Bogong Moths Are Well Camouflaged by Effectively Decolourized Wing Scales

Doekele G Stavenga,Jesse R A Wallace,Eric J Warrant

doi:10.3389/fphys.2020.00095

Doekele G Stavenga, Jesse R A Wallace + Show 1 more

Open Access

https://doi.org/10.3389/fphys.2020.00095

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Abstract

Moth wings are densely covered by wing scales that are assumed to specifically function to camouflage nocturnally active species during day time. Generally, moth wing scales are built according to the basic lepidopteran Bauplan, where the upper lamina consists of an array of parallel ridges and the lower lamina is a thin plane. The lower lamina hence acts as a thin film reflector having distinct reflectance spectra that can make the owner colorful and thus conspicuous for predators. Most moth species therefore load the scales’ upper lamina with variable amounts of melanin so that dull, brownish color patterns result. We investigated whether scale pigmentation in this manner indeed provides moths with camouflage by comparing the reflectance spectra of the wings and scales of the Australian Bogong moth (Agrotis infusa) with those of objects in their natural environment. The similarity of the spectra underscores the effective camouflaging strategies of this moth species.

Highlights

Bogong moths (Agrotis infusa) are night-flying moths, well-known for their highly directional, biannual long-distance seasonal migrations to and from the Australian Alps (Common, 1954; Warrant et al, 2016), a feat which requires the Earth’s magnetic field and visual landmarks as navigational cues (Dreyer et al, 2018)
We further investigated the structural coloration by applying imaging scatterometry, using a narrow aperture illumination beam
The gradient of melanin expressed in the wing scales of the Bogong moth is very sensible, because the high melanin concentration in the distal, exposed part of the scales filters the reflections of the scales’ lower lamina, so that only the long-wavelength part of the lower lamina’s reflectance spectrum contributes to the total wing reflectance

Summary

Introduction

Bogong moths (Agrotis infusa) are night-flying moths, well-known for their highly directional, biannual long-distance seasonal migrations to and from the Australian Alps (Common, 1954; Warrant et al, 2016), a feat which requires the Earth’s magnetic field and visual landmarks as navigational cues (Dreyer et al, 2018). The adults aestivate over the summer in cool alpine caves in the mountains of southeast Australia, including the Brindabella Ranges of the Australian Capital Territory, the Snowy Mountains of New South Wales and the Bogong High Plains in Victoria. Following this period of aestivation, the same individuals that arrived in the mountains months earlier leave the caves and return to their breeding grounds (a journey of up to 1000 km) to mate, lay their eggs and die. The classical example of camouflage is the peppered moth (Biston betularia), which developed a darker wing scale color as trees became covered in industrial soot and via the forces of natural selection induced by

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