Habitual dietary change reduces the antibacterial status of <i>Bombyx mori</i> by inducing an intestinal stress response

Abstract Rearing silkworms on artificial diets (AD) is crucial for sustainable sericulture, but their oligophagous nature makes adapting to non-mulberry leaf (ML) diets challenging. To date, the issues of reduced resistance and diminished vitality in silkworms reared on AD remain unresolved, and there is a lack of comprehensive research on alterations in their intestinal immune responses. In response to this knowledge gap, this study systematically investigated the impact of AD on intestinal stress and antibacterial capacity in silkworms. Compared to ML-fed silkworms, those reared on an AD exhibited a significant reduction in the antibacterial capacity of hemolymph and digestive fluids. Furthermore, Toll/IMD immune pathway genes from intestinal cells and antimicrobial peptide genes from fat bodies and hemolymph displayed signs of baseline immune stress, yet elicited a weak immune response following infection. Mechanistically, silkworms reared on an AD experienced a decline in intestinal antioxidant capacity, accompanied by elevated levels of reactive oxygen species. Additionally, the secretory function of midgut epithelial cells was impaired, the pH of digestive juices was decreased, the peritrophic membranes were damaged, the density of longitudinal muscle fibers in the intestine was lower, and intestinal motility was compromised. In conclusion, the intestinal barrier and functionality of silkworms reared on an AD were compromised, leading to a reduction in antibacterial capacity. These impairments were associated with pre-existing oxidative and immune stress conditions in the intestinal tissue under baseline conditions. These findings offer a novel perspective for improving silkworm feed formulations and developing immune-enhancing agents, extending beyond considerations of nutrient absorption.