| To clarify the cold tolerance of Spodoptera frugiperda (Fall Armyworm), this study assessed the survival of larvae and pupae under different low-temperature regimes (constant and fluctuating temperatures), providing a scientific basis for predicting the overwintering distribution of this pest. In constant temperature experiments, third-instar and fifth-instar larvae were subjected to short-term low-temperature stress at 0℃, ?2℃, ?5℃, and ?10℃, with mortality recorded at 0.5, 1, 2, 3, 6, 12, 24, and 36 h. Additionally, 4-day-old pupae were treated at 6℃ and 10℃ for 3 d and 5 d to observe eclosion rates. In fluctuating temperature experiments, based on baseline temperatures of 6℃ and 10℃, diurnal temperature fluctuations of ±2℃, ±4℃, and ±6℃ were set. Fifth-instar larvae and 4-day-old pupae were subjected to stress for 0, 5, 10, 15, 20, 25, and 30 d, with larval mortality, pupation rate, and pupal eclosion rate recorded. The results showed that under short-term low-temperature stress, the mortality of larvae and pupae gradually increased with the decreasing temperature and prolonged exposure. After 36 h, larvae survived at 0℃ but all died at ?5℃ and ?10℃. Pupae eclosed normally under constant temperatures of 6℃ and 10°C, but the eclosion rate decreased with prolonged low-temperature exposure. Under long-term fluctuating low-temperature conditions, fifth-instar larvae survived for 30 d at 10℃ with a mortality rate ranging from 21% to 57%. At 6℃, larvae survived for 21 days, but pupae failed to eclose normally under any fluctuating temperature treatment. In summary, S. frugiperda populations may overwinter as fifth-instar larvae and pupae within the temperature range of 6℃ to 10℃, but cannot survive in regions below 6℃. The results of this study provide a scientific basis for predicting the distribution and spread trend of S. frugiperda and the prevention and control strategies. |
