Exclusion of third-party arthropods conditions the efficiency of an attract and reward strategy against Dysaphis plantaginea in apple orchards

The rosy apple aphid is a major pest of apple orchards, potentially ant tended. The use of generalist insecticides is the principal management method to control this pest. Lately, the attract and reward strategy has emerged as a promising conservation biological control method, combining semiochemicals as attractant, and companion plants as natural enemies’ supplementary food sources. Because of complex trophic and mutualistic interactions within the agroecosystem between the pest and other arthropod species, this strategy has to be carefully evaluated. We conducted a sentinel plant experiment in apple orchards to investigate the individual and combined efficiency of the attract and reward strategies to control rosy apple aphid in early and late spring. The proximate environment of each potted apple sentinel plants was manipulated by the addition of potted semiochemicals-emitting apple seedlings and/or a potted extrafloral nectar producing plant. An exclosure factor was added to evaluate the role of ground dwelling predators and ants. We observed that the attract and reward strategy significantly increased the biological control of the rosy apple aphid only when third party arthropod were excluded and in early spring. Exclusion did exclude ants in early and late spring; we did not find any effect of the exclusion nor of the individual or combined attract and reward strategies on Araneae and Syrphidae. Attract and reward components combined appears to be an effective strategy, if third party arthropods are excluded. This study emphasizes that understanding trophic, competitive and mutualistic interactions is needed to design effective conservation biological control strategy.