Abstract
The dorsal wings of male Sasakia charonda butterflies display a striking blue iridescent coloration, which is accentuated by white, orange-yellow and red spots, as well as by brown margins. The ventral wings also have a variegated, but more subdued, pattern. We investigated the optical basis of the various colors of intact wings as well as isolated wing scales by applying light and electron microscopy, imaging scatterometry and (micro)spectrophotometry. The prominent blue iridescence is due to scales with tightly packed, multilayered ridges that contain melanin pigment. The scales in the brown wing margins also contain melanin. Pigments extracted from the orange-yellow and red spots indicate the presence of 3-OH-kynurenine and ommochrome pigment. The scales in the white spots also have multilayered ridges but lack pigment. The lower lamina of the scales plays a so-far undervalued but often crucial role. Its thin-film properties color the majority of the ventral wing scales, which are unpigmented and have large windows. The lower lamina acting as a thin-film reflector generally contributes to the reflectance of the various scale types.
Highlights
Sasakia charonda, the national butterfly of Japan since 1957, is locally known as oh-murasaki, or the great purple emperor
The dorsal wings of the male display a striking, blue-purple central wing area, which is accentuated by a surrounding brown margin dotted with orange-yellow spots
Wing patterning and coloration The dorsal wings of male S. charonda display a contrasting pattern created by a dark brown margin and cream to orange-yellow spots that surround a UV/blue-reflecting central area, which contains bright white spots (Fig. 1a, b)
Summary
The national butterfly of Japan since 1957, is locally known as oh-murasaki, or the great purple emperor. The dorsal wings of the male display a striking, blue-purple central wing area, which is accentuated by a surrounding brown margin dotted with orange-yellow spots. The species is distinctly sexually dimorphic, as the dorsal wings of the (slightly larger) female lack the brilliant blue-purple iridescence of the male [3]. As holds universally for butterflies, the color pattern is created by a lattice of scales that covers the wings like tiles on a roof. The scale material, chitin, is structured into a thin, plate-like lower lamina and an elaborate upper lamina.
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