Seasonal variability of the HO.RE.CA. food leftovers employed as a feeding substrate for black soldier fly (Hermetia illucens L.) larvae and effects on the rearing performance

The SCALIBUR project (Horizon, 2020) aimed to explore innovative solutions, including the use of black soldier fly larvae, for the bio-urban waste management. This research work describes the evaluation of the variability in water, proteins, fat, ashes, and carbohydrates present in the HO.RE.CA. food leftovers which were withdrawn from a local canteen over a 12-month period and the relationship with (i) the growth parameters of the larvae, (ii) the percentage of substrate reduction and the percentage of frass separated through the mechanical sieve at the end of the rearing process. HO.RE.CA. food leftovers are overall a suitable feeding substrate for larval rearing. Water contained in the HO.RE.CA. food leftovers was sufficient for larval rearing without resorting to further addition. As for water content, a seasonal trend was not observed, on the contrary, it was proved to be totally random. However, high amount of water (>80%) was correlated with higher larval mortality rate. The larval weight was significantly correlated to the amount of protein (r = 0.80; p ≤ 0.001) present in the substrate, and to a lesser extent to the amount of fat (r = 0.43; p ≤ 0.05). The feed conversion rate and bioconversion rate were both in agreement with literature data. The statistical test did not show any significant correlation between the amount of water contained in the initial fresh HO.RE.CA. food leftovers and the percentage of substrate reduction and the percentage of frass separated through the mechanical sieve at the end of the rearing process.