The horse chestnut leafminer, Cameraria ohridella, is a micro moth and was discovered for the first time in Macedonia in 1985. Since then, it has quickly spread in Europe. The larva is a leafminer now causing extensive damage in horse chestnut trees (Aesculus spp.) and maple trees (Acer spp.).
The most obvious damage consists of course of the mines caused by larvae. This can evolve to such an extent that mines overlap each other causing a brown discoloration of the leaves which can cause premature leave drop. Attacked trees build up less reserve during summertime and will develop fewer leaves the following year. This weakened condition of attacked trees makes them more susceptible to other pests and diseases.
The moth is 5mm long, with shiny, bright brown forewings with thin, silvery white stripes. The hind wings are dark grey with long fringes. Each female lays about 20-30 eggs on the upper side of a leaf. After hatching, a young larva eats its way into the leaf, and subsequently eats through the leaf tissue, thus forming mines. Cameraria ohridella has five mobile larval stages. The yellowish-green larvae are about 2-5 mm long and have remarkable deep indented segments. When fully grown, the larva pupates in a silken cocoon inside the leaf mine. The horse chestnut leafminer hibernates as a pupa inside the leaves, which have fallen to the ground. The number of generations per year varies from five in South-European countries, to three in Central-Europe and to two in North-Europe, which clearly shows the number of generations is strongly dependent on the climate.