Assessing the influence of agro-industrial by-products on the hemolymph and gut microbiota of Tenebrio molitor

Edible insects are considered a potential resource for addressing food security issues due to their sustainability, high nutritional content, and ability to convert agro-industrial by-products, aligning with a circular economy perspective. 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, remains largely unexplored. Therefore, this research aimed to investigate the impact of different agro-industrial by-products composed by wheat bran or wheat bran + tomato peels or wheat bran + brewer"s spent grain on the microbial communities within the hemolymph and gut microbiota of T. molitor larvae. The analysis was conducted using high throughput 16S rRNA gene sequencing, while the abundance of bacterial communities was measured through qPCR targeting the 16S rRNA gene. Moreover, several chemical and biochemical parameters of larval hemolymph, including pH, and sugars were evaluated. Results highlighted that insects" performance varied depending on the by-products, characterized by different nutrient profiles. Microbiological analysis revealed that the larval hemolymph and gut microbiota varied depending on the agro-industrial by-products. This research offers valuable insights into the characterization of the hemolymph and gut microbiome in T. molitor under different rearing conditions, helping to bridge the knowledge gap, particularly in hemolymph microbiome studies. The use of agro-industrial by-products could potentially provide a cost-effective substrate for larvae to feed on, promoting a circular economy by reducing waste. 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.