Photonic structures improve radiative heat exchange of Rosalia alpina (Coleoptera: Cerambycidae)

Visible and near-infrared radiation may be transmitted or absorbed differently by beetle elytra according to habitat preference

“…Quite the contrary, the species with darker and thicker elytra ( O. medius ), which inhabited sunny areas, appears to be better able to absorb infrared and visible radiation. These results are in agreement with those of a recently published study on the thermal capacity of the elytra of the saproxylic beetle Rosalia alpina (Linnaeus, 1758) (Pavlović et al, 2018), which inhabits the sun-exposed forest along the Euro-Caucasian region. The black patches present in the elytra of this species are also able to absorb visible radiation to heat its body, but the elytra also serve to quickly transmit the infrared radiation to attain thermal equilibrium.…”

“…Our results agree with those of previous studies (Carrascal, Jiménez-Ruiz & Lobo, 2017; Amore et al, 2017; Alves, Hernández & Lobo, 2018) in that elytron reflectance is minimal, transmittance of infrared radiation is very high, and most of the ultraviolet and visible radiation is absorbed by the elytra. All these exoskeletal characteristics are consistent with the requirements of an ectothermic organism that spends a good deal of time in the soil and would need to obtain body heat from the surrounding infrared and visible radiation (Pavlović et al, 2018). Thus, elytra seem to be highly transparent to the heat coming from the sun or the environment but opaque to the most energetic wavelengths capable of causing harmful effects (Beresford, Selby & Moore, 2013).…”

“…On the other hand, and in agreement with previous results (Alves, Hernández & Lobo, 2018), elytral transparency to infrared radiation seems to be slightly higher on the inside part of the elytron than on the outside part, suggesting that the elytra can be slightly more effective at facilitating the removal of body heat in these dung beetle species. In a recent paper, Pavlović et al (2018) demonstrated that short (1,400–3,000 nm) and mid (3,000–8,000 nm) infrared wavelengths, which are mostly absorbed by atmospheric gasses (Eltbaakh et al, 2011), can be used to dissipate body heat. Further studies are needed to assess whether the transmittance of these infrared wavelengths is especially high from the internal side of the elytra.…”

“…In our case, the darkest elytra seem to make the access of infrared and visible radiations into the body more difficult, also facilitating the absorbance of these types of radiation; however, the elytra do not influence the management of UV radiation. As the transmittance and absorbance of solar radiation may vary between the elytral parts with different colors and structures (Pavlović et al, 2018), the future use of microspectrometry will be recommended to further assess the specific role of black patches in thermal balance.…”

“…Consequently, this temperature increase probably results from the transmittance and/or absorbance of non-infrared wavelengths by the dorsal cuticle. The elytra of these species could absorb most of the highly energetic radiation from the ultraviolet and visible parts of the spectrum and convert it into body heat (Alves, Hernández & Lobo, 2018; Pavlović et al, 2018). All these results suggest that the beetle exoskeleton may allow for the “passive thermoregulation” of body temperatures.…”