Metabolic adjustment of the larval fat body in Hermetia illucens to dietary conditions

The black soldier fly (BSF), Hermetia illucens, has great economic importance because of its ability to degrade a wide variety of organic products, including vegetable waste. The conversion of organic waste into valuable nutrients, that can be isolated from larvae and prepupae, is a widely exploited strategy to produce protein for animal feed and, consequently, comprehending the mechanisms that regulate nutrient accumulation in this insect could improve the production of insect-derived meal quantitatively and qualitatively. Since the fat body participates in metabolizing proteins, fat, and sugars in insects, detailed knowledge of this organ and of its modifications in relation to insect food intake could provide interesting clues about the nutritional value of the larvae, a fundamental aspect from an applied perspective. To this end, we performed a morphofunctional and molecular characterization of the fat body of sixth instar H. illucens larvae reared on different food substrates, focusing on markers related to nutrient accumulation. We demonstrate that a protein-poor diet affects both lipid and protein accumulation in fat body cells as well as the expression of key genes involved in these metabolic processes. Our study not only represents the first characterization of the larval fat body in this insect, but also confirms the central role of this organ in nutrient accumulation and substantiates the hypothesis of producing larvae with higher nutritional value by manipulating the diet.