Fungus Residue Amendment and Fermentation Enhance Black Soldier Fly Bioconversion of Fox and Raccoon Dog Manure into Quality Larval Meal and Frass Biofertilizer

Rearing black soldier fly (BSF) larvae on fox and raccoon dog manure (FRM) is an effective approach to both mitigate environmental pollution and produce high-quality feed and biofertilizer. However, FRM is rich in complex organic matter, has high ash content, an extremely high viscosity, and harbors pathogens, which lead to very low larval survival and pupation rates. To address these issues, this study introduced fungus residue (FR) amendment and fermentation. Compared with sole FRM (pupation rate 48.89%, survival rate 5.00%), the 1:1 FR : FRM mixture significantly improved pupation rate to 73.51% and survival rate to 61.35%, and fermentation of the 1:1 mixture further increased larval weight (0.0936 g) and survival rate (90.69%). BSF larval meal from the combined treatment contained 12.2% protein, 15.9% fat, and 31.95% total amino acids, with no detectable heavy metals. BSF frass had 68.7% organic matter and total NPK of 10.48%. When applied as a biofertilizer for Chinese cabbage, the 25% frass and 75% garden soil treatment gave the best results, with a germination rate of 98.33%, single-plant fresh weight of 515.11 g, and chlorophyll content of 2.52 mg/kg. In conclusion, FR-amended and fermented FRM is a suitable BSF rearing substrate, offering a sustainable solution for FRM management.