Functional morphology of Priacma Serrata head and mandible

Priacma Serrata

Priacma Serrata © T. Hörnschemeyer

Priacma Serrata (Reticulated beetle or Bleach beetle) belongs to Cupedidae, one of the oldest beetle families in existence. Priacma Serrata are between 10–22 mm long, densely covered in articulated scales which are light to dark gray to gray-brown. The underside is dark brown in most specimens examined. Male beetles are attracted to bleach, hence the common name bleach beetle.

X-ray microtomography

Although male Priacma Serrata are easily collected, available data on internal morphology and biology are restricted to very few representatives. The use of X-ray microtomography (XMT) presented itself as a valuable technique for the investigation of insect structures. An important advantages of XMT over other methods is the possibility of a nondestructive investigation of internal structures.

X-ray projection (Courtesy: T. Hörnschemeyer)

Ventral view of XMT data (Courtesy: T. Hörnschemeyer)

Dorsal view of XMT data (Courtesy: T. Hörnschemeyer)

The specimens for the X-ray tomography were transferred to 100% ethanol and dried in a Balzer CPD 030 Critical Point Dryer. The dry specimens were mounted with soft wax to the sample stage of the X-ray machine. All measurements and reconstructions were made with a Skyscan 1072 high-resolution Micro-CT system.

Mesh Generation in ScanIP and ⁺ScanFE

FE mesh in +ScanFE

Mesh of mandible

Rapid Prototype of head

356 2D slices from the XMT data were imported into ScanIP and a simple FloodFill algorithm applied to segment the head structure. The segmented beetle head is about 5 mm long and the mandible measures 1.2 x 2.8 mm.
The segmented structure was then meshed within ⁺ScanFE which took only 5 minutes on a standard PC. From within ⁺ScanFE, a volume mesh was exported to Abaqus for further analysis. In addition, a scaled up surface mesh (.stl) was exported to produce an RP model of the head and mandible.

FE Simulation in Abaqus

Simulation of mouth opening (more detailed image)

A mesh of the head and mandible consisting of 70,000 nodes and 250,000 elements (the mandible on its own has 30,000 nodes and 106,000 elements) was imported into Abaqus were material properties and loads were applied. The results show that the mandible is curved to distribute stress, and it acts as a scoop mechanism.

Special thanks to Dr Thomas Hörnschemeyer, University of Göttingen who provided MicroCT data of the beetle specimen.

References

Hörnschemeyer, T., Beutel, R.G., Pasop, F., 2002. Head Structures of Priacma serrata Leconte (Coleoptera, Archostemata) Inferred from X-ray Tomography. Journal of Morphology. Vol(252), 298-314.