An integrative framework linking substrate composition and physiological trade-offs to black soldier fly larval performance in organic waste valorization

Black soldier fly larvae (BSFL, Hermetia illucens) are increasingly used to convert organic wastes into insect biomass, yet their performance varies markedly among substrates. This variability limits the controllability of BSFL-based waste valorization systems. Conventional optimization efforts have largely emphasized macronutrient composition (e.g., protein and fat), while the effects of inorganic components and the physiological plasticity of the larvae have received little attention. To systematically elucidate the potential impact factors of this variability, we compiled and analyzed a global dataset comprising 905 rearing trials from 152 published studies. According to the results, high substrate ash content emerged as an overlooked constraint associated with reduced larval biomass and bioconversion efficiency. Larval performance was closely associated with the balance among substrate components. A Fat/Ash ratio >0.8 identifies as an empirical threshold associated with higher biomass accumulation, whereas a Protein/Fat ratio <2 was associated with higher bioconversion efficiency. We also observed a recurring trade-off between biomass accumulation and BSFL protein proportion. Under favorable conditions, larvae tended to prioritize biomass accumulation, whereas under stressful conditions, including ash-rich substrates, elevated temperature, and restricted feeding, they became smaller but maintained a relatively high body-protein proportion. Based on these statistical patterns, we propose an integrative framework linking substrate balance and larval physiological trade-offs. This framework summarizes empirical associations underlying performance variability and provides practical reference points for optimizing BSFL-based organic-waste-treatment systems.