Asian ladybird folding and unfolding of hind wing: biomechanical properties of resilin in affecting the tensile strength of the folding area

The deployable hind wings of Coleoptera are a highly specialized motive system that can fold and unfold in a unique way. Resilin in the wing membrane of Asian ladybird beetle (Harmonia axyridis) hind wings plays an active role during folding and unfolding of the wing. This study investigates the tensile properties of the hind wing and the distribution of resilin through the hind wing in an adult H. axyridis (Coleoptera: Coccinellidae) and how the resilin in the membrane of the hind wing affects its mechanical characteristics. The cross sections of veins of the hind wing are investigated by inverted fluorescence microscopy. Based on those results, two three-dimensional finite element models of the hind wing with/without resilin are established. The displacements, when subjected to pressure on the ventral side, are analyzed when the membrane wings are filled with/without resilin. The resilin in the hind wing is effectively for changing the flight performance such as the condition of stress and deformation. The results in this paper reveal the multiple functions of the resilin in the hind wings and have important implications for the design of biomimetic deployable micro-air vehicles.