Experience from Europe indicates that once established, this moth will cause severe damage to the foliage of horse chestnut on an annual basis, and defoliation before normal leaf-fall in the autumn. The larvae mine within the leaves and at high population densities they can destroy most of the leaf tissues.
The horse chestnut leaf miner (Cameraria ohridella) was first observed in Macedonia, in northern Greece, in 1985 and was described as a new species in 1986. In 1989, it appeared unexpectedly in Austria and since then it has spread throughout central and eastern Europe. It was first found in Great Britain in 2002 in the London Borough of Wimbledon. Over the years its range has expanded, and it can now be found at many locations in south-east England.
How is it spread?
Dispersal of the moth from infested areas occurs on a broad front through adult flight, assisted by the wind, and through the passive transport of adult moths or infested leaves in or on cars and other vehicles. Transportation by vehicles appears to be responsible for the sudden appearance of the moth in towns and cities a long way from known areas of infestation.
Damage can be reduced by removing fallen leaves during the autumn and winter and either composting them thoroughly, to destroy the over-wintering pupae, or if the leaves are collected into smaller heaps, by covering them with a layer of soil or other plant material to prevent adult emergence in the following spring.
There is no requirement to report sightings of this pest to us but you can help monitor its spread and contribute to other research into horse chestnut leaf miner - www.ourweboflife.org.uk