Horse chestnut leaf miner (Cameraria ohridella) is an exotic insect pest which lives in horse chestnut trees. It was first reported in the UK in 2002, in Wimbledon, and has since spread north, south and west across most of England.
Its larvae (caterpillars) mine within the leaves, and large numbers, can destroy most of the leaf tissues. Although it can cause severe damage to horse chestnut leaves and discolouration and defoliation before normal autumn leaf-fall, on its own this pest does not significantly damage tree health, however there are fears that climate change and possible interactions with other pests and diseases may lead to this being a more significant threat in the future.
Horse chestnut leaf miner moths fly out from an infested site or are carried, along with infested leaves, on vehicles, infesting new areas, sometimes many miles from the original site.
Damage may be reduced by removing fallen leaves during the autumn and winter and either composting them thoroughly, to destroy the over-wintering pupae, or by covering small heaps of leaves with a layer of soil or other plant material to stop the adult moths emerging in the spring.
For more information visit http://www.forestry.gov.uk/horsechestnutleafminer.