Growth Performance, Diet Digestibility, and Chemical Composition of Mealworm (Tenebrio molitor L.) Fed Agricultural By-Products

SIMPLE SUMMARY: Insects are valuable alternatives to traditional protein sources for animal feed. Certain species have demonstrated that they can efficiently convert low-nutrient materials into quality body mass, making these species a viable protein and fat source. This study explores the effect of three agricultural by-products (broccoli by-product, tigernut pulp, and grape pomace) on the performance, digestive use, and proximate composition of Tenebrio molitor larvae. The growth and composition of the larvae were influenced by the type of by-product used, with the most protein-rich by-product resulting in larger larval biomass. However, diets based solely on a single by-product may penalize larval productivity and diet digestibility. The amino acid profiles of the insects were similar in all larvae, regardless of the diet, suggesting that these by-products can be used for insect rearing, achieving a sustainable production system aligning with the circular economy approach adopted globally. ABSTRACT: Humanity’s growing demand for animal protein exceeds the capacity of traditional protein sources to support growing livestock production. Insects offer promising partial substitutes, converting low-nutritional quality materials into high-value biomass. Hence, the bioconversion ability of Tenebrio molitor larvae was assessed by using three types of agricultural by-products (broccoli by-product, tigernut pulp, and grape pomace) at different inclusion levels (0%, 25%, 50%, and 100%) in a carbohydrate-based diet. Ten diets were formulated to assess their impact on the growth, diet digestibility, and nutritional composition of the larvae. For each treatment, eight replicates were employed: five for the growth-performance-digestibility trial and three for the complementary test of uric acid determination. The growth was influenced by the type of diet administered. The broccoli by-product resulted in higher larvae weight and a better feed conversion ratio. However, diets based solely on a single by-product (100%) compromised the productivity and diet digestibility. The larvae changed their nutritional composition depending on the rearing substrate, although the amino acid profile remained consistent. In conclusion, the studied by-products have the potential for use in T. molitor rearing as part of the diet but not as the exclusive ingredients, indicating promising opportunities for using agricultural by-products in T. molitor rearing and production.