Investigation of hindwing folding in ladybird beetles by artificial elytron transplantation and microcomputed tomography
Tuesday, 2017/06/06 | 08:22:49
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Kazuya Saito, Shuhei Nomura, Shuhei Yamamoto, Ryuma Niyama, and Yoji Okabe ENTOMOLOGY SignificanceHindwings in ladybird beetles successfully achieve compatibility between the deformability (instability) required for wing folding and strength property (stability) required for flying. This study demonstrates how ladybird beetles address these two conflicting requirements by an unprecedented technique using artificial wings. Our results, which clarify the detailed wing-folding process and reveal the supporting structures, provide indispensable initial knowledge for revealing this naturally evolved optimization system. Investigating the characteristics in the venations and crease patterns revealed in this study could provide an innovative designing method, enabling the integration of structural stability and deformability, and thus could have a considerable impact on engineering science. AbstractLadybird beetles are high-mobility insects and explore broad areas by switching between walking and flying. Their excellent wing transformation systems enabling this lifestyle are expected to provide large potential for engineering applications. However, the mechanism behind the folding of their hindwings remains unclear. The reason is that ladybird beetles close the elytra ahead of wing folding, preventing the observation of detailed processes occurring under the elytra. In the present study, artificial transparent elytra were transplanted on living ladybird beetles, thereby enabling us to observe the detailed wing-folding processes. The result revealed that in addition to the abdominal movements mentioned in previous studies, the edge and ventral surface of the elytra, as well as characteristic shaped veins, play important roles in wing folding. The structures of the wing frames enabling this folding process and detailed 3D shape of the hindwing were investigated using microcomputed tomography. The results showed that the tape spring-like elastic frame plays an important role in the wing transformation mechanism. Compared with other beetles, hindwings in ladybird beetles are characterized by two seemingly incompatible properties: (i) the wing rigidity with relatively thick veins and (ii) the compactness in stored shapes with complex crease patterns. The detailed wing-folding process revealed in this study is expected to facilitate understanding of the naturally optimized system in this excellent deployable structure.
See: http://www.pnas.org/content/114/22/5624.abstract.html?etoc PNAS May 30 2017; vol.114; no.22: 5624–5628
Fig. 1. Wing-folding process in a ladybird beetle. (A) Hindwing of C. septempunctata. The basal part of the wing is supported by thick two veins: the MCL and RML. (B) Main crease lines of hindwing folding. The crease lines can be classified into three types based on their functions. Red lines are the PTF and ATF, which fold the wing along the longitudinal direction. Blue lines emerge between the MCL and RML and fold the wing along the transverse direction. The movements of these two types of lines are connected by diamond-shaped crease patterns (green lines). Fine lines represent mountain folding lines, and dashed lines represent valley folding lines. The dashed-line square corresponds to the paper model of Fig. 3. (C–G) Schematic representations of the wing-folding process. (C) Elytra are closed ahead of the hindwings, and they are simultaneously aligned backward. (D) Held by the elytron, the wing is slightly folded in the transverse direction and a triangular crease pattern emerges between the MCL and RML. (E) PTF and ATF are first introduced by the inner curve of the elytron and the edge of the elytron with the abdomen (PTF′ and ATF′). (F) According to the wing retraction by abdominal movement, the ATF′ drifts toward the apex of the wing by abdominal push and the wing is gradually retracted. The position of the PTF′ is held by the edge of the elytron. Finally, two transverse folding lines are stabilized into the positions of the PTF and ATF as shown in B. (G) Explanation of the stored shape. The hindwings are folded into a Z-shape on the folding lines of the PTF and ATF, and the diamond-shaped crease pattern emerges in the center of the hindwing. |
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