Chirality in Rhomborhina Gigantea beetle

The exocuticle of Rhomborhina Gigantea was examined for its iridescent properties. The iridescence was explained using theory of optical reflectors. The structural color was found due to chirality in the exocuticle layers and is structurally similar to cholesteric liquid crystals. The structure of the exocuticle was determined using electron microscopy. The optical properties were determined through reflection and diffraction experiments, giving strong green coloration of the exocuticle. The reflection spectra showed contrasting trends in the overall reflected intensity with respect to angle of incidence in transverse electric and transverse magnetic polarizations suggesting the presence of chirality. The average index of refraction and the half-pitch were derived from the optimal Bragg condition using the optical data. The half-pitch determined from scanning electron microscopy images was similar to the calculated values in both linear polarizations. The average refractive indices determined from the results in both polarizations were compared to the reported value. The consistency of the results confirmed that the structure responsible for the iridescent beetle was bio-optical analogue to cholesteric liquid crystals.