Previous infestation by conspecifics leads to a transient increase of the performance of Sitobion avenae aphids on wheat leaves

1. The ecological niche of aphids is largely defined by the phloem sap of plants, which they consume. Previous studies revealed that aphids may change the phloem sap metabolome and that a previous aphid infestation may benefit them. As aphids reproduce parthenogenetically, the performance and preference of aphids of the same monoclonal aphid lineage can be compared between previously uninfested and previously aphid-infested plants. 2. Wheat (Triticum aestivum) leaves were infested by clonal lineages of Sitobion avenae aphids for 9-10 days. Leaf phloem exudates were analysed using amino acid profiling and metabolic fingerprinting, capturing mainly specialised metabolites. It was investigated whether aphid colony sizes differ between leaves that were previously uninfested or infested by aphids of a different clonal lineage or by aphids of the same clonal lineage and whether aphids show a preference for any of these leaves. 3. The relative concentrations of metabolites in the phloem exudates were not affected by aphid infestation. Aphid colonies were partly larger on previously aphid-infested leaves than on control leaves. However, this effect was transient and finally colonies had similar sizes. Given a choice between previously aphid-infested and uninfested leaves, S. avenae nymphs showed no preferences. 4. The findings that positive effects of previous aphid infestation on aphid performance are transient and that the performance but not the preference of the aphids was affected by previous aphid infestation highlight the temporal dynamics and complexity of aphid-plant interactions. Niche alteration processes may be partly involved in these interactions.