Résumé
Plant architecture governs living conditions of herbivores. In fruit trees, the perennial structure is modulated by training and pruning which may affect pests. The effect of tree architecture manipulation on the development of the rosy apple aphid Dysaphis plantaginea (RAA) was investigated from 2002 to 2009 in apple orchards. The first step (2002-2005) consisted in comparing the Centrifugal Training system (CT) with extinction pruning (i.e., selective removal of spurs at bud-burst to favour light penetration and spur fruiting) to the Solaxe system (OS) with no extinction pruning. RAA infestation was significantly lower in CT trees 2 years out of 4. The hypothesis of a within-tree structural effect on RAA development was proposed beside possible microclimatic and mechanical (i.e., infested shoot removal) effects. In a second step (2007-2008) we investigated the relationships between the branch structure and RAA development in both training systems. In CT trees, branches displayed higher shoot orders compared to OS. Infestation dynamics presented similar patterns in both systems, but RAA spreading rate was lower in CT trees. These results suggested that the complexity of the aerial system due to higher branching orders affected insect movement within its habitat. In 2009 a glasshouse experiment with oneyear- old potted apple trees was carried out to test the combined effect of simplified architectures (1 vs. 2 extension shoots per tree) and of three nitrogen regimes on the development of RAA artificially set on the trees. There was no significant difference in aphid numbers at peak infestation between architectural treatments although RAA migration was earlier with 1 extension shoot. Moreover, a higher aphid population was shown for intermediate nitrogen regimes highlighting the pest response to trophic parameters. These experiments confirm the importance of tree training strategies in the management of orchard pests. They provide avenues to design sustainable orchard systems based on cultural methods giving partial control of pests.