Disorder in I-WP TPMS-like photonic networks creates angle-independent colors in Sternotomis virescens longhorn beetles

Photonic nanostructures can vary in their degree of local order and their final optical appearance is often further tuned by pigments. Longhorn beetles display vivid colors and rely on varying degrees of (dis)order combined with pigments to create complex color patterns via colored scales that contain photonic crystals and adorn the insects’ bodies. Using light microscopy, FIB-SEM tomography and FDTD simulations, we here investigated the mechanisms underlying the angle-independent color patterns in Sternotomis virescens longhorn beetles. The non-iridescent green stripes and blue feet of Sternotomis virescens beetles are produced by amorphous photonic crystals with subunits resembling I-WP TPMS unit cells with a local bcc symmetry [1]. A model of distorted bcc unit cells captures the networks’ connectivity and highlights their congruence with I-WP TPMS networks. The studied photonic networks are classified in analogy to photonic amorphous diamond structures [2] as photonic amorphous I-WP (PAI-WP). This work illustrates the complex interplay of structural and pigmentary color in longhorn beetles and shows how angle-independence in optical response is achieved by the novel PAI-WP networks.

[1] Kobayashi, Y., Ohnuki, R., & Yoshioka, S. (2021). J. R. Soc. Interface, 18(184), 20210505.

[2] Edagawa, K., Kanoko, S., & Notomi, M. (2008). Phys. rev. lett., 100(1), 013901.