Performance and nutrient composition of black soldier fly larvae fed diets with various protein concentrations throughout the life cycle

Standardised rearing of black soldier fly (BSF, Hermetia illucens) larvae to utilise low-value organic substrates is gaining increasing interest in the context of sustainable animal production. The present study hypothesised that varying dietary protein concentrations would affect the growth performance and nutrient composition of BSF larvae across different life stages. To test this hypothesis, the effects of low (CPlow, 10% protein), medium (CPmed, 15% protein), and high (CPhigh, 20% protein) protein concentrations in isoenergetic diets were investigated on BSF growth from the juvenile to the adult stage, with six replicates per treatment. From day 10 (DOL, days-old larvae) onwards, larvae fed the CPlow diet had significantly lower live mass than those on CPmed and CPhigh diets, with reductions of 24 and 29% at 14 and 16 DOL, respectively, compared to CPmed-fed larvae (P < 0.05). This effect persisted through the prepupal and adult stages. Developmental time from egg to prepupa was shorter in the CPmed and CPhigh groups, resulting in larger prepupal and adult body sizes. Nutrient analysis revealed that larvae fed the CPmed diet had higher dry mass, protein, and amino acid mass at the prepupal stage compared to those on the CPlow diet, whereas fat deposition was increased in CPlow-fed larvae at certain developmental stages. This study demonstrates that both the nutrition of Hermetia illucens larvae and their life stage at separation are crucial for optimising their value as a feed source.