Exclusion of ants conditions the efficiency of an attract and reward strategy against Dysaphis plantaginea in apple orchards

Abstract

The rosy apple aphid is a major pest of apple orchards, it is also potentially ant tended. Attract&Reward strategy is a promising pest management method, combining semiochemicals as attractant and companion plants as food sources for natural enemies. However, this method is difficult to implement owing to complex multi-tropic interactions (including mutualist interactions) at play in agroecosystems. Using sentinel plants (apple seedlings bearing rosy apple aphid) we investigated individual and combined effect(s) of Attract&Reward components on aphid biocontrol in early and late spring in apple orchards. The attract component was implemented by adding apple seedlings treated with a plant defense stimulator (inducing plant semiochemicals attractive for natural enemies). The reward component was implemented by adding potted plants producing extrafloral nectar. Moreover, the impact of ant tending on aphids (in exchange of honeydew) was evaluated using exclusion device. We demonstrated that the Attract&Reward strategy enabled increasing aphid biocontrol (vs. control) but only when ants were excluded, and only in early spring. The exclusion device successfully excluded ants in early and late spring but not Araneae and Syrphidae. Araneae and Syrphidae were not affected by the individual Attract&Reward components or their combination. The combination of Attract&Reward components is an effective strategy but only when ants are excluded. This is among the few studies showing experimentally that presence of ants conditions the efficiency of biocontrol strategies, including those based on Attract&Reward concept. A better understanding of trophic and mutualistic interactions is required to design effective conservation biocontrol strategies.