The effect of rosy apple aphid and beneficial insect dynamics in an orchard
Abstract: The natural control of the rosy apple aphid Dysaphis plantaginea, a major pest in European apple orchards, was studied from 2006 to 2008 in three organic apple orchards planted with Smoothee 2832T®, Ariane and Melrose cultivars. The development of D. plantaginea and the beneficial complex associated with aphid colonies were visually assessed in the spring, and the effect of the interaction within the orchard (edge, inner and intermediate areas) was studied. Infestation of orchard edge trees by D. plantaginea was higher. Beneficial numbers and the predator/prey ratio were also higher in edge trees in 2007, and 2008. Predatory arthropods that were assessed within infested shoots mainly comprised Syrphidae, Cecidomyiidae, ladybirds and earwigs, but their proportion differed between cultivars. It also differed between areas of the orchard: Cecidomyiidae were assessed earlier and also prevailed in edge areas, whereas Syrphidae prevailed in the inner parts of the orchards. However, even the most favourable situations did not permit the natural control of D. plantaginea. These results suggest that the cultivar affects both D. plantaginea and associated predatory arthropods, and that the management of edge effects through orchard redesign and/or cultural practices deserves to be considered for the management of the rosy apple aphid in IPM orchards.