The plant defence syndromes (PDSs) concept predicts host plants should develop diverse resistance profiles against their herbivores. We used Electrical Penetration Graphs (EPG) to investigate complex and genotype-specific penetration-barriers to Chaitophorous tremulae aphid feeding on Aspen (Populus tremula). Leaf condensed tannins were associated with enhanced probing activity and increased ingestion of xylem sap. Aphids probed less on Aspen genotypes low in tannins, suggesting other defence traits might be elicited. Our results support the idea of multi-layered PDS defence traits, and provide evidence of high plasticity in tannin profiles across temporal and spatial scales. We conclude that tannin plasticity may form a dynamically unpredictable aspect of the PDS defence arsenal that protects Aspen against piercing-sucking aphids.