The Ultrastructure of the Epicuticular Interference Reflectors of Tiger Beetles (cicindela)

Tiger beetles of the genus Cicindela exhibit iridescent structural coloration due to the presence of a non-ideal multilayer interference reflector located in the outermost 2 ̂ m of the integument. The reflector is composed of alternating layers of electron-lucent and electron-dense material. This series of layers was distinguished from chitinous procuticle by its position, ultrastructure and solubility in dilute KOH. The reflector appears homologous with the inner epicuticle of current models. Measurements of surface reflectance, refractive index and the dimensions of the alternating layers suggests that the dense layer has a refractive index (RI) near 2-0 and may be a melanoprotein.