Growth performance and dynamic copper accumulation in tissues of black soldier fly (Hermetia illucens) larvae under copper exposure

To figure out the copper metabolism features in vivo and evaluate the potential risk of copper residue in tissues of black soldier fly larvae (BSFL) and their by-products, the effects of oral copper exposure of 0, 50, 500 and 1000 mg/kg (Control, Cu50, Cu500 and Cu1000) on growth performance and dynamic copper accumulation in the fat body, cuticle of BSFL and the rearing residue were investigated in a 12-days rearing trial. The results showed that, the body weight and length, and body protein content of BSFL were improved by exposure to 50 mg/kg copper, but reduced by exposure to 500 and 1000 mg/kg copper, as well as that of the pre-pupa rate. Under the copper exposure of 500 and 1000 mg/kg, the copper concentrations in the larval fat body were high at the early developmental stage, but sharply reduced to be 8.1 ± 0.3 mg/kg within 12 days with no significant differences among groups. Similarly, the copper concentrations in the cuticle also decreased rapidly to be 46.3 ± 2.9 and 91.3 ± 9.4 mg/kg in the Cu500 and Cu1000 groups within 12 days, but they were significantly higher than those of the control (8.1 ± 0.3 mg/kg) and Cu50 (10.1 ± 1.1 mg/kg) groups. The linear regression analysis between copper exposure doses and copper concentrations in the rearing residues indicated that the latter are dose- and time-dependent. Overall, the growth performance and body protein content of BSFL were improved by low copper exposure, but reduced by high copper exposure. The oral copper could be excluded from larval fat body and cuticle rapidly, and be largely accumulated in the rearing residues. Therefore, little risk of copper residue in the main tissues of post larvae or pre-pupae of black soldier fly (BSF), but higher risk of it in the rearing residues could be anticipated. Our results provide valuable information for safety assessment of copper residues in BSF products and by-products.