Background: Artificial diet-reared silkworms (Bombyx mori) exhibit reduced gut microbial diversity and impaired growth performance compared to mulberry-fed counterparts. While Bacillus subtilis is widely used as a probiotic in livestock and aquaculture, its impact on silkworms remains unexplored. This study investigates whether dietary supplementation with B. subtilis enhances larval development and elucidates the underlying mechanisms involving gut microbiota and metabolic pathways. Results: Supplementing artificial diets with B. subtilis (6 × 10⁵ CFU/g) significantly increased larval body weight by 9.1–22.1% during instar stages and improved feed utilization efficiency (FUE) by 4.09%–6.80% compared to controls. Cocoon quality metrics, including cocoon shell weight (+ 9.77% in females) and cocoon shell ratio (+ 6.56%), also improved. Mechanistically, B. subtilis did not colonize the midgut but transiently modulated gut physiology: it elevated midgut fluid pH and enhanced α-amylase, trypsin, and lipase activities. 16 S rRNA sequencing revealed reduced gut microbial diversity (Shannon index, P < 0.01) and shifts in community structure, with decreased abundances of potential pathogens (e.g., Pseudomonas) and commensals (e.g., Lactobacillus). Targeted metabolomics identified a 3.1-fold increase in phenylalanine levels in hemolymph, linked to upregulated aromatic amino acid metabolism pathways (KEGG). Dietary phenylalanine supplementation (0.4%) replicated B. subtilis-induced growth promotion, confirming its pivotal role in host-microbe interactions. Conclusions: B. subtilis enhances silkworm growth and silk production through multi-faceted mechanisms: reshaping gut microbiota composition, improving digestive enzyme activity, and elevating phenylalanine biosynthesis. These findings establish B. subtilis as a promising probiotic for optimizing artificial diet systems in Lepidoptera and highlight the central role of amino acid metabolism in insect-microbiome symbiosis.

There remains a significant gap in production performance and disease resistance between silkworms reared on artificial diets and those reared on mulberry leaves. This study aims to identify key differential proteins through proteomic analysis of the midgut of silkworms fed artificial diets compared to those fed mulberry leaves. Utilizing molecular docking technology, three anti-nutritional factors that consistently bind to the UGT40B4, UGT340C2, and UGT40A1 proteins were selected, and the differential expression of these UGT genes in response to various anti-nutritional factors was examined. The findings indicate that variations in feed significantly influence the expression of digestive, metabolic, and immune-related proteins within the silkworm midgut. Notably, the expression levels of the UGT40B4, UGT340C2, and UGT40A1 genes vary across different silkworm organs and developmental stages, reflecting their respective physiological roles. Furthermore, the effects of soybean isoflavone, tannic acid, and arabinoxylan on silkworm growth and cocoon quality were found to differ when these substances were incorporated into semi-synthetic feed. This research is anticipated to provide valuable insights for future studies on the role of UGT genes in the silkworm midgut and the formulation of artificial diets for silkworms.

The growing use of nanomaterials has sparked significant interest in assessing the insect toxicities of nanoparticles. The silkworm, as an economically important insect, serves as a promising model for studying how insects respond to harmful substances. Here, we conducted a comprehensive investigation on the impact of graphene oxide (GO) on silkworms using a combination of physiological and transcriptome analyses. GO can enter the midguts and posterior silk glands of silkworms. High GO concentrations (> 25 mg/L) significantly (P < 0.01) inhibited larval growth. Additionally, GO (> 5 mg/L) significantly reduced the cocooning rate, and GO (> 15 mg/L) hindered oviduct development and egg laying in silkworms. GO increased the reactive oxygen species content and regulated catalase activity, suggesting that it may affect insect growth by regulating reactive oxygen detoxification. The transcriptome data analysis showed that 35 metabolism-related genes and 20 ribosome biogenesis-related genes were differentially expressed in response to GO, and their expression levels were highly correlated. Finally, we propose that a Ribosome biogenesis-Metabolic signaling network is involved in responses to GO. The research provides a new perspective on the molecular responses of insects to GO.

As important silkworm varieties reared on artificial diet, Youshi No. 1 (YS) and Guangshi No. 1 (GS) showed remarkable differences in physiological characteristics. GS had significantly better performance than YS in body weight, cocooning ability, food intake, feed utilization efficiency, and digestive enzyme activities. We further performed metabolomics and 16S rRNA high-throughput sequencing to analyze their metabolic profiles and midgut microbiota. More than 40 differential metabolites were screened out, and four metabolic pathways related to feeding divergence were determined via KEGG enrichment, among which L-valine was enriched in multiple pathways. Significant structural differences were also observed in midgut microbiota, and Bacillus was positively correlated with pantothenic acid and valine metabolism. These correlational results disclosed that differential metabolites and gut microbiota might underlie the phenotypic variations between the two varieties. Integrated analysis combined with functional verification experiments demonstrated that supplementation of 1% L-valine or specific Bacillus strains in an artificial diet was associated with the improvement of the growth performance, cocoon quality, and feed utilization efficiency of the YS silkworm variety.