Modulation of black soldier fly (Hermetia illucens) gut microbiota by agri-food processing by-products

Gut microorganisms are involved in many different aspects of insect physiology such as nutrition and development: an imbalance in their composition can negatively affect insect health and performance. Insect farming has emerged as a promising approach for the valorization of agri-food processing by-products, enabling both waste reduction and the sustainable production of alternative protein sources. Among candidate insect species, the Black Soldier Fly (BSF, Hermetia illucens) has received particular interest due to its remarkable efficiency in bioconverting a wide range of organic substrates. Here, we investigated how different agri-food processing by-products influence both the gut microbial community and the performance of BSF larvae, and how the supplementation with probiotics could improve host growth and bioconversion. Larvae were reared on different organic substrates - brewer’s spent grains, okara, potato peels and potato selection waste - alongside a standard laboratory diet. While BSF larvae were able to complete development on all tested substrates, performance metrics varied depending on the diet with a reduced larval survival on potato peels and potato selection waste. Gut bacterial composition and abundance were assessed by 16S rRNA high-throughput sequencing and quantitative PCR (qPCR), respectively. Our results revealed that distinct gut bacterial communities were hosted by larvae reared on different substrates. Then, we decided to apply bacterial probiotics to BSF larvae reared on the two suboptimal diets to observe any beneficial effects. In few cases the supplementation with bacteria suggested a positive effect. All in all, the characterization of the gut microbiota of insects provides valuable insights into the complex dynamics of insect–microbe interactions and supports the development of probiotic-assisted insect farming strategies. This work was supported by PRIN 2022 Project InProFarm (Insect Probiotic-assisted Farming: a promising tool to enhance edible insect health and performances), grant number 2022L4NJMK, funded by the European Union - Next Generation EU.