Chitosan Modulates Time-dependent Lipid Profiles and Lipase Activity in Infected Silkworms

Abstract

Flacherie, a serious bacterial disease affecting Bombyx mori, poses a substantial threat to sericulture by disrupting larval lipid metabolism and reducing silk productivity. This study investigated the effects of Staphylococcus aureus and Bacillus thuringiensis infections on lipid content and lipase activity in silkworm haemolymph and the therapeutic potential of chitosan derived from silkworm pupae and exuviae in mitigating these effects. Chitosan was extracted via deproteinization, demineralization, deacetylation and purification, mirroring established protocols. In-vivo treatments involved mulberry leaves coated with chitosan at 3500-5000 ppm, commercial chitosan (1000 ppm), ampicillin (1000 ppm) and appropriate controls, administered at multiple time points post‑inoculation. Haemolymph samples were collected daily during the fifth instar to assess lipid levels and lipase activity. Results showed that early application of higher‑dose chitosan significantly increased haemolymph lipid content in infected larvae, suggesting enhanced metabolic stability. Early application of pupal chitosan at 5000 ppm elevated lipid content (34.6 mg/mL in S. aureus and 32.8 mg/mL in B. thuringiensis) compared with infected controls (27.4 and 26.1 mg/mL). Lipase activity peaked at 0.185 U/mL on day six before declining toward pupation. Cocoon weight also improved, reaching 1.64 g at 5000 ppm versus 1.44 g in untreated controls, closely approaching the antibiotic effect (1.77 g). These results demonstrate that timely, high-dose chitosan application stabilizes metabolism, enhances silk yield and serves as an eco-friendly alternative to antibiotics in sericulture.