Effects of continuous and transgenerational rearing in peanut leaves on the performance and enzyme activity of <i>Spodoptera frugiperda</i> (Lepidoptera: Noctuidae)

The invasive fall armyworm (FAW), Spodoptera frugiperda, is a polyphagous pest that significantly threatens crops worldwide. FAW may undergo adaptation, enhancing its ability to infect specific plant hosts. However, there is limited knowledge on this topic. After 8 generations of constant rearing on peanut leaves, the performance and enzyme activities of FAW were investigated in this study. Compared to FAW fed on the peanut cultivars 'Fuhua 8' and 'Quanhonghua 1' for 2 generations, those grown on leaves for 5 to 8 generations had significantly shorter pre-adult development times and total preoviposition periods. Fecundity also increased significantly, resulting in an overall improvement in population fitness as measured by demographic parameters. However, the F2 generation of FAW fed on corn leaves outperformed the F8 generation of FAW fed on peanut leaves. In the F2 generation, the FAW peanut population exhibited 30-55% supernumerary larval molts, which decreased substantially in the F5 and F8 generations. Notably, supernumerary larval molts displayed pupation and emergence rates comparable to normal larvae, regardless of the peanut cultivar or rearing generation. The activities of lipase and acetylcholinesterase increased significantly from the F2 to F8 generations, showing substantial negative and positive correlations with larval development time and fecundity, respectively. In conclusion, FAW demonstrated inferior performance on peanut leaves compared to corn leaves, despite its performance was significantly improved after 5 to 8 generations of acclimation. These results suggest that corn will continue to be the primary target crop for FAW in China.