The spectacular and peculiar structural color of Chrysochroa jewel beetles (Coleoptera: Buprestidae)

Beetles in Golden Skin: Structural Color in Chrysochroa jewel beetles (Coleoptera: Buprestidae)
Chrysochroa jewel beetles, in the family Buprestidae, are known for their spectacularly bright, saturated, and diverse coloration, which originates from the selective reflection of light by alternating chitin and melanin in the epicuticle. Despite Chrysochroa’s widespread popularity among beetle enthusiasts both amateur and professional, the optical properties and mechanisms of their structural color (and Buprestidae structural color in general) has only been investigated in a few select species. Consequently, while many of the most brilliantly colored species have been well represented in entomological arts and collections, the physical and evolutionary origins of their colors have remained unexplored by science. Twenty-eight select taxa representing all 13 Chrysochroa subgenera were investigated to provide an overview of the objective optical properties and underlying mechanisms of their diverse structural color. Optical properties of Chrysochroa structural color were quantified using spectrophotometry. Three major morphological adaptations through which Chrysochroa beetles modify color: cuticle surface sculpture, epicuticle chitin-melanin multilayer organization, and refractive index modification within each layer, were investigated and characterized using Transmission (TEM) and Scanning (SEM) Electron Microscopy, as well as computational modeling via MATLAB. Several previously unknown architectures of multilayer organizations with unique optical properties were discovered. Surface sculpture morphology, an often over overlooked trait in color production, was shown to play a key role in the production of "super-black" and other unique visual effects by controlling the directional reflection of light.