Structural and compositional analysis of the ovipositor of the sawfly Rhogogaster scalaris and its functional implications

Sawflies (Symphyta: Hymenoptera) use specialized ovipositors to cut into soft plant tissues for egg deposition. These ovipositors employ a reciprocating sawing motion and exhibit intricate morphological and material adaptations that enable selective tissue cutting with minimal damage to surrounding structures and preservation of the mechanical integrity of the ovipositors. While wood-boring ovipositors have been widely researched in biomimetics, the structural and compositional basis of soft-tissue-cutting ovipositors remains largely unexplored. This study characterizes the hierarchical material organization of sawfly ovipositors in relation to a recently identified cutting mechanism. Using a combination of scanning electron microscopy (SEM), micro-computed tomography (μCT), confocal laser scanning microscopy (CLSM) and polarized light microscopy (PLM), we investigate the composition, microstructure, and density gradients of materials present in the ovipositor of Rhogogaster scalaris. Our results reveal multi-scale structural heterogeneity, including spatially resolved density gradients, chitin fibre-bundle arrangements, and protein composition variations suggestive of mechanical optimization. These findings suggest that cutting efficiency is supported primarily by hierarchical structure and compositional gradients, rather than requiring prominent metal-based hardening, although trace or localized metal enrichment remains to be assessed through quantitative elemental mapping. Preliminary dehydration observations support the functional significance of hydration in maintaining mechanical integrity. This study provides the first detailed compositional and structural analysis of soft-tissue-cutting ovipositors and offers a structural and compositional basis that may inform future bioinspired designs of cutting tools aiming to enhance tissue selectivity and structural preservation.