Abstract: Mythimna separata (Walker) is a vital pest insect in China. In order to identify the parameters of seasonal migratory behavior of M. separata (Walker) in Northeast China, long-term observation was carried out by vertical-looking radar (VLR) and light traps in Jilin province in 2005, in combination with analysis of large-scale wind systems and trajectory simulation based on GIS. The results showed that migration of M. separata moths only occurred on a few nights during each of three distinct migration periods; they flew at obviously different altitudes depending on season and time of night, and their migratory behavior was significantly influenced by meteorological conditions, especially the large-scale atmospheric circulation. The long-distance migration was windborne, and flights of M. separata moths could be observed throughout the night. The flying altitude in spring was mainly 300-600 m, while that in autumn was relatively low, mainly below 500 m. Radar echoes in summer were obvious in layers, indicating that the migrants were sometimes concentrated into two or more layers, mainly in 500 and 700 m, with a maximum height of up to 1 000 m. Trajectory analysis showed that on May 29 and June 1, M. separata populations flying over the radar station originated from the southwest, probably from Shandong province. In mid-July, however, these populations were locally landed and showed relatively short-distance dispersal under the influence of convective weather. On September 11, M. separata populations originating from the Hulun Buir region of Inner Mongolia were observed to fly on northwesterly winds to the southeast of Jilin province. The results provided technical support for the effective prevention and control of armyworm in Northeast of China.

Key words: Mythimna separata, migration, radar observation, trajectory analysis, verticallooking radar (VLR), light trap, population source