Identification and functional characterization of silk fibroin genes in leaf-folding behaviour, silk properties and development of the rice leaf folder, Cnaphalocrocis medinalis (lepidoptera: Pyralidae).

Background: Outbreaks of the rice leaf folder (Cnaphalocrocis medinalis) poses a significant threat to rice production. Silk-spinning creates an enclosed leaf roll that protects larvae from predators and insecticides, while serving as a feeding site and facilitating host transfer and leaf-folding. Disrupting this behaviour could enhance control strategies. The silk fibroin gene, essential for silk production, remains poorly understood in C. medinalis.

Result: We cloned a 644-bp fragment of the fibroin heavy chain (CmFib-H) gene and the full-length 1158-bp fibroin light chain (CmFib-L) gene in C. medinalis. Both genes showed high expression during the larval stage, particularly in the silk glands. Third-instar larvae injected with dsCmFib-H, dsCmFib-L, or both, displayed disrupted silk-spinning and leaf-folding behaviours 48 h postinjection, with significantly reduced primary fold length and binding numbers compared to the dsGFP control. Ultrastructural analysis revealed disorganized silk and reduced diameter in co-injected larvae, and mechanical testing indicated significantly decreased compressive and tensile strength of the silk. Additionally, injecting dsCmFib-H and dsCmFib-L into 5-instar larvae significantly reduced pupation rate, pupal weight and eclosion rate 48 h postinjection.

Conclusion: Our study elucidates the pivotal roles of silk fibroin genes in leaf-folding behaviour, silk properties and the developmental processes of C. medinalis. These findings advance understanding of the functional roles of these important genes in insects and lay the foundation for the development of novel control strategies focused on targeting silk fibroin genes in C. medinalis. © 2025 Society of Chemical Industry.