Black soldier fly (Hermetia illucens, BSF) larvae can utilise biowaste streams and convert them into high-quality larval biomass. However, the nutritional requirements of BSF larvae are largely unknown and remain to be identified to optimally use biowaste streams for BSF rearing. The current study thus investigated the optimal dietary protein to carbohydrate ratio for industrially reared BSF larvae for food and feed applications. In addition to a chicken feed control with a crude protein to non-fibre carbohydrate ratio (P:C) of 1:3, six isoenergetic and isolipidic experimental substrates were formulated with the P:C ratios ranging between 1:1 - 1:9. Each substrate was fed to triplicate groups of 5-days old larvae (n=10,000 per box) reared under commercial scale conditions for 11 days before harvesting. Highest overall performance was observed for larvae reared on substrates with P:C ratios between 1:2 - 1:3, corresponding to protein to energy ratios (P:E) of 11.2-14.4 g/MJ. Larvae reared on these substrates had the highest final yield, highest survival, and the lowest feed conversion ratio. Feeding the most protein-biased substrates (P:C ratios of 1:1 - 1:1.5) or the most carbohydrate-biased substrate (P:C ratio of 1:9) significantly lowered larval survival. Additionally, larvae fed a more carbohydrate-biased substrate resulted in a prolonged development time. In summary, the study found that P:C ratios of 1:2 - 1:3 (11.2-14.4 g/MJ P:E) were most optimal in terms of obtaining the highest larval yield and ensuring the best utilisation of feed resources for BSF production while meeting larval macro-nutritional requirements.
