Abstract

This study investigated the feasibility and optimization strategies for utilizing black soldier fly larvae (BSFL) to bioconvert wheat straw into frass-based organic fertilizer. Different larval densities (200, 300, and 400 larvae per group) were tested to evaluate the conversion efficiency of wheat straw, larval growth performance, fertilizer characteristics of the frass, as well as its effects on soil microbiota and the growth of radish. The results demonstrated that BSFL effectively degraded wheat straw, with the group containing 300 larvae (TH group) exhibiting the best overall performance: a straw conversion rate of 42.9%, a significant reduction in cellulose crystallinity to 47.75%, an increase in total nitrogen content in the frass to 18.35 g/kg, and a germination index as high as 180%, indicating full maturation and the absence of phytotoxicity. Microbial community analysis revealed a significant increase in the abundance of cellulose-degrading taxa in the TH group frass, including the phylum Bacteroidota and genera such as Acinetobacter . Pot experiments further confirmed that radish seedlings amended with TH frass showed the best growth performance, with increased leaf number and enhanced abundance of beneficial microbial groups (e.g., Chitinophagaceae ) in the soil. This study provided an environmentally friendly novel approach for the efficient valorization of wheat straw, demonstrating that BSFL could not only process low-value agricultural waste but also produce high-quality organic fertilizer.