Characterization of Hermetia illucens (Diptera: Stratiomyidae) larval midgut

Hermetia illucens (Diptera: Stratiomyidae) larvae are among the most promising agents for the bioconversion of organic waste into nutritionally valuable proteins for production of environmentally and economically sustainable insect-based animal feed. Despite the great interest toward this species, there is a lack of knowledge about its biology: in particular, a deep understanding of the physiology of the midgut, the main site of nutrient digestion and absorption, is essential to better comprehend the extraordinary dietary plasticity of the larvae and to better exploit their bioconversion ability. To overcome this gap, we performed an in-depth morphofunctional characterization of H. illucens larval midgut. Our results demonstrate that this organ is composed of three distinct anatomical regions with different features and midgut epithelium is formed by different cell types that accomplish different functions. The characterization of the activity of enzymes involved in nutrient digestion and their mRNA expression levels show that digestion is associated to specific regions of the midgut. Moreover, we investigated the impact of different feeding substrates on the morphology and physiology of larval midgut. Our data show a diet-dependent adaptation process of the midgut. This plasticity may be responsible for the ability of H. illucens larvae to grow and develop on very different substrates. Finally, we analyzed the larval midgut microbiota. Our data demonstrate that both diet and midgut regionalization influence the microbial load and diversity. This work was supported by Fondazione Cariplo (Insect bioconversion: from vegetable waste to protein production for fish feed, ID 2014-0550).