Comparative Effects of Artificial Diets and Mulberry Leaves on Growth Performance and Gut Microbiota in Silkworms ( Bombyx mori )

The silkworm (Bombyx mori L., Thai strain Nanglai) is an important lepidopteran insect whose physiology is influenced by diet. This study compared artificial diet and mulberry leaves in larval performance, digestive enzyme activity, and gut microbiota using 16S rRNA gene sequencing. Survival was reduced in artificial diet-fed larvae at all instars. Mulberry leaf-fed larvae-maintained survival (97.33%-94.33%), whereas artificial diet-fed larvae declined from 84.33% in the first instar to 56.67% in the fifth instar, with survival 31.0% and 37.7% lower during the fourth and fifth instars, respectively. Total larval duration was longer under artificial diet feeding (34.0 vs. 27.67 days), while body weight did not differ significantly. Amylase activity was higher in mulberry leaf-fed larvae (3rd: 1,293; 5th: 2,394 U/mL) than in artificial diet-fed larvae (931 and 603 U/mL). Protease activity was lower in artificial diet-fed larvae at the third instar (779 vs. 886 U/mL) but higher at the fifth instar (462 vs. 352 U/mL). Microbial analyses revealed diet- and stage-dependent differences. At the fifth instar, alpha diversity was higher in mulberry leaf-fed larvae, with greater Chao1 richness, Shannon diversity, and Pielou's evenness. Principal coordinate analysis (PCoA) explained 91.11% of variation and showed clustering by diet and stage. Artificial diet feeding enriched Lactiplantibacillus and Saccharopolyspora, whereas mulberry leaf feeding supported greater taxonomic complexity. These findings indicate that artificial diet reshapes gut microbiota and digestive physiology, which may be associated with the observed reduction in larval survival during late development.