Dissertação de Mestrado #549: Wescley Valeriano

In dragonflies color has many functions the most important being sex recognition, courtship and territory behaviors. In Chalcopteryx rutilans those functions are performed by displaying their strongly iridescent hind wings. The aim of this work is to study the structures responsible for the male wing iridescence in Chalcopteryx. Visible range reflectance was measured for each different colored regions of the wings. In order to determine the internal microstructure of the region that exhibits the same color, Scanning Electron Microscopy (SEM) was performed in cross-sections of the wings. Transmission Electron Microscopy (TEM) images were obtained from ultrathin sections of osmium treated, resin embedded and uranyl-stained wing samples. The SEM and TEM images revealed that the wings have a multilayered structure alternating different electron density materials. The number and thicknesses of the layers change across the wing, correlating with the local color. The composition of! the layers is considered as being of chitin with different levels of melanin pigmentation. The electron density of the SEM cross-section images was assumed as being directly proportional to the optical density, and was used to define the modulation of the refractive indexes in the multilayered structure. The optical reflectance resulting from a structure with such a modulated refractive index was calculated numerically, using a guided mode expansion method. A good correlation is obtained between experiment and simulation.