Conversion of vegetable residues and wheat straw by black soldier fly larvae: growth, chemical composition, and gut microbiota

Abstract China generates about 240 million tons of vegetable residues and 1 billion tons of crop straw annually. This study evaluated the performance of black soldier fly larva (BSFL) on three vegetable residues (cabbage (CA), celery (CE), and white radish (WR)), either alone or mixed with wheat straw (3:1, 1:1 w/w). The results showed that CA residue alone supported the best larval growth (maximum individual weight: 76.0 mg, 72.0% of the standard diet (SD)). But straw addition significantly reduced larval weight and survival ( P < 0.05). Vegetable residues significantly enhanced straw degradation compared to straw-only treatments, as evaluated by X-ray diffraction and scanning electron microscopy. BSFL reared on vegetable-containing substrates showed comparable dry matter, crude protein, and ash to the SD, while having lower crude fat (19.2–19.9% vs. 21.8%). High-throughput sequencing of the larval gut microbiota showed that straw supplementation significantly increased gut microbial richness and upregulated the abundance of methyl-accepting chemotaxis protein KO3406. At the phylum level, Firmicutes, Actinobacteriota, and Proteobacteria dominated across all treatments. In addition, vegetable–straw mixtures promoted seed germination and root development. These findings offer a practical co-management strategy for high-moisture vegetable residues and lignocellulosic agricultural residues, providing new microbial insights into substrate adaptation in BSFL.