Head-capsule design and mandible control in beetle larvae: a three-dimensional approach

This work provides the morphological basis of mandible kinematics of beetle larvae with different types of head capsules, orientation of mouthparts, mandible design, and feeding behavior. Short descriptions are provided for the hypognathous head of Liocola marmorata (Scarabaeidae), the prognathous head of Cybister lateralimarginalis (Dytiscidae), and the hyperprognathous head of Hydrophilus piceus (Hydrophilidae). Using 3D measurements of a set of points selected on the head, 3D models of head capsules and mandible articulations were made for the larvae of these three species. Further calculations of the models showed differences in spatial positions of mandible axes and insertion points of mandible muscles. Functional consequences of these differences and evolutionary aspects of changes in head design and mandible articulations are discussed. It is suggested that the approach used in this study may be useful for further comparative studies of mandible mechanics of a broad variety of insect taxa.