Micro‐ and nanostructures of iridescent wing scales in purple emperor butterflies (Lepidoptera: Apatura ilia and A. iris)

Abstract

Apatura ilia (Denis and Schiffermüller, 1775) and A. iris (Linnaeus, 1758) are fascinating butterflies found in the Palaearctic ecozone (excepting the north of Africa). The wings of these insects are covered with a great number of two types of scales positioned like roof tiles. Type I scales are on the surface, while type II scales are situated below them. The structural color of the type I scales is recognized only on the dorsal side of both the fore and hind wings of the males of the aforementioned species. Both types of scales are responsible for pigment color of the wings, but iridescence is observed only in the type I scales. The brilliant structural color is due to a multilayer structure. The features of the scales, their dimensions and fine structure were obtained using scanning electron microscopy. Cross sections of the scales were then analyzed by transmission electron microscopy. The scales of the "normal" and clytie forms of A. ilia have a different nanostructure, but are of the same type. A similar type of structure, but with a different morphology, was also noticed in A. iris. The scales of the analyzed species resemble the scales of tropical Morpho butterflies.

Brilliant iridescence of Morpho butterfly wing scales is due to both a thin film lower lamina and a multilayered upper lamina

“…Characteristically, transmission electron micrographs of the wing scales show a Christmas-tree-like structure (Lippert and Gentil 1959 ; Ghiradella 1984 ). Similar structures are encountered in other nymphalid subfamilies, for instance the Apaturinae (Ćurčić et al 2012 ), but also in other lepidopteran families as the Lycaenidae (Tilley and Eliot 2002 ); all butterfly wing scales with multilayered ridges are referred to as Morpho type (Ghiradella et al 1972 ; Tilley and Eliot 2002 ; Giraldo et al 2008 ).…”

Coloration principles of the Great purple emperor butterfly (Sasakia charonda)

“…The optical principles governing the coloration of S. charonda are generally recognizable in other nymphalid butterflies. Very similar coloration patterns are displayed by the related purple emperor butterflies Apatura ilia and A. iris [1,20,21]. The multilayered ridges creating the blue iridescence of the dorsal wings are similar to those causing the strikingly blue color of Morpho butterflies.…”

Ridge and crossrib height of butterfly wing scales is a toolbox for structural color diversity

“…Second, by revealing a general law between ridge height and color hue, our findings shed new light on a new causative mechanism of structurally colored ridges across nymphalids 30,32,33,34,35 , pierids 36,37 , and lycaenid butterflies 38 . In many of these species the ridges have a Christmastree-like, or Morpho type, structure 39,8 , whose prominent side lamella were thought to be the main color-generating features 8,40,30,41,31 .…”