Yellow mealworms (Tenebrio molitor) as an alternative animal feed source: A comprehensive characterization of nutritional values and the larval gut microbiome

The present study aimed to evaluate the potential of yellow mealworms (Tenebrio molitor) reared using local agricultural by-products as an alternative feed for monogastric and ruminant animals. The mealworms were raised on oat-based (OB) and wheat-based (WB) by-products, and their nutritional properties and in vitro digestibility were evaluated, simulating the digestive system of both monogastric and ruminant animals. Furthermore, the gut microbiome of mealworm larvae was studied. Crude fat and most minerals were higher in larvae fed WB than those fed OB (P < 0.05), reflecting the nutritional profiles of the substrates. Larvae and pupae generally shared a common nutritional profile: lower contents of crude fiber, crude protein, and total amino acids, and higher crude fat, total fatty acids, and gross energy levels compared to adults (P < 0.05). Total essential and non-essential amino acid contents in larvae and pupae were similar to those of a commercial soybean meal (SBM). The in vitro dry matter and protein digestibility of larvae and pupae were similar to SBM and significantly higher (30%) than the values for adults for both monogastrics and ruminants. Firmicutes and Proteobacteria were the most abundant gut microbial phyla in larvae, and the gut microbiome revealed remarkable plasticity in response to altered nutritional status, such as starvation. A new insight into the nutrition of mealworm's metamorphic stages fed on agricultural by-products and how feeding modulates the larval gut microbiome provides an innovative approach to exploit mealworms as a sustainable and alternative animal feed source in the future.