Molecular and functional characterization of Hermetia illucens larval midgut

The increase in global demand for meat and the management of organic waste are huge global issues. In addition to policies to contain the excessive meat consumption and the production of food waste, a possible perspective is to consider insects as agents for organic waste reduction and as source of protein for monogastric feed production. The larvae of Hermetia illucens (Diptera: Stratiomyidae) are good candidates for bioconversion of vegetal waste and feed production because they grow on different organic substrates and the dry-matter of the prepupa contains a very high percentage of protein with high nutritional value. The study of H. illucens midgut physiology is essential to understand the extraordinary feeding plasticity of this insect and to best exploit this ability. We characterized the digestive enzymes involved in the initial phase of digestion in the three regions of the midgut (anterior, middle and posterior). The proteolytic activity was assayed using chromogenic substrates and specific inhibitors. The total proteolytic activity is highest in the posterior midgut and the major activity is due to serine proteases. We measured the activity and the transcript levels of the two main serine proteases involved in insect digestion: trypsin-like and chymotrypsin-like proteases. Moreover, we determined the total amylolytic activity and the highest value was recorded in the anterior midgut. Thanks to our data, we propose the first model of the functional activity of H. illucens midgut. This work was supported by Fondazione Cariplo (Insect bioconversion: from vegetable waste to protein production for fish feed, ID 2014-0550).