Salix alba L. Leaf Volatiles Attract Nematus hequensis Xiao Adults: Sex-Specific Responses and Optimized Field Trapping Using (E)-2-Hexenal and O-Xylene

Plant-derived attractants for sawfly pests are rarely available. This study evaluated field trapping of Nematus hequensis Xiao adults using 15 volatile compounds from Salix alba L. leaves, testing four concentrations, three trap types, two lure cores, two hanging heights, and two trap spacings in a randomized block design (three replicates) during the adult emergence peak in Lhasa, Tibet (2024). Optimal combinations were sex-specific: for females, large boat-shaped traps suspended at 1 m with slow-release bottle lures containing 10 μg/μL o-Xylene captured 62 individuals; for males, the same configuration but with 10 μg/μL (E)-2-Hexenal captured 265 individuals. Trap spacing (10 m vs. 15 m) did not significantly affect daily capture. These results provide a practical, environmentally friendly monitoring tool for N. hequensis. To our knowledge, within the genus Nematus, this study is the first to develop a plant-volatile attractant based on host leaf volatiles.