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Leopard moth (Zeuzera pyrina)
This stem-boring pest attacks a wide range of deciduous trees and shrubs.
Hosts
Leopard moth caterpillars tunnel in branches and trunks with a diameter of up to 10cm (4in), making them prone to breaking. Fruit trees (especially apple and pear) and Sorbus species are favourite host plants; others include birch, Amelanchier, lilac, Cotoneaster and oak.
Symptoms
Branches or the trunks of sapling trees break in windy weather, revealing a tunnel through the centre or under the bark. Excrement pellets of compacted sawdust may accumulate around or underneath the entry hole made by the caterpillar - which is creamy white with many black spots and a brown head. It is up to 50mm long when fully grown.
Biology
The adult moth lays eggs singly on small shoots in midsummer. The young caterpillars cause little noticeable damage but in their second year will bore into larger branches and trunks. They usually complete their feeding and pupate in their tunnels during late spring of the third year. There is often only one caterpillar in an affected tree.
Control
Prune a damaged branch back to sound wood to remove the caterpillar. Otherwise insert a piece of wire into the tunnel to skewer the caterpillar. There is no effective preventative measure that can be taken against the adult moth.