Chemical composition of horse-chestnut (Aesculus) leaves and their susceptibility to chestnut leaf miner Cameraria ohridella Deschka & Dimic

For over 20 years, trees of Aesculus spp. have been attacked by the larvae of Cameraria ohridella, which causes damage to the leaves. It has been observed that members of the genus Aesculus are characterized by diverse susceptibility to C. ohridella. Four specimens of the Aesculus genus which differ in susceptibility to this leaf miner-Aesculus turbinata (susceptible), Aesculus 9 neglecta (resistant) and two specimens of Aesculus hippocastanum (relatively susceptible and relatively resistant)-were examined. The levels of substances which may function as attractants (chloroplast pigments, anthocyanins), deterrents or repellents (flavonols, phenols), or a source of nutrients (free a-amino acids and carbohydrates) were determined in leaves of these four trees during two growing seasons. The results showed that the more pestsusceptible A. turbinata had, in both growing seasons, significantly higher levels of leaf carbohydrates and anthocyanins than the resistant Ae. 9 neglecta. Thus, anthocyanins and carbohydrates may be the traits which affect oviposition preference and favor the feeding of C. ohridella in the susceptible Ae. turbinata. The relatively susceptible specimen of Ae. hippocastanum contained slightly higher carbohydrate and anthocyanin levels than the relatively resistant one, but only in one growing season. Therefore, it does not explain the causes of their different susceptibility to the pest. The concentration of phenolics in the susceptible Ae. turbinata tree and the relatively susceptible Ae. hippocastanum individual was higher than in the resistant Ae. 9 neglecta and relatively resistant Ae. hippocastanum, respectively. This may suggest that leaf phenolic composition, but not overall concentration, is responsible for different susceptibility of examined trees of Aesculus spp. to the horse-chestnut leaf miner. The present results also demonstrate that the determined chemical compounds do not constitute a complete description of the biochemical relationships between C. ohridella and the examined horse-chestnut trees.