Abstract
Although chemical aspects of plant-insect relationships are largely studied, the effect of within-plant structure on insects is seldom investigated, especially in perennial crops. In fruit production, the manipulation of tree architecture is generally considered to be involved in pest development through considerations of "tree vigour" or branching density. However, both physiological and physical aspects of tree architecture (i.e., canopy height, width and shape, fruiting and vegetative shoot distribution, branching, connectivity, growth rhythmicity) affect the distribution and abundance of both phytophagous arthropods and natural enemies. Tree architecture can affect arthropod pest by modifying: (a) the attractiveness of the host-plant; (b) the within-plant life conditions including microclimate, availability and accessibility of resources and reproduction sites, and enemy-free spaces; (c) the efficiency of chemical or alternative pest control methods (including the use of pheromones). Despite seasonal effects and variability in species biology, modelling and experimental approaches have shown that a more complex architecture favours phytophagous insects and is detrimental to the foraging of most natural enemies. Orchards are permanent habitats, in which the manipulation of tree architecture is potentially a powerful tool for pest regulation, through the implementation of innovating training systems.