Ecological consequences of occurrence of the horse chestnut leaf miner (Cameraria ohridella) and leaf blotch on the horse chestnut (Aesculus hippocastanum)
The horse chestnut (Aesculus hippocastanum L.) is species widely distributed in Europe. It is often an element of urban and rural landscape. From the end of 80’ of XX c. very fast dispersion of horse chestnut leaf miner (Cameraria ohridella Deschka&Dimić, Lepidoptera: Gracillariidae) was observed in Europe. In the moderate climate conditions it develops at least three full generations per year causing premature leaf fall. In effect, physiological disorder is observed and one evidence is often observed secondary flowering of the horse chestnut trees in late summer. Second important factor causing damage of assimilative apparatus of the horse chestnuts is leaf blotch disease, caused by fungal agent (Phyllosticta paviae Desm., Ascomycota: Phyllostictaceae; syn.: Guignardia aesculi (Peck) V.B. Stewart).
Conducted investigations on ecological and physiological aspects of occurrence of both organisms on the horse chestnut was aimed for explanation of competition for the same resources phenomenon as well as potential and universality of host-plant defence reactions. The general goal of the research may be pointed as follows: recognising the physiological reaction of host-plant on assimilative apparatus damage (1), identifying aspects of insect ontogenesis under different environmental conditions (2), and measuring the dynamics of fungal infection development on plants occupied or not occupied by C. ohridella (3).
Results included in the articles consisted in this thesis indicates that from the ecological point of view, co-occurrence of both parasites on one host plant makes unfavourable conditions for each of the species in this tripartite interaction. A greater content of a condensed tannins in leaves of the horse chestnut, as a results of abovementioned phenomenon, is more unfavourable for the development of fungal infection. Plants investment into this metabolites is only reducing the damage dynamic. Apart from this, available resources allocated into synthesis of defence metabolites decreased A. hippocastanum growth.
Thesis also presents the results of a research conducted in the topic of influence of light conditions on changes in the anatomy and chemical composition of the A. hippocastanum leaves and following consequences for insects ontogenesis. Performance parameters such as pupae mass and food utilisation efficiency was better when the larvae fed in leaflets of plant under low light conditions. However, it was indicated that in a leaf blade tissues of the A. hippocastanum used by the C. ohridella larvae during growth, alimentary deterrents may be missing. Moreover, the potential fecundity of C. ohridella, expressed by number of oocytes in ovaries of females in imaginal stage was on average the same independently from the type of food consumed during their ontogenesis.
Interaction between P. paviae and C. ohridella as result of colonisation of the same space for development is more unfavourable for the latterly mentioned species. That because of limited ability of the leaf miner larvae relocation. Females of the C. ohridella are spreading the risk for potential larvae starving by ovipositing on many leaflets. Moreover, females deposited eggs mainly in places recognised organoleptically (by the human) as healthy. Necrosis being the effect of infection by the P. paviae, was not factor explaining the observed eggs frequencies on A. hippocastanum leaflets. The strength of antagonistic impact of P. paviae on C. ohridella having a nature of the competition was to some extent reduced on the favour of insect.