From waste to wealth: how rearing substrates affect growth and nutritional value of black soldier fly larvae

Introduction Black soldier fly ( Hermetia illucens ) larvae have emerged as a promising sustainable solution for organic waste management and alternative protein production. However, their growth performance and bioconversion efficiency are strongly influenced by the rearing substrate. Methods This study investigated the influence of diverse organic rearing substrates on the larval development, biomass production and substrate conversion efficiency of the black soldier fly under controlled conditions at Assam Agricultural University, India, during 2023–2024. Eight substrates viz., vegetable, fruit, tea, vermicompost, papaya, potato + gram flour, corn and potato + corn wastes were evaluated in 2023 and 2024 to assess substrate-related developmental plasticity Results Larvae reared on vegetable waste (T 1 ) exhibited superior growth metrics, with maximum values of 20.25 mm (length), 5.18 mm (width) and 205.07 mg (weight) and the shortest development period (15 days). Vegetable waste consistently supported the fastest growth (15 days), highest biomass yield (205.07 mg/larva), and most efficient waste reduction (91.3%), demonstrating its potential for scalable insect farming systems. Substrate reduction and conversion efficiency were highest in T 1 , with a waste reduction index of 10.88% and diet reduction rate of 91.3% (Set B). Survivability peaked in the potato + corn substrate (T 8 ), reaching 84.43%, while protein content was highest in the same group (649.51 mg/g). The potato + corn mix showed the highest larval survivability (up to 84.43%) and protein content (649.51 mg/g), suggesting strong suitability for animal feed applications. Papaya-fed larvae recorded the highest crude fat content (8.99%), and saturated fatty acids, particularly lauric acid, dominated across all treatments. SEM confirmed the absence of morphological deformities across substrates. Results demonstrated that substrate composition and seasonal temperature regimes significantly affect BSF larval growth performance and waste valorization efficiency, with implications for optimizing insect-based bioconversion systems in sustainable feed and nutrient recycling applications. Seasonal temperature differences significantly influenced growth rates and substrate utilization, underscoring the importance of regional climate considerations in planning BSF production systems. Discussion These findings highlight the potential of integrating low-cost, organic waste streams into circular food systems via insect farming. Vegetable waste was the most suitable substrate for larval growth and waste valorization, whereas potato + corn waste showed potential for improving survival and protein enrichment. Optimizing substrate selection can enhance nutrient recovery, reduce organic waste volumes, and support climate-resilient, resource-efficient feed production aligning with sustainable agriculture and food security policies.