Biofortification of zinc and selenium in black soldier fly larvae reared on fortified agro-food by-products: growth performance and micromineral composition

This study investigates the effects of zinc (Zn) and/or selenium (Se) supplementation in the rearing substrate of black soldier fly larvae (BSFL) and their accumulation in larval biomass. BSFL were reared on five substrates: (1) control plant-based substrate (CTR; Gainesville diet); (2) okara and potato waste-based substrate (OP); (3) OP fortified with 150 mg/kg Zn (OP-Zn); (4) OP fortified with 0.3 mg/kg Se (OP-Se); and (5) OP fortified with 150 mg/kg Zn + 0.3 mg/kg Se (OP-SeZn). Larvae were maintained for ten days at 26 °C and 60% relative humidity, with five replicates per treatment. Survival rates were not affected by treatments (P>0.05). Final individual larval weights were similar across groups, except for OP-Zn, which showed lower weight. CTR larvae had significantly higher final biomass (P<0.05) than other groups. Larvae fed OP substrates fortified with Se and/or Zn had weights comparable to unfortified OP larvae, indicating that growth was primarily influenced by substrate type rather than mineral supplementation. OP-reared larvae had higher lipid content (P<0.05) and lower ash content (P<0.05) than CTR larvae. Fortification with Se and/or Zn increased the concentrations of these elements in BSFL, with the highest Se in OP-Se and the highest Zn in OP-SeZn, suggesting a synergistic effect of Se on Zn absorption. Results indicate that BSFL can be effectively reared on agro-food waste substrates and that Zn and Se supplementation produces “fortified” larvae with a nutritional profile consistent with average BSFL composition. Further research is needed to assess unintended metabolic effects of mineral fortification.