Olfactory responses of Philaenus spumarius nymphs to plants from field margins of Mediterranean perennial crops

Field margins are important semi-natural habitats in agroecosystems, but may also host insect vectors such as Philaenus spumarius , the main European vector of Xylella fastidiosa . Despite its epidemiological relevance, nymphal behaviour in detecting and selecting host plants is poorly understood. This study aimed to evaluate the locomotor capacity and olfactory responses of P. spumarius nymphs to plant species commonly found in field margins of Mediterranean perennial crops ( Cistus ladanifer , Foeniculum vulgare , Lavandula stoechas , Rosmarinus officinalis and Thymus mastichina ), as well as to explore potential relationships between behavioural responses and the profiles of plant volatile organic compounds (VOCs). Nymphs from different instars were assessed in locomotion assays without food stimuli and in olfactory tests using a Y-tube olfactometer, while plant volatile profiles were characterised by HS/SPME GC-MS. The results showed that nymphs from the N2–N3 and N4–N5 instars exhibited similar locomotor capacities, with no significant differences in total distance moved or mean velocity. Olfactory responses differed significantly among plants, with C. ladanifer showing a lower probability of being selected compared to the other species, indicating a potential avoidance or reduced attractiveness effect. Decision latency varied significantly depending on both nymphal instar and plant species. A total of 104 VOCs were putatively identified, and exploratory plant-level analyses identified carvone as a candidate compound associated with short-term olfactory choice patterns. However, this association requires validation. These findings suggest that plant-emitted chemical cues were associated with differential olfactory responses of P. spumarius nymphs under controlled Y-tube conditions, contributing to a better understanding of plant–insect interactions and providing information for the development of sustainable integrated pest management strategies.