Characteristics and seasonal variation of fall armyworm migratory behavior in their year-round breeding areas in South China

BACKGROUNDThe occurrence of migratory takeoff behavior is the essential first step for long-distance migration of insects. However, its characteristics, frequency of occurrence, and the identity of environmental and physiological factors influencing this process remain largely unknown.RESULTSWe investigate the global pest fall armyworm (FAW, Spodoptera frugiperda) as an exemplar species to investigate the behavioral traits associated with migratory takeoff of nocturnally migrating moths in year-round breeding areas. Our studies of FAW were carried out in Yunnan (2020-2022) and Hainan (2023) provinces of South China. Most migratory FAW moths were observed to takeoff at the age of Day (D)1-3, with the highest migratory proportion on D2, whereas mating behavior mostly happened during the first half night on D1. Typically, the migratory individuals took off within 40 min after sunset when the illumination fell below 2.7 lx, reaching its peak within 15 min. The optimal conditions for their takeoff are warm and dry weather with gentle winds. Yunnan and Hainan field populations showed a similar seasonal pattern in their migratory proportion, with the highest proportion in spring, and then decreasing as the seasons progress. Additionally, FAW moths emerging from caterpillars fed on maize plants at V14-R1 stages showed a higher migratory proportion than those from larvae fed on maize plants at other growth stages. Compared with nonmigratory individuals, migratory ones had slightly longer forewings (marginally significant) and flew faster, with higher wingbeat frequency, but other morphological characteristics and flight parameters were similar.CONCLUSIONThe study of FAW moths in Yunnan and Hainan from 2020 to 2023 found that migratory moths take off under specific conditions and show a seasonal pattern, with those from certain maize stages having higher migratory proportion, longer forewings and faster flight. These findings advance our understanding of the migratory takeoff behavior of FAW and, thus, provide a basis for the accurate prediction and management of the migratory dynamics. (c) 2025 Society of Chemical Industry.