Resistance of apple cultivars to Dysaphis plantaginea (Hemiptera : Aphididae): Role of tree phenology in infestation avoidance

To test the importance of ßowering phenology in damage caused to apple cultivars by rosy apple aphid, Dysaphis plantaginea (Passerini) (Hemiptera: Aphididae), susceptibility of 16 cultivars was compared in greenhouse conditions after infestation with aptera and in the Þeld after natural tree colonization. Flowering phenology was recorded in the Þeld for all the cultivars. In both greenhouse and Þeld trials, there were differences among cultivars with respect to aphid infestation and damage. However, damage in the greenhouse and Þeld was not signiÞcantly correlated. Flowering phenology was also different among cultivars. Flowering order among cultivars was signiÞcantly negatively correlated with aphid infestation and damage in Þeld, i.e., early leaÞng cultivars showed higher infestation and damage than late-leaÞng cultivars. If egg hatching occurs before bud bursting, neonate larvae will suffer a high mortality because they cannot feed on these late cultivars. A later recolonization of these trees is hampered because (1) winged aphids cannot live on apple but only on the secondary host, (2) apterous forms have a limited dispersal capability, and (3) aphid predators progressively increase in the orchard. Therefore, synchronization between egg hatching and bud bursting is of critical importance in the success or failure of infestation