Jewel beetles, Buprestidae, modulate bright structural colours by multileveled optical engineering and surface...

Area of Science:

• * Biophysics
• * Materials Science
• * Entomology

Background:

• * Buprestidae (jewel beetles) exhibit striking coloration due to nanostructured chitin and melanin layers.
• * These layers function as optical multilayer reflectors, with their optical properties determined by refractive index profiles.
• * The beetle's surface topography further modulates light reflection, influencing perceived color and texture.

Purpose of the Study:

• * To investigate the relationship between refractive index profiles, multilayer structure, and reflectance spectra in various Buprestidae species.
• * To model the optical properties of jewel beetle elytra using a matrix transfer model.
• * To correlate elytral surface sculpting with observed reflection characteristics (specular vs. diffuse).

Main Methods:

• * Transmission electron microscopy (TEM) was used to obtain high-resolution images of elytral cross-sections.
• * Refractive index profiles were derived from TEM images for multiple buprestid species.
• * A matrix transfer model was employed to simulate reflectance spectra based on the derived profiles and compare them with experimental measurements.

Main Results:

• * The refractive index profiles of several buprestid species were successfully determined.
• * Simulated reflectance spectra closely matched measured spectra, validating the model.
• * Elytral surface morphology significantly impacts reflection: smooth surfaces yield specular reflection (glossy), while sculpted surfaces produce spatially broadened reflections (matte).

Conclusions:

• * The combination of multilayer nanostructures and surface topography dictates the optical appearance of jewel beetles.
• * The matrix transfer model accurately predicts reflectance spectra, providing a tool for understanding structural color in insects.
• * Chrysochroa gratiosa serves as an extreme example of how surface sculpting can lead to a matte appearance despite multilayer reflectors.