The forewing-hindwing coupling of a black cicada Cryptotympana atrata (Hemiptera: Cicadidae): Functional morphology...

The wing structures and flapping dynamics of insects are diverse, which have important bionic implications for aircraft design. The black cicada, Cryptotympana atrata, which is a morphologically 4-winged insect, while its fore- and hindwings are coupled during flight. The functional morphology and kinematics in insects with coupled forewings-hindwings are still unclear. Further, although such wing coupling is common in nature, its impact on aerodynamic forces generated by flapping wings remains to be explored. In this study, we examine the micromorphology of the coupling structures on both fore- and hindwings of C. atrata. We analyze the kinematics and aerodynamics as well as variations in angle between the fore- and hindwings of C. atrata during tethered flight. The results show that fore- and hindwings are coupled through a hinge mechanism involving the rolled margin on the forewing and groove on the hindwing during flight. C. atrata follows a slender 0-shaped trajectory, and the dragged long trajectory line in pronation and supination is aimed to maintain stability. Due to the hinged coupling structure, there are significant changes in coupling angles during flight which influence wing twist, camber, and bending, ultimately enhancing aerodynamic forces by creating curved surfaces. This comprehensive study enhances our understanding of wing-coupling mechanisms and their functional significance for insects while providing valuable insights for future design and development of bionic coupled wings for flapping micro aerial vehicle systems.