IntroductionLeaf miners are a large, highly specialized trophic group treated as parasites whose larvae feed inside the plant tissue. Often they are classified by the shape of the mine that they create. Many leaf-mining species are an important and conspicuous element of insect fauna, and plenty of them are known as pests of fruit trees and shrubs (Buszko, 1990). Of significant interest of this group are the Phyllonorycter species, the dominant genus of the family Gracillariidae (Lepidoptera). Mostly woody plants have been reported as their hosts, with the Fagaceae, Betulaceae, and Salicaceae especially favored (Beiger, 2004).In Poland, 22 species of leaf miners are known to feed on hazel leaves. Two of them are from the genus Phyllonorycter, namely Ph. coryli (Nicelli 1851) and Ph. nicellii (Stainton 1851) (Beiger, 2004). They feed on the leaves of the common hazel (Corylus avellana L.) as well as on the purple-leaved hazel (Corylus maxima Mill. cv. 'Purpurea'), which is frequently planted as an ornamental in gardens and urban environments (Dimič, 1971;Gantner et al., 2005;Górska-Drabik and Gantner, 2005, 2006). Ph. coryli is an upper-side miner (Askew and Shaw, 1974) and its mine begins as a small silvery spot; then the chamber increases and the skin folds. In turn, Ph. nicellii is an under-side miner and the mine is not too large, heavily bulging with a marbled pattern (Beiger, 2004).Phyllonorycter leaf-miners are great subjects for examining the interaction between phytophagous and parasitoids (