Fermented vegetable waste modulates gut microbiota and enhances bioconversion efficiency and nutritional quality of black soldier fly larvae (Hermetia illucens)

Abstract The adaptability of black soldier fly larvae (BSFL) to high-fibre, plant-derived waste is limited by poor nutritional quality and anti-nutritional factors (ANFs). To investigate how microbial pretreatment enhances this adaptability, we employed an aerobic-anaerobic sequential fermentation process using Bacillus subtilis , Limosilactobacillus reuteri and Lactiplantibacillus plantarum on a discarded vegetable mixture typical of plant-derived waste. Subsequently, we evaluated the changes in the nutritional composition of the substrate before and after fermentation and their effects on the growth performance, amino acid profile, fatty acid composition and gut microbiota of BSFL. The results demonstrated that fermentation significantly degraded crude fibre and ANFs such as glucosinolates, phytic acid and tannins, while enriching lysine, methionine, glutamic acid and butyric acid. Feeding trials showed that compared to the unfermented control, fermented feed significantly improved the prepupal weight, survival rate and bioconversion efficiency of the larvae while shortening the developmental period. In BSFL, the contents of lysine and methionine showed a slight increase, whereas the levels of 4-hydroxyproline, γ -aminobutyric acid, C16:0, C18:0, C18:1n-9, C18:2n-6 and C18:3n-3 increased significantly. Furthermore, fermented feed modulated the gut microbiota, reducing opportunistic pathogens ( Providencia , Fusobacterium ) and enriching beneficial Bacillus -related taxa ( Lysinibacillus , Bacillus , Paenibacillus , Brevibacillus ). Correlation analysis positively linked these taxa with improved growth and nutrient deposition. Functional prediction revealed sustained activity in amino acid and fatty acid metabolism pathways. Overall, microbial fermentation enhances BSFL adaptability to high-fibre waste, providing a reference for improving the bioconversion efficiency and nutritional value of BSFL through gut microbiota regulation.