Review: A journey into the black soldier fly digestive system: From current knowledge to applied perspectives.

Recent literature on the black soldier fly (BSF) confirms the deep interest in this species for the bioconversion of organic waste, including challenging substrates that contain recalcitrant macromolecules, and highlights the growing trend in new applications for this insect. While protein meal remains the most prominent use of BSF larvae, emerging research is increasingly exploring alternative applications of biomolecules derived from these larvae, including proteins, lipids, chitin, and antimicrobial peptides. Moreover, the high feeding versatility of this insect is being recognised in fields beyond animal feed, such as bioremediation, where its potential ability to degrade contaminants can present significant ecological benefits. Although there is now widespread agreement that a thorough understanding of BSF biology is essential to enlarge the range of applications in which this insect may offer new sustainable solutions, studies on the digestive system are still limited and we are far from having a whole comprehension of the functional features of this complex structure. In fact, the gut is not only the core of the bioconversion process but also represents the first defence barrier against ingested pathogens, and due to the presence of a highly versatile gut microbiota, it may be a potential source of novel microbes and enzymes that could find application in various biotechnological sectors. This review aims to provide a comprehensive overview of the current knowledge on the BSF midgut -the central region of the gut responsible for nutrient digestion and absorption- in both larvae and adults, together with information about mouthparts and the organisation of the alimentary canal. Moreover, starting from the most recent studies on the midgut and its microbiota, we discuss implications for improving larval production, exploiting challenging substrates, and mitigating pollutants in contaminated biomasses.