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Horse-chestnut Leaf Miner

  category:Frequently Asked Questions

Introduction

The Horse-chestnut Leaf Miner (Cameraria ohridella) is a tiny species of moth (Family Gracillariidae) which lays its eggs in the leaves of horse-chestnut (Aesculus hippocastanum) trees. Because horse-chestnut is not a native tree, it has very few parasites, hence the ravages caused by the leaf miner are both almost unique and very easy to spot.


The only other damage likely to be confused is by a fungus (Guignardia aesculi), but damage caused G. aesculi produces large red-brown blotches that tend to be concentrated at the tips and margins of the leaflets, superficially resembling leaf mines. Unlike C. ohridella mines, the blotches caused by the fungus are often outlined by a conspicuous yellow band and do not appear translucent when held up to the light. Later, Guignardia infections produce tiny black pimples (pycnidia) on the browned parts, mostly on the upper surface. Leaflets severely affected by Guignardia roll upwards longitudinally and, like leaves infested by C.ohridella, may fall prematurely. Unlike C.ohridella, the damage, although unsightly, occurs after most of the growth of the tree has taken place. Guignardia leaf blotch is widespread and common in the southern half of England, becoming less frequent northwards[1].
Hclm.jpg
The adult moth © Craig Slawson, 2014

History

Hc leaf.jpg
Infected horse-chestnut leaf © SER, 2013
Cameraria ohridella was first reported in Macedonia in 1985 and has spread rapidly across Europe. It was first seen in the UK in London in 2002 and the first Staffordshire sightings were in the Walsall area in late 2007. It has since spread across most of Staffordshire.


The mines produced by Cameraria are very distinctive, often clearly restricted to the area between veins in the leaf. The moth itself, although very pretty is only 4mm long (wingspan 8mm) so easily overlooked, therefore the best method of monitoring this species has been to record the occurrence of the mined trees.

References

  1. Forestry Commission Exotic Pest Alert - Horse chestnut leaf miner

Created by SER © 2018 The Wolseley Centre, Wolseley Bridge, Stafford. ST17 0WT Last updated 19/05/2015 
Operated by: Staffordshire Wildlife Trust, Staffordshire County Council and Stoke-on-Trent City Council