Energy and nutrient composition and origin of common feed substrates for black soldier fly larvae determine their efficiency and life-stage-specific carbon dioxide and ammonia production.

Black soldier fly larvae (BSFL) are considered as sustainable source of protein due to their high substrate flexibility, but there is little data on greenhouse gas emissions during their production. Continuous gas exchange (CO2, O2, NH3) of BSFL under the influence of Gainesville fly diet (GD) and chicken feed diet (CF) of two different origins (2 x 2 design) on growth and body composition was analysed. The BSFL were transferred to the experimental substrates on day 5 after hatching (∼150 larvae/growth vessel, n = 6 replicates). Gas exchange of the BSFL was analysed from days 9-16 post-hatch. Larval amino and fatty acids composition was determined. The larvae achieved a higher final mass with CF and produced less CO2 than with GD (P < 0.0001). Compared to the substrates, all larvae accumulated methionine (> 10-fold), while the accumulation of crude protein, essential amino acids, and conjugated linoleic acid (C18:2 cis-9, trans-11) was higher in GD larvae than in CF larvae. The emissions of CO2 and NH3 relative to larval protein production were lower with CF than with GD, but total NH3 production was higher with CF (P < 0.0001). The CO2 emissions from the production of larval protein are lower than CO2 emissions from the production of protein in milk and broiler chickens, with the extent depending on the nutrient composition of the BSFL substrate. Life-stage-specific, continuous gas exchange profiles provide important insights for optimizing substrate nutrient composition, which is essential for sustainable and environmentally friendly BSFL production.