Beetle Forewing Research Articles

Functional value of elytra under various stresses in the red flour beetle, Tribolium castaneum.

Coleoptera (beetles) is a massively successful order of insects, distinguished by their evolutionarily modified forewings called elytra. These structures are often presumed to have been a major driving force for the successful radiation of this taxon, by providing beetles with protection against a variety of harsh environmental factors. However, few studies have directly demonstrated the functional significance of the elytra against diverse environmental challenges. Here, we sought to empirically test the function of the elytra using Tribolium castaneum (the red flour beetle) as a model. We tested four categories of stress on the beetles: physical damage to hindwings, predation, desiccation, and cold shock. We found that, in all categories, the presence of elytra conferred a significant advantage compared to those beetles with their elytra experimentally removed. This work provides compelling quantitative evidence supporting the importance of beetle forewings in tolerating a variety of environmental stresses, and gives insight into how the evolution of elytra have facilitated the remarkable success of beetle radiation.

Non-hollow-core Cybister trabeculae and compressive properties of two biomimetic models of beetle forewings

In 2006, the forewing trabeculae of Cybister tripunctatus Olivier (i.e., Cybister) beetles were reported to be hollow, and a biomimetic structural model (i.e., Song's model) was reported to exhibit better compressive mechanical properties than a solid-core trabecula-honeycomb model (i.e., Chen's model). To test these assertions, the current study first observed the trabecular microstructure of the Cybister beetle and confirmed that the trabeculae are solid. Second, the finite element method (FEM) was used to perform a contrast analysis of the compressive mechanical properties of Song's and Chen's biomimetic models. The results indicated that Chen's model exhibited better compressive mechanical properties. These findings, which are completely opposite of Song's findings, were obtained because the comparison models designed for use in Song's study were not comparable to that of Chen's model in terms of the core volumes. This study will benefit the development of beetle forewing biomimetic research.

Characteristics of the tensile mechanical properties of fresh and dry forewings of beetles

Based on a tensile experiment and observations by scanning electron microscopy (SEM), this study demonstrated the characteristics of the tensile mechanical properties of the fresh and dry forewings of two types of beetles. The results revealed obvious differences in the tensile fracture morphologies and characteristics of the tensile mechanical properties of fresh and dry forewings of Cybister tripunctatus Olivier and Allomyrina dichotoma. For fresh forewings of these two types of beetles, a viscous, flow-like, polymer matrix plastic deformation was observed on the fracture surfaces, with soft morphologies and many fibers being pulled out, whereas on the dry forewings, the tensile fracture surfaces were straightforward, and there were no features resembling those found on the fresh forewings. The fresh forewings exhibited a greater fracture strain than the dry forewings, which was caused by the relative slippage of hydroxyl inter-chain bonds due to the presence of water in the fibers and proteins in the fresh forewings. Our study is the first to demonstrate the phenomenon of sudden stress drops caused by the fracturing of the lower skin because the lower skin fractured before the forewings of A. dichotoma reached their ultimate tensile strength. We also investigated the reasons underlying this phenomenon. This research provides a much better understanding of the mechanical properties of beetle forewings and facilitates the correct selection of study objects for biomimetic materials and development of the corresponding applications.

Comparative developmental analysis of Drosophila and Tribolium reveals conserved and diverged roles of abrupt in insect wing evolution

Morphological innovation is a fundamental process in evolution, yet its molecular basis is still elusive. Acquisition of elytra, highly modified beetle forewings, is an important innovation that has driven the successful radiation of beetles. Our RNAi screening for candidate genes has identified abrupt (ab) as a potential key player in elytron evolution. In this study, we performed a series of RNA interference (RNAi) experiments in both Tribolium and Drosophila to understand the contributions of ab to the evolution of beetle elytra. We found that (i) ab is essential for proper wing vein patterning both in Tribolium and Drosophila, (ii) ab has gained a novel function in determining the unique elytron shape in the beetle lineage, (iii) unlike Hippo and Insulin, other shape determining pathways, the shape determining function of ab is specific to the elytron and not required in the hindwing, (iv) ab has a previously undescribed role in the Notch signal-associated wing formation processes, which appears to be conserved between beetles and flies. These data suggest that ab has gained a new function during elytron evolution in beetles without compromising the conserved wing-related functions. Gaining a new function without losing evolutionarily conserved functions may be a key theme in the evolution of morphologically novel structures.

Review of beetle forewing structures and their biomimetic applications in China: (I) On the structural colors and the vertical and horizontal cross-sectional structures.

This paper discusses the progress made in China in terms of the structural colors, microstructure and mechanical properties of the beetle forewing. 1) The forewing microstructures can be classified into six phases, the first three of which are characterized by sandwich, multilayer and fiber layer structures, respectively. The fracture behaviors resulting from these three phases suggest that different scale microstructures or coupled adjacent scale microstructures can determine the macroscopic mechanical behavior of the forewing. 2) The forewing colors are derived from three features: regulation of the structural parameters of the internal optical structures, i.e., a sculpted multilayer composite two-dimensional nanopillar structure grating system; scattering on the three-dimensional surface of the bowl-shaped structure; and reversible color changes due to changes in the physical microstructure of fluffs. Their formation mechanisms were clarified, and fibers with ecological biomimetic structural colors have been developed. 3) Beetles exhibit a lightweight sectional frame structure with a trabecular core structure. Both of the joints on the left and right are concave-convex butt-joint structures with burrs, which provide an efficient docking mechanism with high intensity. The forewing of dichotoma exhibits a non-equiangular layered structure, which results in anisotropy in its tensile strength. Finally, the authors propose potential new research directions for the next 20 years.

Review of beetle forewing structures and their biomimetic applications in China: (II) On the three-dimensional structure, modeling and imitation.

This paper reviews the research progress made in China regarding the microstructure of the forewing trabeculae, their anti-peeling and anti-collisional mechanical properties, the three-dimensional (3D) microstructures of the forewings, their modeling, and their mechanical properties. We focus on 1) the distribution of the trabeculae in two types of beetles with a six-fold difference in density, the structure of the trabeculae and a proposed 3D model with an integrated trabeculae-honeycomb structure; 2) finite element analyses and experimental results showing that the average anti-peeling strength in the presence of trabeculae can be as much as approximately three-fold greater than that in the absence of trabeculae; 3) the strengthening mechanisms of these structures and describe an optimized double thin-walled biomimetic structure that possesses excellent absorption and buffering properties; 4) the development of technologies to produce fully integrated honeycomb plates with short fibers as a reinforced composite material and the verification that these plates are strong and lightweight and exhibit good integrity. Finally, we note the shortcomings in China in this field of research and propose possible future research directions in the field of biomimetic functional materials.

Biomimetic Studies of the Beetle Forewing in China

This report reviews biomimetic studies performed in China on the beetle forewing, noting that Chinese scholars studying bionics have substantially advanced various branches of biomimetic research in beetles. The report also proposes the development of branches of bionic research and establishes the foundation for corresponding experiments and theories. Then, using theA. dichotomaforewing as a an example, the cross-sectional shape, orientation of the laminated fiber layers, structure of the trabeculae, and respective mechanical properties of the forewing, as well as their biological significance, are reviewed. 1) The forewing has a lightweight border frame structure and an optimal design of variable cross-sections suitable for different positions, which achieves the specific second moment of inertia required for flight. 2) Due to the non-equiangular, laminated structure of the forewing, there are two types of tensile fracture morphologies: fiber breakage and residual bridging. This study demonstrates the anisotropy and the effectiveness of the forewings tensile strength by analyzing the orientation direction of the fibers. 3) The trabecular structure can be used to efficiently improve the peel resistance of the laminated composites. Based on the above points, possible directions for future work are also indicated in this paper.

Integrated honeycomb technology motivated by the structure of beetle forewings

The authors' previously presented architecture of beetle forewings has become the source of motivation for developing an integrated honeycomb structure. In this paper, we briefly review this architecture, describe the characteristics of this proposed novel structure, and, show that the beetle forewing contains a fully integrated honeycomb plate rather than a traditional “honeycomb” structure. Herein, a basic geometrical model of the fiber orientation is also provided, and how to develop an integrated honeycomb technology is discussed. By assuming that each hexagonal space of the honeycomb is filled with a male tool and a continuous plate is built, we consider disassembling the plate into a limited number of basic male tools and a honeycomb plate. The male tools were made with paraffin wax, and basalt fiber meshes were laid inside the female tool. We injected a mixture of shredded basalt fiber and epoxy resin into the mold for making a prototype structure. After solidification at a low temperature followed by the removal of the male tools via heating, an integrated honeycomb plate with trabeculae inside the honeycomb was manufactured. We consider that the proposed manufacturing process, which does not need bonding, is a breakthrough and it is envisioned that it will introduce an alternative to the traditional assembly method of manufacturing honeycomb plates.

Development of Integrated Bionic Honeycomb Plates

This paper describes the processes of integrated bionic honeycomb plates: A beetle forewing has integrated honeycomb structure, which consists of trabecula-honeycomb and a frame. It is expected to lead to a molding method enabling the creation of an integrated trabecula-honeycomb structure; we have developed an integrated honeycomb plate.

Development of Integrated Bionic Honeycomb Plates

This paper describes the processes of integrated bionic honeycomb plates: A beetle forewing has integrated honeycomb structure, which consists of trabecula-honeycomb and a frame. It is expected to lead to a molding method enabling the creation of an integrated trabecula-honeycomb structure; we have developed an integrated honeycomb plate.

Integrated honeycomb structure of a beetle forewing and its imitation

On the basis of past studies on the structures of beetle forewings, we have devised an approach to construct honeycomb plates in the form of an integrated body. We solve the problems encountered in the manufacturing processes, such as edge sealing and molding processes. Beginning with the knowledge that the forewing of a beetle, Allomyrina dichotoma, has a completely integrated trabecular honeycomb structure and a natural edge sealing structure, we investigated the formed mechanism, functions and mechanical properties of the structure. Inspired by the structure of the forewing, in this paper, we propose an edge sealing technique. Our novel technique establishes manufacturing processes that achieve integrated honeycomb plates with edge sealing. Furthermore, optimization methods have been developed to eliminate the influence of processing holes, by integrating male molds, and to shorten the molding time, by choosing a fast-curing resin.

Developmental Evolution: How Beetles Evolved Their Shields

Beetle forewings are modified into hardened structures called elytra. A recent study indicates that the evolution of elytra involved co-opting genes for exoskeleton formation into the wing development gene network of beetles on at least three separate occasions.

Basic study of biomimetic composite materials in the forewings of beetles

Inspired by bio-structures in optimal materials design, the microstructures and bio-structure design techniques in the forewing of the Allomyrina dichotoma beetle were examined in order to improve upon engineering designs. From this study, the following results were obtained: The fiber volume fraction and the shape of the fiber cross-section in the forewing depend on the forewing's position, while the shape of the cross-section is square or circular when fiber content is high or low, respectively. Within the laminated layers of the forewing's chitin fibers, fibers cross-link to form a reticular structure, thus providing two-dimensional strength and cleverly avoiding the common weakness found in woven fibers due to the physical strain caused by fiber overlap and bend. Between the laminated layers, the beetle's forewing is three-dimensionally reinforced by trabecular structures. In this study, both biomimetics composite materials and their design techniques are discussed.

Optimal composite structures in the forewings of beetles

In order to develop optimal biomimetic composite structures, research was conducted on the structural characteristics of Allomyrina dichotoma beetle forewings, with these characteristics to be further expounded upon. From this research, the following results were obtained: (1) It is found that the males, in comparison to females have both lighter and thinner forewings with a lower tensile fracture force, with the biological reasons behind these differences to be discussed later in depth. (2) It was found that densely distributed chitin fibers are located around the void lamination in the endocuticle of the forewing. They were found to have a rectangular cross-section with maximum reinforcement of fiber volume fraction; likewise, there exist sparsely distributed ones on the exocuticle in the Epipleuron tip of the forewing. These are of a circular cross-section, with a protein matrix that provides strong reinforcement. (3) Macroscopically the chitin fibers appear to exist independently of each other. However, this research discovered that, microscopically, the fibers have a reticular structure and through this structure, provide two-dimensional reinforcement to the same lamination of fibers. In comparison to a cloth weaving, it has many advantages, such as being unbendable and lacking concentrated stress points by crossing between the fibers, because they are not weaving cross points with those fibers. Lastly, the schematic structural model of the reticular structures of the fibers was proposed.

Lightweight composite structures in the forewings of beetles

In order to develop lightweight biomimetics composite structures, research was done on the structural characteristics of the forewings of two beetles, Allomyrina dichotoma and Prosopocoilus inclinatus, with these characteristics to be further expounded upon. The structural models of both forewings and trabeculae were also established. As a result, (1) the beetle forewing is of a sandwich plate structure with the central void layer of trabeculae and this is one of typical lightweight composite structures. The forewing of A. dichotoma is of an economic design, while the forewing of P. inclinatus is of a more durable design; (2) the chitin fibers in trabeculae connect continuously in a curvular shape to the chitin fibers on the upper and lower laminations, and it is clear that this structure greatly increases resistance against peeling for laminated composite structures.

Failure Type of Trabecular Root and Its Model Analysis in a Beetle Fore-Wing.

The relationships between the load peaks in load-displacement curves and the failure type of trabecular root in an interlaminar peeling process of a beetle fore-wing of A. Dichotoma were investigated and the interlaminar reinforcement mechanism was analyzed by using FEM. The peeling model with trabecular structure was proposed and the geometrical parameters for the model were determined by in-situ microscope observation. It was shown that the proposed model could be used to predict failure type of the trabecular root and to make clear the interlaminar reinforcement of a fore-wing. It was also found that the load peaks in a peeling process were proportional to the diameter of a trabecula, and depended on the failure type of the trabecular root. The principal stress at the peeling tip was very converged without the trabecula, but could eased by trabecula structure. It was shown that the fracture type of the trabecular root could be predicted by FEM model analysis.

Interlaminar Reinforcement Mechanism in a Beetle Fore-Wing.

Interlaminar Reinforcement Mechanism in a Beetle Fore-Wing.

Interlaminar Reinforcement Mechanism in a Beetle Fore-Wing

An interlaminar peeling test was conducted for an A. dichotoma beetle fore-wing with the interlaminar reinforcement mechanism being investigated. The load-displacement curves indicated the presence of many load peaks with the number of load peaks being equal to the number of trabeculae found in the chitin fiber laminae. This result suggested that each trabecula fracture contributed to a single load peak, which then combined to provide the interlaminar strength. The increment of interlaminar strength due to the trabecular in the chitin fiber laminae was approximately 30 times in a local region and 3 times in a whole region larger compared to that of the chitin fiber laminae without trabeculae. The chitin fibers were found to be connected between the chitin fiber laminae with the trabeculae being curved and continuous, whilst the trabeculae bonded chitin fiber laminae were distributed in two dimensions within the chitin fiber lamina plane. Furthermore, a strong reinforcement mechanism in nature was clarified with a model for the reinforcement mechanism being proposed.