Combined transcriptome and metabolome analyses provide insights into host adaptation mechanism of Spodoptera frugiperda to cruciferous vegetables

The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), is a worldwide migratory pest that inflicts considerable harm on numerous economically vital crops. Cruciferous vegetables, specifically pakchoi (Brassica campestris L.) and purple cabbage (Brassica oleracea L.), are prominent cash crops in southern China; nevertheless, the suitability of larvae for these crops remains undetermined. This study examined the performance of S. frugiperda when fed B. campestris and B. oleracea leaves. Histopathological investigation indicated no significant alteration in the structure of the larval midgut in the B. campestris treatment group; however the B. oleracea treatment adversely affected the larval midgut structure. The activities of GST, CarE, AMS, and LPS in larval midguts from various treatment groups were studied. Comparative transcriptome analysis revealed that 793 and 3375 differentially expressed genes (DEGs) were found in the samples treated with B. campestris and B. oleracea, respectively, in comparison to the control. The DEGs that encode detoxification and digesting enzymes were subjected to additional analysis. Metabolome analysis identified 295 and 241 differential metabolites (DEMs) in the samples treated with B. campestris and B. oleracea, respectively, in comparison to the control group. KEGG pathway enrichment analysis indicated that taste transduction and purine metabolism were significantly influenced by these two cruciferous vegetables. The comprehensive analysis of these two omics datasets revealed that the metabolic pathways of amino acids, carbohydrates, and lipids were collectively enriched with DEGs and DEMs. Our findings establish a basis for subsequent investigations into the fitness mechanisms of S. frugiperda on cruciferous vegetables.