摘  要  【目的】 21世纪以来，长江三角洲8月下旬-9月上中旬第4代稻纵卷叶螟Cnaphalocrocis medinalis (Guenée)上升成为主害代之一。然而其虫源性质和暴发成灾机制仍不清楚。本研究通过解析2021年南京稻纵卷叶螟后期发生动态和迁飞过程，为该区域稻纵卷叶螟准确测报和科学防控提供理论依据。【方法】基于田间系统赶蛾计数、性诱剂诱捕和雌成虫卵巢解剖数据，结合基于WRF中尺度模式的轨迹分析方法，阐释南京稻纵卷叶螟后期大规模发生的虫源及其大气背景场条件。【结果】 2021年8月下旬-9月上中旬长江三角洲出现的大范围、长时间持续稻纵卷叶螟成虫高峰由两个阶段不同性质的虫源组成。8月24日-9月2日以外地迁入为主，虫源主要来自安徽南部、江西北部、湖南北部以及湖北东部；9月3-14日以本地种群外迁为主，主要降落在安徽南部、江西北部、浙江北部、湖南北部及湖北中部。与常年相比，2021年8月下旬西太平洋副热带高压（简称副高）异常偏强，位置偏南，持续控制在长江以南地区，西南气流贯穿湖南、江西、安徽和江苏等地，经向风风速大于常年；盛行下沉气流期间性诱诱捕的虫量占总虫量的87.29%（419/480），表明副高控制下下沉气流为主是稻纵卷叶螟聚集降落的关键因子。【结论】 特定气候条件下大规模持续迁入是2021年长江下游第4代大规模发生种群的虫源。

Abstract  [Objectives]  To identify the origin of the mass irruption of rice leaf folder (RLF; Cnaphalocrocis medinalis) moths that appeared in late season (late August and early-mid September) rice crops in the Lower Yangtse River Valley (LYRV) in 2021. [Methods]  Monitoring data, including systematic field investigations, sex pheromone trap results, and female ovarian dissection, were used to identify the population characteristics of moths collected during the Nanjing outbreak. A trajectory analytical approach, and the effect of weather on likely migration routes was also analyzed. [Results]  The moths originated from two locations: (i) From 24 August to 2 September most moths were immigrants, and came from southern Anhui, northern Jiangxi, northern Hunan, and eastern Hubei. (ii) During 3-14 September, most moths were local and emigrated towards southern Anhui, northern Jiangxi, and northern Zhejiang. Compared to normal years, the western Pacific subtropical high-pressure system (WPSH) was much stronger, and its orientation was more southerly, covering a large area of Southern China to the Yangtze River. As result, strong southwesterly winds (towards the northeast) prevailed over much of Hunan, Jiangxi, Anhui, and Jiangsu. The wind speed was also stronger than in other years. 87.29% (419/480) of moths were caught by sex pheromone traps when the downward airstream was predominant, suggesting that the downward airstream induced by the WPSH was a key factor forcing RLF moths to concentrate and land. [Conclusion]  Special weather conditions caused high numbers of RLF moths to immigrate into the LYRV in later August 2021. These findings can help develop better integrated pest management strategies for this pest.