INDIRECT TWO-WAY INTERACTIONS BETWEEN APHIDS AND A PATHOGEN ON ROSES

Indirect interactions between plant pathogens and phytophagous pests can occur when infestation by an attacker alters the shared host in a way that affects another attacker that could be spatially or temporally separated from the first one. The most commonly invoked scenario involves the induction of plant defence reactions which primarily depend on characteristics of both pathogens and herbivores considered. We carried out experiments under controlled conditions on young rose plants in order to assess the impact of such indirect interactions on life history traits of two pests on rose: a necrotrophic fungus, Botrytis cinerea, and an aphid, Rhodobium porosum. We highlighted (1) an indirect two-way negative interaction between B. cinerea and R. porosum which is expressed by a reduction of aphid growth rate and a decrease in growth speed of fungal lesions on the plants, and (2) a negative indirect effect of B. cinerea on insect’s behaviour, as aphid preferred B. cinerea-free plants than B. cinerea-infested plants when given a choice. The implications of results in Integrated Pest Management on rose and mechanisms involved in the interactions are both discussed.