Variation in the circularly polarized light reflection ofLomaptera(Scarabaeidae) beetles

Abstract

An extended spectroscopic study on the left-through-left circularly polarized reflection spectra of a large number of beetles from the Australasian Scrabaeidae:Cetoniinae of the Lomaptera genus was undertaken. We have obtained a five-category spectral classification. The principal spectral features, which even within the genus range from blue to infrared, are related to structural chirality in the beetle shells. The detailed features of each spectral classification are related to different structural perturbations of the helix, including various pitch values and abrupt twist defects. These spectral characteristics and associated shell structures are confirmed on the basis of simple modelling. An important conclusion from our study is that the simple helical structure resulting in a single symmetric Bragg peak is not the dominant spectral type. Rather the reality is a rich tapestry of spectral types. One intriguing specimen is identified via a scanning electron micrograph to consist of a double interstitial helix leading to a particular double-peak spectrum.

Circularly polarized reflection from the scarab beetleChalcothea smaragdina: light scattering by a dual photonic structure

“…Beyond confirming the reflection of LCP light in two of the investigated specimens, the authors offered no additional insight into the CP behaviour exhibited by the beetles. The observation of CP reflected light for species belonging to the Lomaptera genus has been reported elsewhere, first by Neville & Caveney [37], and, more recently, by Carter et al [86], although, neither makes reference to the beetles' surface topography. Xu et al [85] presented a simplified model for the origin of the reflectance of the exocuticle structures revealed via TEM cross-sections, in which traditional multilayer reflectors, formed from alternating layers comprising distinct materials of high and low refractive index, were assumed.…”

Structural colours in the frond of Microsorum thailandicum

“…To obtain more information on the arrangement of the cellulose stack, we furthermore tried to use the classifications proposed by Carter et al for a non-ideal helicoidal reflector in beetles. The best matching classification is 'Spectra with diminishing oscillations', but such spectra are not well described by a few local defects or rsfs.royalsocietypublishing.org Interface Focus 9: 20180055 pitch changes, as described in their supplementary information [39]. Furthermore, looking at individual spectra from several cells (figure 5f ), we also found that no single classification fitted them all.…”

“…The model adopted so far to systematically analyse the optical response by helicoidal structures does not encompass all factors contributing to the spectral response. By trying to fit our spectra to the model developed to take into account defects and irregularities in spectra of helicoidal beetle cuticles [39], we were not able to reproduce all the measured spectral features. Therefore, we conclude that a few discrete defect sites do not dominate the reflection spectrum of the plant cell walls.…”

Catalogue of the types of the Scarabaeidae in the National Museum of Natural History of Luxembourg (Coleoptera)

“…Rigout and Allard (1997 : 88) treated L. d. viridipes as a variety of Lomaptera helleriana Valck Lucassen, 1961 without explanation. However, De Jong (1970 : 266) and Carter et al (2016 : 6) treated it as Lomaptera viridipes Moser, 1908.…”