“…This may produce physiological changes in the plant that reduce its quality as a resource. For example, phloem composition may be negatively affected (Olmstead et al, 1997;Petersen & Sandström, 2001), defences selectively deleterious for one of the competitors triggered (Moran & Whitham, 1990;Inbar et al, 1999;Messina et al, 2002), phloem flow among plant tissues modified (Inbar et al, 1995), or plant volatile composition changed (Bernasconi et al, 1998). In our system, some changes associated with aphid infestation are conspicuous (for instance, the presence of leaves with chlorotic spots, honeydew, and moulds), but the specific plant changes responsible for the competition observed are unknown.…”