Impact of Agro-Industrial By-Products on the Hemolymph and Gut Microbiota of the Yellow Mealworm Tenebrio molitor

Introduction: Recently, insect farming has emerged as a sustainable alternative for producing protein-rich food and feed, as well as for bioconverting agro-industrial byproducts. The rearing substrate not only influences insect’s performance but also plays a crucial role in shaping the insect-associated microbiota, which in turn affects the host's physiology and immune system. Particularly, the gut microbiota of Tenebrio molitor L. (Coleoptera: Tenebrionidae), one of the most extensively farmed insect species, has received little attention when raised on different agri-food by-products. As well as the hemolymph, a key mediator of nutritional and immunological homeostasis in insects, remain largely unexplored. Objective: Aim of this research is to investigate the impact of various agro-industrial byproducts on the microbial community associated with the hemolymph and gut of T. molitor. Method: The hemolymph and gut microbiota of larvae reared on different by-products, i.e., 50% wheat bran + 50% brewer’s spent grain or 50% wheat bran + 50% tomato peels, and a control diet of 100% wheat bran, were analysed using 16S rRNA high-throughput sequencing. Moreover, the bacterial community abundance was quantified through qPCR on 16S rRNA gene. Findings: Insects’ performance varied depending on the by-products, characterized by different nutrient profiles. DNA extraction protocols were successfully optimized from both hemolymph and gut samples. Microbiological analysis revealed that the larval hemolymph and gut microbiota varied depending on the agro-industrial by-products. Conclusion: Future studies will be focused to elucidate the dynamics of the hemolymph and gut microbiota, key elements to enhance insect health in mass rearing environment.