Abstract: 【Aim】 Insect wings are very delicate and flexible. The morphology and function of veins and wing articulation has long aroused wide concern of scientists in many fields. Due to limitation of historical conditions, the studies of insect wings mainly focused on vein morphology. Even the small amount of wing articulation morphology studies mainly stayed on the analysis of two-dimensional data. Furthermore, there is no report on the internal structures of the sclerites of insect wing articulations. The aim of this study isto reconstruct the internal and external three-dimensional morphology of the sclerites of insect wing articulations. The entire morphological information of the very complicated three-dimensional structures will be gained which is impossible to be demonstrated using traditional research methods. Thus, the relationships between the insect wing morphology and function could be inferred. 【Methods】 Four scarab beetle species from four families of Scarabaeoidea were scanned using Micro CT. The three-dimensional morphology of sclerites of wing articulations including the 1st, 2nd and 3rd axillary plates and median plate was reconstructed and analyzed. 【Results】 The morphological complexity of sclerites of wing articulations was demonstrated with the rendering and virtual cut of the three-dimensional models. The uneven curvature changes of external surface and the overlap of some parts of sclerites were found. The former mainly includes the protrusion, groove, and bend of external surface. The latter mainly includes the contact of some parts forming a tubular structure and some structure is concealed. Furthermore, the double-layer structures of the sclerites of wing articulations were found. The external layer is highly dense and solid, while the internal is a sponge-like structure. The relative spatial positions of folded and unfolded states of the sclerites were displayed in a three-dimensional way. The morphology of wing articulations of four species was compared. 【Conclusion】 Insect wing articulations are complex in internal and external morphology. Double-layer structure and the sponge-like internal structure may be related to the morphological adaptation strategy on minimizing the weight, saving energy in the movement and maintaining a rigid structure at the same time. Such morphological adaptations may have bionics significance for materials science, aerodynamics and some other fields.

Key words: Scarabs, functional morphology, wing articulation, sclerite, micro CT, three-dimensional reconstruction