Polarizing properties and structure of the cuticle of scarab beetles from theChrysinagenus

Abstract

The optical properties of several scarab beetles have been previously studied but few attempts have been made to compare beetles in the same genus. To determine whether there is any relation between specimens of the same genus, we have studied and classified seven species from the Chrysina genus. The polarization properties were analyzed with Mueller-matrix spectroscopic ellipsometry and the structural characteristics with optical microscopy and scanning electron microscopy. Most of the Chrysina beetles are green colored or have a metallic look (gold or silver). The results show that the green-colored beetles polarize reflected light mainly at off-specular angles. The gold-colored beetles polarize light left-handed near circular at specular reflection. The structure of the exoskeleton is a stack of layers that form a cusplike structure in the green beetles whereas the layers are parallel to the surface in the case of the gold-colored beetles. The beetle C. gloriosa is green with gold-colored stripes along the elytras and exhibits both types of effects. The results indicate that Chrysina beetles can be classified according to these two major polarization properties.

Graded pitch profile for the helicoidal broadband reflector and left-handed circularly polarizing cuticle of the scarab beetle Chrysina chrysargyrea

“…chrysargyrea for unpolarized incident light have been discussed before 26 but are here briefly recalled. Let us consider incident unpolarized light with Stokes vector [1, 0, 0, 0] T where T means transpose (see equation (8) in Materials and methods).…”

“…gloriosa 8–10,12,19 . More recently, this interesting topic has motivated several research groups around the world to perform intensive investigations 13–26 . Some of those studies on beetles of the Chrysina genus are based on SEM images and reflectance spectra of unpolarized incident light ( C .…”

Experimental degradation of helicoidal photonic nanostructures in scarab beetles (Coleoptera: Scarabaeidae): implications for the identification of circularly polarizing cuticle in the fossil record

“…These parameters are unlikely to relate to the preservation of Bouligand structures. The exocuticular laminae in green cuticle regions of the studied Chrysina show a distinctive cuspate arrangement (see [48]), but it is unclear how this physical structure could relate to preservation of Bouligand structures. Finally, experimental degradation does not alter the structure of the exocuticular laminae in any taxon studied.…”

Photonics in Nature: From Order to Disorder

“…Periodic multilayers have been reported in a number of species (Hunt et al, 2007;Del Río et al, 2016). They are extremely frequent in beetles (Coleoptera), in which this effect has long been known (see reviews: Land, 1972;Parker, 1998).…”