Characterization of silk-like materials from larval salivary glands of the dipteran, Keroplatus testaceus

Abstract Silk-like secretions are well-studied in many insects but remain poorly characterized in Diptera. Larvae of the dipteran Keroplatus testaceus produce two distinct silk-like materials—a mucus web and a cocoon—from their labial salivary glands, differing in composition and function. Here we combined histology, transcriptomics, electron microscopy, proteomics, mechanical testing, and FTIR spectroscopy to characterize these secretions. Neither contains fibroin; instead, both comprise hydrophilic proteins including collagen-like, mucin, and novel proline-rich proteins. Structural predictions and FTIR analyses reveal β-sheets, α-helices, and polyproline II helices, contributing to mechanical robustness despite high hydration. The mucus web facilitates larval mobility and spore capture, while the cocoon provides mechanical protection during pupation. These findings reveal a fibroin-independent silk system adapted to humid, microbe-rich environments, expanding understanding of insect silk diversity and offering insights into novel biomaterials.