Cameraria ohridella was first confirmed in Ireland in south Dublin during 2013. In recent weeks, (June & July 2014) as well as throughout Dublin, mines and adults have been noticed in Belfast, Cavan, Louth and Wicklow and while many searches of trees have been negative it is likely to be more widespread than the current distribution map indicates.
As I write this the 2 maps above are the same. The map on left will stay fixed as a snapshot of what is known on 1st Aug 2014, the right map will update when further sightings are confirmed.
We would like you to look for mines of this species in your area on Horse Chestnut trees (Conker Tree) While fresh mines are distinctive, the old mines are brown as is leaf blotch, a fungal disease which can be found, sometimes very extensively on practically all Horse Chestnut trees. For the inexperienced this blotch can be easily interpreted as mines. If in doubt it is probably blotch
If you feel you have a definite sighting of a mine, forward a photo via Ask an Expert
If we can confirm we will add your sighting to the map.
The following 3 photos, courtesy of Dave Allen indicate of what to look out for. the fresh mines are pale and obvious. Part of the mine is usually a darker blotch and frass and a caterpillar may be visible. The mines may join together and many caterpillars may be visible together. The most likely location on tree is low, usually within reach and often near the trunk. The caterpillar pupates inside the mine. The 2nd photo shows an exit case. These are often seen sticking out of the leaf. If it has fallen out then a hole is left. The 3rd photo shows many mines in a leaf.
Cameraria ohridella has a very recent history having been first observed in Macedonia in 1984. It was first observed in Britain in 2002
See wikipedia for more info