Potential for identification of wild night-flying moths by remote infrared microscopy

Abstract

There are hundreds of thousands of moth species with crucial ecological roles that are often obscured by their nocturnal lifestyles. The pigmentation and appearance of moths are dominated by cryptic diffuse shades of brown. In this study, 82 specimens representing 26 moth species were analysed using infrared polarimetric hyperspectral imaging in the range of 0.95–2.5 µm. Contrary to previous studies, we demonstrate that since infrared light does not resolve the surface roughness, wings appear glossy and specular at longer wavelengths. Such properties provide unique reflectance spectra between species. The reflectance of the majority of our species could be explained by comprehensive models, and a complete parametrization of the spectral, polarimetric and angular optical properties was reduced to just 11 parameters with physical units. These parameters are complementary and, compared with the within-species variation, were significantly distinct between species. Counterintuitively to the aperture-limited resolution criterion, we could deduce microscopic features along the surface from their infrared properties. These features were confirmed by electron microscopy. Finally, we show how our findings could greatly enhance opportunities for remote identification of free-flying moth species, and we hypothesize that such flat specular wing targets could be expected to be sensed over considerable distances.

Remote Nanoscopy with Infrared Elastic Hyperspectral Lidar

“…To validate the thickness value and the precision, we analyzed the same wing ( Figure a) in detail in the laboratory by polarimetric hyperspectral imaging [ 36 ] (Figure 3b,c). A spectral fringe model [ 26 ] was applied to the individual pixels, and the thicknesses were estimated across the wing surface (Figure 3d).…”

“…However, species in this order can be classified in the shortwave infrared region according to the surface roughness of the microstructures on their wing scales. [ 36 ] The same instrument presented here also enables quantification of such scale microstructures and also the equivalent absorption path lengths of melanin [ 36 ] and liquid water [ 39 ] in the body. Resulting parameters from scale microstructures and equivalent absorption path lengths can also be determined quantitatively and reported in microns for inter‐comparability between studies.…”

Dual-Band Infrared Scheimpflug Lidar Reveals Insect Activity in a Tropical Cloud Forest

“…If the system was white calibrated against a target with flat spectral reflectance, the band ratio from the body signal would be converted into the equivalent absorption path length of pure melanin in micrometers. 31 For the wing signal, this is slightly more complicated since clear wings produce thin film fringes (Fig. 3d).…”

“…Figure 3c displays the band placement in relation to the typical melanization of insects. 31 Figure 3d displays the ability of the two bands to produce resonant backscatter depending on the wing thickness for typical insect wing thicknesses. 32,33 Entomological lidar is a noninvasive technique, meant to capture the natural behavior of insects in situ and in real time.…”

Feasibility of Insect Identification Based on Spectral Fringes Produced by Clear Wings

“…Morphological data of insects could improve the interpretation of oscillatory signals [37], whereas differences in nano-and micro-surface structures could improve specificity in multispectral systems [38]. Allometric relationships between insect size and the morphology of their wings are known for a range of species [39][40][41], and allometric relationships are typically hard to alter.…”