Feasibility of soilless substrate systems supplemented with black soldier fly frass for sustainable mushroom cultivation

The rising cost and limited availability of sawdust have driven interest in alternative substrates for mushroom cultivation. Black soldier fly larvae (BSFL) frass is a nutrient-rich byproduct of insect farming that could serve as a low-cost supplement, however, its effective incorporation requires a suitable substrate matrix. This study evaluated BSFL frass supplementation in a soilless, inert substrate system composed of perlite (P), vermiculite (V), and pumice stone (PS) for cultivating pearl oyster mushroom ( Pleurotus ostreatus ). Substrate formulations with increasing frass dosages were developed and assessed for mycelial colonisation, harvest period, yield performance, substrate efficiency, and fruiting-body nutritional quality. Low frass inclusion corresponding to 0.13% nitrogen improved colonisation (up to 13.11 cm 2 /day) and shortened harvest period to 24 days, whereas higher nitrogen levels (>0.57%) suppressed growth and resulted in cultivation failure. Improved aeration and moisture retention associated with the low-bulk-density soilless matrix were identified as key contributors to successful colonisation. The optimal formulation was a 2:1:2 (P:V:PS) mix supplemented with frass at 0.13% nitrogen. Compared with commercial supplemented sawdust substrate and frass-amended sawdust matrix, the frass-amended soilless substrate achieved a comparable effective yield but lower biological efficiency (BE) and a longer harvest period than the commercial control, while outperforming frass–sawdust substrate in yield and efficiency. Mushrooms grown on frass-based substrates showed approximately 10% higher protein content than those from the commercial substrate. Overall, BSFL frass is a promising supplement for soilless mushroom cultivation and supports circular waste to food pathways, though further optimisation is needed for commercial scalability. • BFSL frass served as an alternative supplement for soilless mushroom cultivation. • Low frass (0.13% N) enhanced mycelial colonisation and reduced harvest period. • High frass (>0.57% N) inhibited mycelial growth and fruiting body formation. • Higher protein (based on dry matter basis) was observed in frass cultivated mushroom. • Soilless substrates enhance aeration, moisture retention to support mycelial growth.