Scale granules and colours: Sexual dimorphism in Trichonis (Lepidoptera: Lycaenidae, Theclinae)

Abstract A large fraction of dorsal wing surface ground scales show an unusual granulated nature, composed of material apparently extruded from the scale lumen in male individuals of both Trichonis Hewitson, 1865 species in the tribe Eumaeini, a rare Guyanian–Amazonian genus. Only a few not-granulated male specimens are known, females are not granulated. The granulated scales are investigated by various microscopic (optical, scanning and transmission electron microscopy, focused ion beam lamella cutting) and spectroscopic (optical reflectance, energy-dispersive X-ray (EDS), Raman) techniques. The characteristic blue colour unique in the South American representatives of the tribe is documented and analysed. EDS spectra show that the granules contain additional calcium and oxygen as compared with the un-granulated regions of the same scale. Electron diffraction (inside the TEM) did not reveal any crystalline component in the granules. The granulated wing surfaces of the males exhibit a UV absorption band at 280 nm, characteristic for biogenic CaCO3; therefore, the material of the granules is tentatively identified as CaCO3. It is shown that the granules influence the optical properties of the dorsal wing surface resulting in a characteristic spectrum.