Prior Cereal Leaf Beetle (Oulema spp.) Window-Pane Feeding Has Weak Systemic Legacy on the Wheat Dwarf Virus Vector Psammotettix alienus in Barley

Plant-mediated interactions can modify herbivore behaviour and vector-borne plant disease dynamics, yet the systemic consequences of prior cereal leaf beetle (Oulema spp.) window-pane feeding for later phloem feeder vectors remain unclear. We hypothesised that prior Oulema window-pane feeding induces systemic changes in barley that alter the subsequent host acceptance and feeding behaviour of Psammotettix alienus. Plants received one of three 24 h treatments on one leaf: Oulema pre-colonisation, standardised artificial vascular injury or an undamaged control. Leafhopper responses were measured on a different, systemic leaf using female choice assays and electrical penetration graph recordings. Oulema damage was low and strongly right-skewed and did not affect most feeding variables, including non-phloem activities, phloem activity, drinking latency or phloem activity latency. Artificial vascular injury, however, reduced the phloem–saliva ratio in females, which indicates a lower relative investment in phloem preparation once the phloem phase was reached. Within Oulema-treated plants, increasing damage reduced the number of transitions between penetration phases in males but not females. Females showed no treatment-related preference in salivary sheath production or oviposition. Thus, Oulema window-pane feeding left only a weak systemic plant-mediated legacy for P. alienus, closer to behavioural neutrality than strong facilitation or interference under these short-term systemic experimental conditions.