Rearing of bioconverting insects for the valorization of by-products into valuable substances

Black Soldier Fly (BSF; Hermetia illucens, Diptera: Stratiomyidae) has emerged as a key species for the bioconversion of organic substrates within circular economy frameworks, offering sustainable solutions for food, feed, agriculture, and biomaterial production. Beyond insect biomass, BSF rearing generates valuable co-products, particularly larval frass, which can be exploited as an organic fertilizer and biostimulant, and protein-rich fractions that can be valorized for bio-based materials. Despite increasing interest, a comprehensive understanding of how rearing substrates, processing strategies, and application conditions influence the functional performance of BSF-derived products remains incomplete. This doctoral thesis integrates a critical review of the current state of insect bioconversion with experimental investigations aimed at evaluating the agronomic and biotechnological potential of BSF-derived products. The first part of the thesis provides an overview of insect bioconversion within food and feed systems, with particular emphasis on H. illucens, addressing regulatory aspects, life cycle assessment, and the role of automation in scaling sustainable insect farming. The influence of larval rearing substrates on BSF performance, nutritional composition, and microbiological aspects is then examined, highlighting substrate-driven variability as a central factor shaping downstream product quality. The experimental section focuses primarily on BSF frass and its multifunctional applications in agriculture. Frass extracts were evaluated as seed treatments in durum wheat (Triticum durum Desf.), assessing their effects on agronomic traits, antioxidant responses, and suppression of damping-off caused by Fusarium sporotrichioides. The presence of bioactive microorganisms was further investigated, leading to the isolation and characterization of plant growth-promoting bacteria (PGPB) from BSF frass. A large panel of isolates was screened in vitro for key plant growth-promoting traits, including phosphate solubilization, ammonia production, and phytohormone synthesis, and selected strains were tested in vivo on Arabidopsis thaliana, revealing differential effects on germination and early root development linked to substrate-dependent microbial abundance. In parallel, the agronomic suitability and potential phytotoxicity of BSF frass were assessed in lettuce (Lactuca sativa), identifying dose-dependent responses on germination, growth, and functional quality traits such as phenolic content and antioxidant capacity. These results underline the importance of optimizing application rates and processing conditions to maximize benefits while minimizing inhibitory effects. Finally, the thesis explores an alternative valorization pathway for BSF biomass, by investigating the production and characterization of protein-based bioplastic films derived from BSF larvae. Lipid removal, protein extraction, film formulation, and physicochemical characterization were conducted, followed by a preliminary evaluation of the films as biodegradable mulching materials, focusing on soil water evaporation control and macroscopic degradation behavior. Overall, this work positions BSF bioconversion as a versatile and tunable platform, demonstrating how substrate selection, processing strategies, and application context critically determine the agronomic and biotechnological performance of BSF-derived products, thereby contributing practical insights for their sustainable integration into circular bioeconomy systems.