Metagenomic analysis of gut bacteria in different developmental instars of Spodoptera litura

Spodoptera litura is a globally distributed agricultural pest across Asia and Australia (EPPO database, https://gd.eppo.int/taxon/PRODLI/distribution), whose gut microbiota significantly influences host feeding, digestion, immunity, and development. We used whole metagenomic sequencing to analyze the diversity and functional roles of gut bacteria at different developmental stages (eggs, first to sixth instar larvae, pupae, and adults). Findings revealed that Pseudomonadota predominated at the phylum level, with notable differences across instars: Bacillota was dominant in young larvae, whereas Verrucomicrobiota was added in older larvae, eggs, pupae, and adults. At the genus level, Pseudomonas dominated, Enterococcus was prevalent in larvae, and Piscirickettsia was prevalent in eggs, pupae, and adults. Metagenomic analysis identified numerous carbohydrate-active enzymes (CAZy database) aiding in plant cell wall polysaccharide digestion. Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated differential gene expression in metabolism and xenobiotic degradation across instars, with metabolic gene annotation levels declining as development progressed. Detoxification-related enzyme genes were predominantly expressed in early instar larvae and adults, uncovering microbial origins of these enzymes.IMPORTANCEOur study provides evidence that the gut microbiota significantly modulates the physiology of Spodoptera litura, with profound effects on its dietary habits, metabolic processes, and host fitness. Using whole metagenomic sequencing, we analyzed gut bacteria across different life stages. At the phylum level, Pseudomonadota and Bacillota were dominant, while at the genus level, Pseudomonas was the most abundant taxon. Metagenomic analysis identified enzymes aiding in plant cell wall digestion. Kyoto Encyclopedia of Genes and Genomes analysis showed varying gene expression in metabolism and detoxification, with higher expression in early instar larvae and adults. This research enhances understanding of S. litura gut microbiota-host interactions and supports novel pest control strategies targeting gut microbiota.