid moth, the larvae of which mine the leaves of Pyracantha. The moth was accidentally introduced into the UK sometime in the mid 1980s, and from 1990 to 1993 I studied the spread of the species in England while working at Imperial College at Silwood Park.


Life Cycle

The eggs of P. leucographella are laid on the midrib of leaves of Pyracantha - They are pale green, about 0.2 mm long, and only just visible to the naked eye.

When densities of the moth are high, several eggs may be laid on each leaf, but it is rare for more than one moth to merege - The young larvae fight with each other until there is only one survivor.

The first instar larva (see right - scale bar is 1 mm) emerges through the base of the egg after a few days and starts to tunnel along the midrib of the leaf, under the leaf's surface.

The larva has a very flattened head with scissor-like jaws which are used to slice through the cells of the leaf, feeding as it goes - The caterpillar in effect swims through the leaf.

The second and third instar larvae retain the flattened body shape of the first instar and enlarge the mine sideways away from the midrib until it becomes a blister. At this stage the mine is quite obvious, and many caterpillars are killed by birds.

The fourth instar larva (right) is more conventionally caterpillar-shaped, and spins silk across the leaf-mine.

As the silk contracts it pulls the leaf together into a sort of pod (left). This may serve to make the mine less conspicuous, as well as giving the later larvae more room to feed...

The fourth and fifth instar (right) larvae feed by biting down into the leaf tissue on either side, leaving characteristic depressions.

When ready to pupate, the fifth instar caterpillar cleans out one end of the mine, removing all frass (droppings) and debris.

It then walls itself into that end by spinning a disc of silk across the mine. Here it pupates, presumably isolated from any pathogens that can develop on its old droppings and the leaf tissue.

When the pupa is ready to emerge as an adult, it punctures the mine with a pointed projection on its head, and wriggles half out of the mine, still leaving it's rear end attached with silk.

The adult then emerges, leaving the empty pupal case sticking out of the now-deserted leaf-mine (left)


Spread of the Firethorn Leaf-miner in the UK

The picture to the right is an animated GIF that shows the spread of the Firethorn leaf-miner in the UK from 1990 to 1993, as recorded by the Firethorn Leaf-Miner Project at Silwood Park.

Red dots represent 10km national grid squares in which the moth was at high density in any year. Yellow dots represent grid squares in which the moth was at low density.

For this survey, low density mean that although the moth was found in the grid square, no Pyracantha bush had more than 1% of its leaves with mines. High density means that more than 1% of leaves were mined on at least some bushes. Up to 90% of leaves were mined on some bushes in southern Essex.

The pattern of spread shows a steady advance of the moth by about 20km per year, but with a few isolated colonisations occurring outside the main area of spread. These seem to have been through the movement of infested Pyracantha bushes by the garden-centre trade.

See the following reference for more details:

Nash, D.R., Agassiz, D.J.L., Godfray, H.C.J. and Lawton, J.H. (1995) The pattern of spread of invading species: two leaf-mining moths colonizing Great Britain. Journal of Animal Ecology 64, 225-233.

How far has the firethorn leaf-miner spread now? This is a questiuon that I hope to answer with your help. I hope to soon have a web page where records of the moth can be submitted. In the meantime, you can always contact me with records.


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