Lashing architecture in a meshed cocoon of a lichen-feeding moth Cyana (Lithosiini: Erebidae)

A cocoon is a protective outer casing that supports metamorphosis of lepidopteran insects. While some lepidopteran species build cocoons solely from silk, others may incorporate other surrounding materials or recycled body parts into their cocoons. Despite extensive knowledge of cocoons from commercially valuable species, information from species that secrete a low amount of silk remains scant. The lichen-feeding moth (Cyana) is an example of a lepidopteran genus that constructs its meshed cocoon from its larval-stage setae. In this study, we uncovered the lashing silk architecture of Cyana sp. on the setal joints, which served as the cocoon's main adhesive material and was responsible for the pupa hammock-like structure. Cocoon design reconstruction and electron microscopy observations (SEM and TEM) were conducted to obtain detailed structural information of the lashing silk. Results showed that the lichen-feeding moth secreted the silk for lashing setae together and creating joints. Cross-sectional analysis demonstrated two distinctive fibroin sizes and moldable sericin as components of the silk produced by this lichen-feeding moth. We also elucidated the detailed mooring silk linkage that involved hook-shaped structures in the hammocking pupal body. This study elucidated the structural foundation for further behavioral and bio-inspired design analysis of silk from low-producing silk lepidopterans.