The serine protease Brachyuran is highly expressed in the posterior midgut of the black soldier fly, Hermetia illucens, during the processing of horse droppings

Objective Livestock droppings cause some environmental problems, but they have the potential to be used as effective biomass resources. The black soldier fly (BSF), Hermetia illucens (Diptera: Stratiomyidae), is suitable for the efficient processing of livestock droppings. By using BSF larvae for the disposal of livestock droppings, we can obtain two valuable products: protein resources and organic fertilizer. However, there is not enough research on the digestive enzymes suitable for processing livestock droppings. Here, we aimed to construct an efficient BSF processing system using livestock droppings, and we explored the digestive enzymes involved in this process. Results First, we investigated the characteristics of transcripts expressed in the midgut of H. illucens and found that immune response-related genes were expressed in the midgut. Then, we investigated digestive enzymes and identified a novel serine protease, HiBrachyuran , whose mRNA was highly expressed in the posterior midgut when H. illucens larvae fed on horse droppings. Despite the low protein content of horse droppings, larvae that fed on horse droppings accumulated more protein than did those in the other groups. Therefore, HiBrachyuran may contribute to digestibility in the early stage of protein degradation in H. illucens larvae fed on horse droppings.