Dietary Protein Levels in Isoenergetic Diets Affect the Performance, Nutrient Utilization and Retention of Nitrogen and Amino Acids of Hermetia illucens (L.) (Diptera: Stratiomyidae) Larvae

Abstract

Black soldier fly, H. illucens larvae, efficiently convert low-value organic substrates into high-value products, offering solutions to global challenges in sustainable food production and biotechnology. This study investigated the impact of dietary protein levels (10%, 14%, 16%, and 20% crude protein, CP) on BSFL growth, nutrient utilization, and energy retention using isoenergetic diets (18.5 ± 0.3 MJ/kg dry matter) under commercial-scale conditions. Larvae were harvested after 8 days of feeding, with 5 replicates per treatment. Optimal growth performance and feed conversion ratios were observed in larvae fed 14% CP diet, with a quadratic relationship between dietary CP and biomass gain (p < 0.001, R2 = 0.870). Ash and calcium deposition peaked in CP20-fed larvae and were lowest in CP14-fed larvae. Phosphorus and glucosamine deposition remained unaffected, while chitin deposition correlated positively with larval weight. Nitrogen and amino acid retention were highest in CP14-fed larvae but reduced in CP20-fed larvae (p < 0.001, R2 = 0.573–0.902). CP10-fed larvae showed impaired growth and nitrogen deposition but increased fat deposition. These findings establish the CP14 diet as the optimal formulation for scalable BSFL production, providing critical insights into dietary protein effects on BSFL physiology and enabling the development of efficient feeding strategies for industrial-scale farming.