Density and substrate-dependent performance of black soldier fly larvae, Hermetia illucens (Diptera: Stratiomyidae) reared on locally available biowastes in Nepal: Effects on growth, bioconversion, and nutritional composition

Black soldier fly (BSF) larvae are a promising alternative nutrient source for animal feed, yet operational guidelines for larval density optimization across diverse waste streams available in Nepal have not yet been established. This study evaluated substrate-specific density effects to identify rearing strategies for valorizing locally available biowastes in Nepal. Five-day-old larvae were exposed to vegetable waste, chowmein waste, and chicken feed (control diet) as feeding substrates at four larval densities (1, 3, 5, and 7 larvae/cm 2 ) at a uniform feeding rate (25 mg dry matter/larva/day) across the treatments. BSF prepupal weight decreased with increasing density in chicken feed but increased with density in vegetable and chowmein wastes. Larval survival increased with density in chowmein waste but declined at higher densities in vegetable waste, while bioconversion efficiency showed the opposite pattern. The larval protein content under chowmein waste was generally low, whereas higher larval protein content was obtained under vegetable waste, particularly at lower densities. Conversely, larval fat content was lower under vegetable waste at lower densities but increased with higher larval densities. The results suggest that waste utilization and the nutritional potential of BSF larvae are determined by the density-dependent responses across different substrates. Overall, when targeting BSF larvae as an alternative nutrient source for animal feed, food industry wastes are better utilized at higher larval densities, whereas fibre-rich substrates perform optimally at lower densities, highlighting the need for substrate-specific density strategies in BSF-based biowaste recycling systems. • Black soldier fly larvae efficiently recycle a diverse range of local biowaste. • Substrate–density interaction drives larval growth, survival, and nutrient profile. • Carbohydrate-rich substrates enhance the fat content of larvae. • Fibre-rich substrates at lower densities lead to high larval protein content.