Butterfly wing colours: scale beads make white pierid wings brighter

Area of Science:

• * Entomology
• * Biophotonics
• * Evolutionary Biology

Background:

• * Butterfly wing coloration is crucial for species recognition, mate choice, and thermoregulation.
• * Wing scale morphology and nanostructure significantly impact light reflectance and perceived color.
• * Pierid butterflies (e.g., Pieris rapae, Delias nigrina) exhibit distinct white wing patterns, while Heliconius melpomene displays vibrant colors.

Purpose of the Study:

• * To compare the wing-scale morphologies of Pieris rapae, Delias nigrina, and Heliconius melpomene.
• * To correlate wing-scale structure with wing-reflectance spectra.
• * To investigate the functional significance of scale morphology in determining visual signaling.

Main Methods:

• * Comparative analysis of wing-scale microstructures using microscopy.
• * Measurement of wing-reflectance spectra across different butterfly species.
• * Correlation of structural features (e.g., scale beads) with optical properties.

Main Results:

• * Pieris rapae and Delias nigrina scales possess bead-like structures, absent in Heliconius melpomene scales.
• * The presence of beads on Pieris scales significantly increases white reflectance compared to H. melpomene.
• * Light scattering by scale beads enhances reflectance amplitude, contributing to a matt-white appearance.

Conclusions:

• * Scale microstructure, specifically the presence of beads, is a key determinant of white reflectance in pierid butterflies.
• * Enhanced reflectance improves visual discrimination between conspecific males and females, likely aiding in mate recognition.
• * The findings highlight the role of structural coloration in butterfly visual ecology and sexual selection.