The external and internal structures of Amphizoa davidi Lucas (Coleoptera, Amphizoidae), using X-ray phase contrast microtomography.

The Chinese endemic water beetle Amphizoa davidi Lucas, is a rare and endangered species belonging to the monotypic family Amphizoidae (Coleoptera: Adephaga). A study of the external and internal structures of A. davidi is here presented, by using X-ray phase contrast tomography and light microscopy. Morphological details and three dimensional (3D) structures of this species are provided: skeletons, muscles, reproductive organs of male and female, nervous system, alimentary canal and pygidial gland. The reproductive organs of females are compared in two different developmental phases (ages): before copulation without mature ovaries and after copulation with mature ovaries. Such detailed 3D tomographic study based on micro-CT technology may promote our understanding of the detailed morphology in Amphizoidae and Coleoptera in general.

3D configuration of mandibles and controlling muscles in rove beetles based on micro-CT technique.

X-ray micro-CT is a powerful tool to visualize without damage details of the inner structures of beetles, the largest order of insects with a hard external skeleton. This contribution shows the three-dimensional (3D) reconstruction of the head morphology of three rove beetle species (Insecta, Coleoptera, Staphylinidae)--Noddia sp., Creophilus maxillosus, and Hesperosoma sp.--using X-ray microtomography at a spatial resolution of 6 µm. The details of skeletal muscle fiber insertions are described, giving a comprehensive overview of mandible mobility and organization. With the support of 3D rendering, we discuss the relationship among the mandible forms, the development of the muscles controlling the movement, and the head morphology. The well-developed posterior part of the head capsule is always accompanied by a well-developed mandible, a large adductor muscle, and a large apodeme for the wide areas of the muscle fiber attachment. In Noddia sp., muscles connected to the posterolateral angle of the head capsule are mainly short muscles, whereas in Creophilus maxillosus, the latter are mainly long muscles, and in Hesperosoma sp. no mandible adductor muscle fibers are present on the posterolateral angle of the head capsule. These results offer new invaluable information regarding the biting functions of beetle mandibles and the trend of their morphological change during their long-term evolution.

3D visualization of the microstructure of Quedius beesoni Cameron using micro-CT.

The investigation of the internal morphology of insects is usually performed using classical microtomy yielding optical micrographs of stained thin sections. The achievement of high-quality cross sections for microtomy is time-consuming and the risk of damaging sections is unavoidable. Moreover, the approach is impractical, in particular when quick acquisition of 3D structural information is required. Recently, X-ray computed microtomography (micro-CT) with a high spatial resolution was considered as a potential tool for the morphological classification of insects. We used micro-CT to investigate Quedius beesoni Cameron at the cellular length scale. This method provides a new powerful and nondestructive approach to obtain 3D structural information on the biological organization of insects. The preliminary images presented in this contribution clearly reveal the endoskeleton and the muscles of the head and the thorax with a full 3D structure. We also reconstructed the 3D structure of the brain of Quedius beesoni Cameron, and this is the first reconstruction in Staphylinidae, which will be a great advancement for morphological and phylogenic research. We claim that both the spatial resolution and the contrast characteristic of micro-CT imaging may fulfill the requirements necessary for zoological insect morphology and phylogeny, in particular, when a classification of a rare and unique insect specimen is required.