Antioxidant response fail to rescue growth of Hermetia illucens L. larvae induced by copper accumulated during long-term exposure

Antioxidant indices and hemocytes apoptosis in the 6th instar larvae of Hermetia illucens., and their correlation with larval growth were evaluated by exposing larvae to different concentrations of Cu²⁺ for 1, 3 and 5 generations. Cu²⁺ accumulated in larval hemolymph showed significant dose-dependent relationship with Cu²⁺ concentrations in diets within a generation. Larval growth was only promoted after low concentrations of Cu²⁺ exposure for 1 generation, while seriously affected after high concentrations of Cu²⁺ exposure. Though total antioxidant capacity activity in larval hemolymph in treatment groups was all higher than that in control, it was increased at lower levels of Cu²⁺, while decreased with increasing Cu²⁺ concentrations at higher levels of Cu²⁺ exposure. The catalase (CAT) activity and metallothioneins (MTs) levels were also characterized as improved at lower levels of Cu²⁺, and inhibited at higher levels of Cu²⁺ exposure. However, CAT activity and MTs levels at higher Cu²⁺ treatments were significantly lower than that in control. Apoptosis rate of hemocytes was increased with increasing Cu²⁺ concentrations. Annexin V - fluorescein isothiocyanate (FITC)/ propidium iodide (PI) staining was in accordance with the results exhibited in flow cytometer. Results from transmission electron microscope and comet assay further confirmed that membrane blebbing, nuclear condensation, and DNA fragmentation were gradually apparent with increasing Cu²⁺ concentration. All parameters in different generation had similar dose-dependent trends, but the effects were strongest in the fifth generation. This study indicated that at some extent growth of H. illucens were associated with antioxidant responses and apoptosis induced by Cu²⁺.