The expected high efficacy of Dimilin but also good protection by treatment with Confidor and Calypso were demonstrated. Mospilan was less effective. A high mortality of ultimate larval instars of the leafminer and their substantial parasitisation was observed in experiments with potted seedlings on Confidor and Calypso treated leaves of horse chestnut, Aesculus hippocastanum. The parasitoids found in mines with larvae and pupae of C. ohridella on A. × carnea and A. hippocastanum were recorded and determined. The most abundant species was Minotetrastichus frontalis (Chalcidoidea, Eulophidae). The possible effect of insecticide treatments on parasitisation of the horse chestnut leafminer is discussed.