Effects of low-temperature stress on cold-resistant substances and gene expression in Spodoptera frugiperda (Lepidoptera: Noctuidae)

Abstract: The fall armyworm Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) is a major agricultural pest. Low temperature is an important factor that limits S. frugiperda survival and reproduction. In this study, the physiological cold tolerance indexes of S. frugiperda larvae from October 2022 to February 2023 were investigated. The expression levels of EOL and EPL, two lipid metabolism genes, in different developmental stages were studied under 5°C and 10°C stress. The results showed that the antifreeze protective substances of S. frugiperda differed significantly between different months. The water contents were the lowest in January and the highest in October. Lipid contents were the highest in December and January, trehalose and protein contents were the highest in December, and glycerol contents were the highest in January. The contents of lipid, proteins, trehalose, and glycerol were the highest in the 6th instar larvae, whereas the water contents did not differ. The expressions of EPL and EOL were either activated or inhibited in different developmental stages and tissues under cold stress. The expressions differed between the two temperatures (5°C and 10°C). The mRNA levels of EOL and EPL reached the highest silencing efficiencies of 60.76% and 82.53% at 24 h, respectively. Additionally, EOL and EPL silencing significantly decreased the lipid contents and survival rates of S. frugiperda after cold stress. These results indicate that the contents of antifreeze protective substances and relative genes could change to adapt to cold stress, but these changes differed between the stages and temperatures.