Antireflection in Green Lacewing Wings with Random Height Surface Protrusions

Abstract

Wings of insects exhibit many functions apart from flying. In particular, their antireflection function is important for insects to avoid detection by their enemies. This function can be applied to antireflection biomimetic films in engineering fields. For such applications, confirming the antireflection mechanisms of insect wings is important. Herein, we used electron microscopy to compare the surfaces of green lacewing wings with and without a surface wax structure and recorded the transmittance spectra to clarify the surface structural and optical properties of insect wings. The spectral transmittance was higher for wings with a surface wax structure than for wings without a wax layer in the light wavelength regime from 500 to 750 nm. We constructed a concise model of the green lacewing wing with flake-like surface structure with a graded effective refractive index corresponding to the wing samples with a surface wax layer; we also constructed a simple thin-film model corresponding to the wing samples without a wax layer. The graded refractive indices were calculated using the effective medium theory, and the transmittance spectra of such models were then calculated using the transfer-matrix method. It was observed that the calculated spectra are in good agreement with the experimental results. In addition, wing samples without a surface structure induce thin-film interference. These results suggest that a wax structure can reduce the reflectance and increase the transmittance enabling the green lacewings to avoid detection by their enemies. These findings may lead to further advances in both the biomimetic field and fundamental research fields.

Mapping of Supramolecular Chirality in Insect Wings by Microscopic Vibrational Circular Dichroism Spectroscopy: Heterogeneity in Protein Distribution

“…Insect wings are interesting and attractive models for bioinspired and biomimetic materials because of their multifunctional characteristics, such as flying motion, antireflection, antihydrogenic, and photonic properties. − One fundamental problem is to unravel how these functions are realized in relation to the hierarchical organization of the component biomaterials. To investigate the nano- and microscale structures of insect wings, a number of spectroscopic and morphological methods have been applied, such as scanning electron microscopy (SEM), Fourier transform infrared (FTIR) microspectroscopy, solid-state NMR spectroscopy, synchrotron IR spectroscopy, and two-dimensional IR microscopy. − For example, dragonfly wing structures were systematically investigated by FTIR microscopy analysis . The main components, such as lipids and proteins, were identified from the peaks assigned to the CO stretching of ester (lipid) and amide I (protein).…”

Analysis of Surface Patterns and Electric Field Simulation of Antireflective Green Lacewing Wings

“…The observation method was also shown in a previous report . We observed the surface structure of wings using a field emission scanning electron microscope (FE-SEM) Ultra 55 (Zeiss, Oberkochen, Germany).…”

“…The preparation method of sample wings collected from green lacewings is also shown in a previous study . Green lacewings (Chrysopidae family) were captured on Thunberg’s meadowsweet (Spiraea thunbergii) and Japanese apricot (Prunus mume) trees at the Sagamihara Campus of Aoyama Gakuin University.…”

“…We obtained the relative permittivity of the base substrate as 2.43 using eq . The surface protrusions comprised various hydrocarbon molecules, such as fatty acids, and, hence, are complicated. We set the material of the surface protrusions as squalene, which is a major component of the surface protrusions, as shown in the Supporting Information of the previous report .…”

“…Previously, the optical properties of green lacewing wings have been investigated . Surface protrusions of green lacewing wings are flake-like, unlike those of cicada and glasswing butterfly .…”