Unveiling the nonlinear optical response of Trictenotoma childreni longhorn beetle

Abstract

The wings of some insect species are known to fluoresce under illumination by ultraviolet light. Their fluorescence properties are however, not comprehensively documented. In this article, the optical properties of one specific insect, the Trictenotoma childreni yellow longhorn beetle, were investigated using both linear and nonlinear optical (NLO) methods, including one‐ and two‐photon fluorescence and second harmonic generation (SHG). These three distinct optical signals discovered in this beetle are attributed to the presence of fluorophores embedded within the scales covering their elytra. Experimental evidence collected in this study indicates that the fluorophores are non‐centrosymmetric, a fundamental requirement for SHG. This study is the first reported optical behavior of this type in insects. We described how NLO techniques can complement other more convenient approaches to achieve a more comprehensive understanding of insect scales and integument properties.

Revealing the Wonder of Natural Photonics by Nonlinear Optics

“…Similarly, the yellow and fluorescent elongated scales covering the elytra of the log-boring beetle Trictenotoma childreni were investigated by nonlinear optical methods, including OPEF, TPEF, and SHG microscopy and spectroscopy ( Figure 7 ) [ 70 ]. These scales appear similar to the ones of the longhorn beetles Celosterna pollinosa sulfurea and Phosphorus virescens ( Figure 5 ) [ 68 ].…”

“…They contain fluorophores that give rise to a yellow visual appearance upon UV illumination. These observations allowed one to highlight the non-centrosymmetric nature of the fluorophores embedded within these scales [ 70 ].…”

“…This phenomenon arises in biological organisms, the integuments of which contain so-called fluorophores [ 55 , 56 ]. Examples include birds [ 44 , 57 , 58 , 59 ], insects [ 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 ], arachnids [ 72 , 73 ], mammals [ 74 ], amphibians [ 75 , 76 ], reptiles [ 77 ], marine animals [ 78 , 79 ], and plants [ 80 , 81 ] ( Figure 2 ). These molecules emit longer-wavelength light (typically, visible photons) following the absorption of incident shorter-wavelength light (typically, UV, violet or blue photons).…”

“…The interaction between fluorescent light and photonic structures was also highlighted in the scales covering the elytra of longhorn beetles Celosterna pollinosa sulfurea and Phosphorus virescens [ 68 ]. These scales exhibit yellow and turquoise colours under visible and UV incident light, respectively, with an underlying basal brown membrane ( Figure 5 a–d), akin to the beetles Euchroea auripigmenta and Trictenotoma childreni [ 69 , 70 ]. Through scatterograms and detailed series of simulations, it was demonstrated that the scales play the role of waveguides for light emitted by the embedded fluorophores ( Figure 5 e,f).…”

Optical costs and benefits of disorder in biological photonic crystals

“…144 Other longhorn beetles, such as Celosterna pollinosa sulfurea, Phosphorus virescens and Trictenotoma childreni, also combine disordered structures with yellow and uorescent pigments in order to produce a range of yellow hues. 145,146 Positional disorder in periodic multilayer structures Signicant interest lies in understanding the prevalence and extent of structural disorder in highly adapted biological systems whose functions include the generation of colour appearances and the general control of colour and light ow. To this end, we undertook an analysis of such disorder, its effects and the optical costs and benets with which it is associated.…”