Effect of heavy metal on growth of black soldier fly larvae (Hermetia illucens): Accumulation, excretion and gut microbiome

Abstract

The larvae of black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae), are an excellent source of feed for animals and have emerged as a promising candidate for waste disposal. The larval growth can be impacted by the intake of heavy metals. However, the underlying mechanism for metal tolerance of the gut microbiome is still poorly understood, as well as how heavy metals, especially in combination, affect the communities of bacteria in the larval gut. Therefore, in this study we focus on how Cu and Zn affect larval growth and gut microbiome, as well as how bioaccumulated heavy metals are distributed in larval residues and bodies. The larval biomass growth was both significantly improved and inhibited by exposure to low and high Cu and Zn concentration, respectively, including in combination. The amount of accumulated Cu and Zn in larval residues and bodies significantly increases as the exposure concentration is increased. In larval bodies, Zn was more likely to be accumulated (57.2%–78.5%) than Cu (<40%). More importantly, the larval gut microbiome was found to be remarkably altered by Cu and Zn exposure, particularly for species of the phyla Actinobacteria, Bacteroidetes, and Firmicutes. In addition, with the exception of the Cu at 400 mg kg⁻¹ exposure, the diversity and complexity of the gut bacterial community significantly decreased. Functional genes related to heavy metal resistance and transport, such as pcoB, pcoD, copC, pccA, ABC.ZM.S, and yahk, were clearly enriched in the larval gut, which may help to partly account for the ability of black soldier fly larvae to tolerate metals.