Larvae of C. ohridella mine within the leaves of horse chestnut, and the damage caused by large numbers of larvae can be striking. Up to 700 leaf mines have been recorded on a single leaf under favourable conditions. Severely damaged leaves shrivel and turn brown by late summer and fall early, well before normal leaf fall in the autumn.
Leaf mines of Cameraria ohridella on horse chestnut,
Wimbledon, London, July 2003
Defoliation by Cameraria ohridella,
Wimbledon, September 2003
The spread and establishment of C. ohridella is of particular concern because once established, the moth appears always to maintain exceptionally high rates of infestation without any evidence of decline. In European towns and cities there has been no decrease in populations even after many years, and severe damage to horse chestnuts has occurred on an annual basis, greatly impairing the visual appearance of the trees.
It takes 2-3 years after C. ohridella first establishes in a new area for populations to build up to densities high enough to cause severe damage and defoliation. Up to 2006, severe damage was restricted to London and the Home Counties, parts of East Anglia and some locations in the Midlands. Over the last two years, severe damage has been reported from much further afield, particularly south Wales and many parts of southern England.
Damage caused by C. ohridella in 2006