A mulberry-free artificial diet reveals the effects of mulberry on larval development and cocoon traits in Bombyx mori (Lepidoptera: Bombycidae)

The silkworm, Bombyx mori (Lepidoptera: Bombycidae), is an economically important insect that serves as the foundation of the sericulture industry. As an oligophagous insect, the silkworm feeds primarily on mulberry leaves, and this strict dietary dependence limits the expansion of sericulture. Although artificial diets have been developed, mulberry powder is still the essential component of the artificial diet. This study developed a mulberry‑free artificial diet and investigated the essential role of mulberry using a genetically adaptable silkworm strain. Feeding experiments with graded mulberry powder revealed that, although silkworms on the mulberry‑free diet could cocoon, their survival, body weight, cocoon weight, and silk‑gland development were significantly impaired, showing a clear dose‑dependent response. Surprisingly, trehalose supplementation further suppressed growth, and the best-performing mulberry leaf group had the lowest hemolymph trehalose, indicating optimal development requires efficient trehalose utilization, not accumulation. Transcriptomic analyses demonstrated that mulberry intake broadly upregulates pathways related to energy metabolism and protein synthesis, rather than activating a single pathway. Several previously uncharacterized genes responded specifically to mulberry. These findings elucidate the broad physiological impact of mulberry leaves and provide a foundation for designing practical mulberry-free diets and identifying key mulberry-derived compounds.