Recycling of spent mushroom substrate and food waste: utilisation as feed materials for black soldier fly (Hermetia illucens (L.) Diptera: Stratiomyidae)

Spent mushroom substrate (SMS) is the organic material remaining after harvesting mushrooms. We evaluated the potential of using SMSs of four different edible fungi (Auricularia heimuer, Lentinus edodes, Pleurotus eryngii and Pleurotus citrinopileatus) as a food resource for rearing black soldier fly (Hermetia illucens) larvae (BSFL) and to decrease waste recycling and save conventional feed. The larval weight after being fed only on the SMS of L. edodes (68.8 mg), a mushroom with worldwide cultivation, was heavier than larvae fed entirely on P. eryngii SMS (38.3 mg). The L. edodes SMS was selected from the various SMS treatments and subsequently mixed with food waste in different percentages to make BSFL rearing medium. When L. edodes SMS replaced 0, 10, 20, 30, 40, 50, 60, 70, 80 or 90% of the food waste in the mixed feed treatments, the BSFL survival rates (99.2-100%) did not differ among the treatments. Body size or weight was reduced only when 90% of the food waste was replaced by L. edodes SMS. A higher percentage of BSFL, however, developed into prepupae (55.8, 46.7, 75.8%, respectively) when 20, 30 or 90% of the food waste were replaced by L. edodes SMS. Compared to BSFL fed entirely on food waste, larvae fed a mixed diet consisting of 30% L. edodes SMS and 70% food waste had a lower fat content (178.1 g/kg) and a higher content of crude ash (15.54%), crude fibre (17.81%), crude protein (38.13%), and moisture (10.08%). Although the aerobic plate count (9,200 cfu/g), total mould count (260 cfu/g), and the arsenic (0.1830 mg/kg) and lead (0.202 mg/kg) contents increased in larvae reared on the mixed diet, all were below the safety limit. Collectively, these results suggest that mixed diets consisting of 20-30% L. edodes SMS and 70-80% food waste have a great potential as a daily medium for culturing this important resource insect.