Excavation mechanics of the elongated female rostrum of the acorn weevil Curculio glandium (Coleoptera; Curculionidae)

Abstract

Elongated rostra (snouts) are remarkable features of many female weevils. The female of Curculio glandium uses the snout to excavate channels in acorns to oviposit. Considering the slenderness of the rostrum, the excavation of channels in solid substrates without buckling is a challenging task from both engineering and biological points of view. Here we aimed to examine the roles of the material properties and morphology of the rostrum in its buckling resistance. We employed microscopy techniques, non-destructive material characterisation and finite element (FE) modelling to shed more light on the excavation mechanics of the rostrum. We found that sexual dimorphisms are present not only in the length but also in the material, particularly the elastic modulus, and morphological features, particularly the curvature and thickness of the cuticular layers. Our FE modelling showed that those factors play essential roles to maximise the buckling resistance and minimise the bending resistance of the female rostrum. Considering that during excavation, the rostrum needs to be straightened without buckling, the functionality of the rostrum is likely to be a compromise between the flexibility and stiffness.