Guo_2026_Insects_17_

Diet plays a critical role in shaping the composition of gut microbiota in insects. Samia ricini, an economically important Lepidoptera insect, is a polyphagous herbivore that offers a useful model for studying dietary effects on the animal gut microbiome. Here, we fed S. ricini larvae with different food plants, Ricinus communis, Ailanthus altissima, and Manihot esculenta leaves to investigate how host plant species influence growth performance, digestive enzyme activities, and the gut microbial community. Our results showed that the Ricinus group exhibited better growth performance. Regarding digestive enzymes, the midgut lipase activity was significantly higher in the Ricinus group than in the Ailanthus group, while no significant differences were observed in alpha-amylase, cellulase, or trypsin activities among the three groups. Compared to the Manihot group, the Ricinus group showed increased bacterial richness, while the Ailanthus group showed increased bacterial diversity. beta-diversity analysis further revealed distinct microbial community structures among all three dietary groups. Specifically, Acinetobacter, Mammaliicoccus, Roseateles, Methylobacterium, Agrobacterium, Faecalibacterium, and Segatella were the dominant bacterial genera. Functional prediction revealed that gut microbes enriched in the Ricinus group were associated with terpenoid/polyketide metabolism, xenobiotics biodegradation, and glycan biosynthesis, whereas those involved in carbohydrate metabolism and biosynthesis of other secondary metabolites were higher in the Manihot group. Spearman correlation analysis indicated that Methylobacterium, Methylorubrum, and Agrobacterium were significantly positively correlated with larval weight, while Staphylococcus and Cyanothece_PCC-7424 exhibited negative correlations. Collectively, these findings suggest a potential association between different plant-derived diets, gut microbiota composition, and host growth performance, highlighting the pivotal role of diet in shaping insect gut microbial communities.