Analytical model of the selective cutting mechanism used by ovipositors of sawflies
Sawflies (Insecta: Symphyta) use their ovipositors to incise plant tissue and deposit eggs, a task that demands precise substrate discrimination while preserving both ovipositor and host. How a passive selective mechanical system such as the ovipositor can discriminate between substrates based on material properties without active sensing or control remained until now an open question. This article presents an analytical model of the selective cutting mechanism inspired by sawfly ovipositors. Substrate cutting is shown to depend on an ultimate stress threshold determined by the interaction between blade geometry and substrate properties. The model captures the transition between cutting and ejection as a competition between a failure and an ejection criterion. Morphological modifiers, including serrulae and banding patterns, are shown to influence the ultimate stress threshold and are strongly dependent on both substrate hardness and elastic modulus. The model explains key previously reported observations obtained from prior experimental work that used scaled up biomimetic blades. These findings suggest novel directions in the design of surgical tools required to cut heterogeneous tissues with minimal extraneous damage.