Tailored midgut gene expression in Spodoptera litura (Lepidoptera: Noctuidae) feeding on Zea mays indicates a tug of war

Spodoptera litura is a destructive lepidopteran generalist pest widespread in tropical and subtropical regions and causes huge yield loss by gregarious feeding on crop plants. During co-evolution, Zea mays (Var. African tall) has attained a well-crafted defence mechanism and can demote the performance of its invaders. When an insect feeds on a host/non-host plant, its digestive system needs to upregulate the first line of defence against a broad spectrum of antifeedants and toxins of host origin. To understand the molecular mechanisms underlying insect response to plant resistance factors, a comparative midgut transcriptome of Spodoptera litura fed on maize and control plants was investigated, which identified a total of 712 differentially expressed genes (DEGs), including 232 up-regulating and 480 down-regulating genes. Gene ontology, gene enrichment and pathway analysis revealed that upregulated genes are involved in carbohydrate metabolism, detoxification, defence, lipid metabolism, digestion, and signal transduction. In contrast, down-regulated genes were primarily linked to cytoskeleton, transport, signalling, carbohydrate and lipid metabolism, growth and developmental processes. The above results indicate an antinutritional stress on S. litura, which leads to a compensatory mechanism in the insect by enhanced digestibility and detoxification at the cost of growth and development. This study provides an overall understanding of the transcriptomic response of S. litura upon feeding on a suboptimal host. Nevertheless, our study forms the basis for future molecular studies on S. litura adaptation and may widen the scope for their management.