Basil (Ocimum basilicum) growth and biochemical attributes are influenced by various black soldier fly (Hermetia illucens) larvae frass types

A major by-product of black solider fly larvae (BSFL) farming is the leftover mineral-rich ‘frass’, which shows promise as a soil amendment. The composition of BSFL frass, and potentially their efficacy, is influenced by the initial substrate. In this study, expired fish diets (EFD) or fruits/vegetables (FV) were used to produce BSFL frass, which were separately used as a soil amendment for basil versus basil that received weekly applications of a synthetic fertilizer (SF) (nitrogen, phosphorus, and potassium; 18-18-21). After five weeks, measurements of the sugar content, total phenol/antioxidant capacity, and mineral composition were determined. Basil heights became significantly taller with more biomass in SF (283 g) compared to the EFD frass treatment (115 g) but not the FV frass treatment (186 g). Compared with SF, basil leaves were significantly lower in manganese, calcium, zinc and iron in both frass treatments, but magnesium was significantly higher in the frass treatments. While soluble and insoluble sugar were significantly lower in both frass treatments (total of 26 and 13 mg/g in EFD and FV, respectively) compared to SF (43 mg/g), an opposite trend occurred with total phenol/antioxidant capacity. Results indicate deficiencies of some nutrients and more frequent applications of the BSFL frass might be necessary to overcome reduced production. Overall, FV frass enhanced basil production compared to EFD frass indicating that frass type influences plant growth.