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Biomechanical components of the plant-insect herbivore arms race: A model test in leaf-cutter ants

Walthaus, Olivia1; Deegala, Dilanka1; Delattre, Raphael1; Labonte, David1

Research facility: Imperial College London
Published Jun 18, 2025 on Dryad. https://doi.org/10.5061/dryad.r2280gbqh

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Abstract

Insects and plants have been locked in an evolutionary arms race spanning 350 million years and whilst much work focuses on the chemical components of this ancient contest, mechanical aspects remain largely understudied. We test a simple biomechanical model that relates the force required to cut thin leaf-like tissues to their mechanical properties, and the geometry of the cutting tool. To remove confounding effects of tool shape across size, we utilise leaf-cutter ant mandibles as a model system, who are also both an economically and ecologically relevant pest species. We measured the force required to cut both natural and pseudoleaves across mandible sizes (mass) and wear states (using pristine vs worn mandibles) using a custom built setup based on a fibre optic force sensor. To quantify the geometry of the cutting edge we measured the mandible cutting edge radius and wedge angle using focused ion-beam milling (FIB) and scanning electron microscopy (SEM). The results substantially support the model, enabling quantitative predictions. Fracture toughness is identified as a key mechanical defence trait for plants, edge radius as the critical geometric property of the insect mandible, and wear consequently emerges as a key modulator of cutting-forces, elevating it up to 5-fold above a physical minimum.