Diamond weevils and opal longhorns: The evolution of photonic crystals in Phytophaga

In weevils and longhorn beetles, iridescence arises from three-dimensional photonic crystals. These self-assembling nanostructures take the form of triply periodic networks with diamond, gyroid, or cubic geometry. Structural data and newly available phylogenetic information indicate that— despite their widespread geographic and taxonomic distribution— photonic crystals have evolved only once in weevils, independently of the crystals found in Cerambycidae. Hollow setae with an unordered, spongey network in the lumen appear to be a necessary precursor to three-dimensional photonic crystals; we propose an evolutionary pathway by which this transformation has occurred.