The leaf miner Cameraria ohridella causes premature defoliation in Aesculus hippocastanum. The impact of the parasite on seasonal changes of water relations, hydraulics and growth of three-year-old A. hippocastanum seedlings was investigated. Leaf expansion was complete before the adults of the moth developed, so that growth of infested seedlings was similar to that of controls. Leaf conductance to water vapour of infested seedlings was reduced with respect to controls, both in mined and in still green portions of attacked leaves. In July and August, the hydraulic resistance of infested seedlings was higher than that of controls, due to anticipated increase of hydraulic resistance at the leaf, petiole and current-year stem level. This was interpreted as evidence of anticipated leaf senescence in infested plants, leading to early leaf abscission. Nevertheless, our data suggest that, under our experimental conditions, C. ohridella is not a major mortality factor for A. hippocastanum seedlings.
