Migration Dynamics of Fall Armyworm Spodoptera frugiperda (Smith) in the Yangtze River Delta

SIMPLE SUMMARY: Fall Armyworm Spodoptera frugiperda (Smith) is one of the most important agricultural pests, which seriously threatens agricultural production and food security in China. The Yangtze River Delta is an important passage for the northward migration of S. frugiperda in eastern China, connecting the year-round breeding area in South China and the major maize planting area in Northern China. Understanding the migration dynamics in this area is crucial for the forecasting and controlling of this pest throughout the country. Based on three years’ data (2019–2021) in the Yangtze Delta, the migration timing, migration pathway, the source area of immigrants and the potential landing area of emigrants were identified. It revealed that S. frugiperda mainly migrated into the Yangtze River Delta in May and June, and their progenies further migrated northward to Northern China mostly in July and August. The results of this paper will be helpful to further understand the migratory rules of S. frugiperda, and to provide a theoretical basis for pest forecasting and pest control. ABSTRACT: The Yangtze River Delta, located in East China, is an important passage on the eastern pathway of the northward migration of fall armyworm Spodoptera frugiperda (Smith) in China, connecting China’s year-round breeding area and the Huang-Huai-Hai summer maize area. Clarifying the migration dynamics of S. frugiperda in the Yangtze River Delta is of great significance for the scientific control and prevention of S. frugiperda in the Yangtze River Delta, even in the Huang-Huai-Hai region and Northeast China. This study is based on the pest investigation data of S. frugiperda in the Yangtze River Delta from 2019 to 2021, combining it with the migration trajectory simulation approach and the synoptic weather analysis. The result showed that S. frugiperda migrated to the Yangtze River Delta in March or April at the earliest, and mainly migrated to the south of the Yangtze River in May, which can be migrated from Guangdong, Guangxi, Fujian, Jiangxi, Hunan and other places. In May and June, S. frugiperda migrated further into the Jiang–Huai region, and its source areas were mainly distributed in Jiangxi, Hunan, Zhejiang, Jiangsu, Anhui and Hubei provinces. In July, it mainly migrated to the north of Huai River, and the source areas of the insects were mainly distributed in Jiangsu, Anhui, Hunan, Hubei and Henan. From the south of the Yangtze River to the north of the Huai River, the source areas of S. frugiperda were constantly moving north. After breeding locally, S. frugiperda can not only migrate to other regions of the Yangtze River Delta, but also to its surrounding provinces of Jiangxi, Hunan, Hubei, Henan, Shandong and Hebei, and even cross the Shandong Peninsula into Northeast China such as Liaoning and Jilin provinces. Trajectory simulation showed that the emigrants of S. frugiperda from the Yangtze River Delta moved northward, westward and eastward as wind direction was quite diverse in June–August. This paper analyzes the migration dynamics of S. frugiperda in the Yangtze River Delta, which has important guiding significance for the monitoring, early warning and the development of scientific prevention and control strategies for whole country.