Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), has become an important pest in Chinese agricultural systems since its invasion on 11 December 2018.  After its establishment, FAW months in the year-round breeding region have become the main source population migrating to other areas in China.  Field investigations were conducted in tropical and subtropical regions to improve understanding of its year-round breeding area in China.  The results showed that FAW larval density was significantly correlated with the seasonal temperature of the location surveyed.  The FAW larvae maintained a high density in the tropical area and were frequently found in sites of the south subtropical region, but were absent from the north subtropical region and the northern part of the central subtropical region.  These results indicated that FAW can reproduce annually in the tropical and south subtropical regions of China, including Hainan, Taiwan and the southern area of Fujian, Guangdong, Guangxi, Guizhou, and Yunnan.  Hence, great effort should be made to monitor and control FAW in the year-round breeding region to suppress the population density of this area and to reduce migration of moths into northern parts of China.  This study clarifies the occurrence area of the pest in winter in China and provides much valuable information for its population forecasting and management.

fall armyworm ,  temperature ,  year-round breeding region ,  tropical region ,  subtropical region