Upgrading ammonia-nitrogen from manure into body proteins in black soldier fly larvae

Nitrogen (N) losses via ammonia (NH3) emissions from manure is one of the main environmental burdens resulting from livestock production. Feeding manure to black soldier fly larvae (BSFL) is envisioned as a new circular strategy to recover manure-N, reduce its environmental impact, and upgrade it into insect proteins to be used in animal feed. However, so far, it remained unknown if BSFL could incorporate N from NH3 in manure into the larval body mass. Here, using the stable isotope 15N in NH3, we demonstrate that at least 13% of pig manure NH3-N can be incorporated into BSFL body mass. Within the larval body, the tracer was found in both insoluble and soluble nitrogen fractions, including proteins. We discuss interventions that could increase the incorporation of NH3-N into larval proteins and with that reduce NH3 emissions from manure. Our results provide the first reliable quantification of NH3-N assimilation in manure-fed larvae and contributes to quantifying the potential of BSFL for manure management, and as a circular protein source.