The response of pear cultivars and wild species of Pyrus to Psylla sp. attack, depending on genotype, based on eggs' and nymphs' presence on the leaves, before and after the treatment with insecticide

Psylla species are one of the most dangerous pests for pear cultivars. In order to evaluate the response of different pear genotypes to psylla attack and the efficiency of Novaluron insecticide, 177 pear cultivars and 15 wild species of Pyrus were analysed in natural conditions of strong infestation, in the absence of other treatments. The conditions were the same for all genotypes (age of trees, rootstock, orchard management, etc.). The observations were made before the treatment with Novaluron, in the first week of June, and after one month of the treatment, in the first week of July, based on eggs and nymphs presence on the leaves. The number of psylla eggs deposited on the leaves before the treatment oscillated within very large limits, between 0.0 and 299.7 eggs leaf-1 (for 177 cultivars) and 2.0-168.7 eggs leaf-1 (15 wild species). After treatment, a much smaller number of eggs with a viable appearance on the leaves were found compared to `before treatment' (from 81.1 to 8.1 eggs leaf-1 as the mean of 177 cultivars and from 55.1 to 12.6 eggs leaf-1 as the mean of 15 wild species), demonstrating a good effectiveness of the insecticide. For nymphs' presence, the difference as the mean for all cultivars and species between before and after treatment was insignificant. The extreme amplitude of variation between the analysed genotypes expresses the preference of the pests for a certain "host", on which to lay eggs, and the level to which harmful insects can infest the plants. The differences between genotypes reflect the existence of genetic resources in pear germplasm and the study has ensured identification of some genotypes which can be used in pear breeding, in order to improve the resistance of pear to Psylla sp. attack.