Dietary carbohydrate, protein and lipid modulation shape growth, nutritional profile and antimicrobial peptide gene expression in edible yellow mealworm larvae

Insects are highly nutritious and efficient producers of antimicrobial peptides (AMPs), and they can convert low-value organic side streams into high-quality biomass. This study investigated the effects of rearing substrates on growth, nutritional composition and AMP gene expression in the yellow mealworm larvae, Tenebrio molitor (TM). Four diets based on low-cost agricultural and bakery by-products were formulated with varying protein: non-structural carbohydrate (P:C) ratios and lipid levels: D1 (1:3, 7.5%), D2 (1:3, 9.5%), D3 (1:2, 7.5%), and D4 (1:2, 9.5%), adjusting the inclusions of raw material. Four-week-old TM larvae were reared under control conditions (10 000 larvae/replicate, five replicates/diet) and fed on 2.6 kg of diet per replicate. Dietary P:C ratio and lipid level significantly affected the growth performance of TM larvae in a stage-dependent manner. While low lipid levels primarily influenced early growth, 1:2 P:C ratio had a greater impact during later development. Survival, protein yield, feed conversion and nutritional composition were also affected by dietary modulations. The highest expression levels for the genes encoding the AMPs Coleoptericin-1 (6.62-fold change) and Cecropin-2 (8.92-fold change) suggested that 1:2 P:C combined with higher lipid content (9.5%) significantly enhances the expression of key AMPs. These findings highlight the importance of optimising dietary nutrient balance to improve mealworm production and nutritional quality supported by insect production using low-cost by-products.