Role of Color Interference on the Insect's Cuticle Coloration

Interference colors result from the reflection of light from a series of neighboring interfaces that are separated by distances comparable with a quarter of the wavelength of light. . Interference colors are common in some adults of Lepidoptera insects. The integument layers producing interference are formed by modifications of the scales. Each of the blue scales of the Morpho rhetenor butterfly, for instance, consists of a flat basal plate carrying a large number of near-parallel vertically aligned ridges that run parallel with the length of the scale. Within each ridge are series of horizontal layers, separated by air spaces. Collectively, the horizontal layers in each adjacent ridge form a series of reflecting surfaces, which are spaced such that a blue color is produced by interference. Interference colors in other insects are produced by reflection at the interfaces of layers in the cuticle which differ in refractive index. The refractive indices of the alternating layers in the pupa of the danaid butterfly, Euploea mulciber, are 1.58 and 1.37. In jewel beetles, Chrysochroa fulgidissima Buprestidae and tiger beetles, Cicindela japonica (Cicindellidae), these layers are in the exocuticle, but in tortoise beetles (Cassidinae) and some butterfly pupae they are in the endocuticle. Interference is responsible for the iridescence of the membranous wings of many different insects, particularly Odonata.