Abstract: 【Aim】 In order to further elucidate the variation of plant volatiles (α-pinene and ethanol) and the aggregation pheromone (2-undecyloxy-1-ethanol) of attractants in lures for Monochamus alternatus in the field and its influence on the trapping efficacy of lures. 【Methods】 The variation in the proportion and composition of the plant volatiles (α-pinene and ethanol) and the aggregation pheromone 2-undecyloxy-1-ethanol of attractants in lures for M. alternatus after being hung in the field for different time were detected by gas chromatography-mass spectrometry (GC-MS). In addition, 20 traps were set up in the forest, and one lure was suspended on each trap. Ten traps were replaced with new lures on the 30th day, and the lures of the other 10 traps were not replaced. The corresponding field trapping efficacy was investigated. 【Results】 The results of variations in the contents of plant volatiles of attractants in lures showed that the initial total content of α-pinene and ethanol accounted for more than 97% in plant volatiles, and there were seven impurities including camphene, pinene oxide, pinocarveol, pinocarvone, myrtenal, verbenone, and myrtenol. The average release rate of plant volatiles was 5.05 mL/d within the first 15 days, and only 0.58 mL/d from the 45th to the 60th day. The results of the composition analysis of plant volatiles showed that the composition and contents of various components in plant volatiles changed with time. The ethanol content was zero on the 15th day, and another three new impurities including verbenol, campholenal and verbenylethylether were present during the 15th-45th day. The contents of the original impurities, i.e., pinocarveol, pinocarvone, myrtenal and verbenone, were significantly increased on the 60th day. The variation in the concentration of the aggregation pheromone 2-undecyloxy-1-ethanol showed that the average release rate of 2-undecyloxy-1-ethanol was 1.05 μL/d within the first 15 days and dropped to 0.52 μL/d from the 30th to the 45th day, and the content of the aggregation pheromone was almost zero on the 45th day. The field trapping test results showed that there was no significant difference in the trapping efficacy between the old lures (hung already for 30 d) and the new lures (newly replaced lures on the 30th day) on the 45th day, but significantly different on the 50th day (P<0.05), and extremely significantly different after the 60th day (P<0.01). 【Conclusion】 The results show that the release rate of attractants for M. alternatus shows the variation tendency of being fast first and then slow in the field, the proportion of each component changes with time, and the main components are oxidized, affecting the trapping efficacy. The high-efficiency duration of the self-made attractants for M. alternatus for field trapping is not less than 45 d, and the validity duration is not less than 60 d. How to better control the release rate of attractants in lures for M. alternatus and delay the component variations is worth further study.

Key words: Monochamus alternatus, plant volatiles, aggregation pheromone, component analysis, validity duration, trapping