Thursday , May 26 2022

Moths striking out in an evolutionary arms race with sophisticated wing design


Composite image of the moth Antheraea pernyi (top) and the Graphium agamemnon butterfly (bottom) showing photographs on the left echo image and ultrasound (tomography) on the right. Note that moth wings have weaker echoes (acoustic image) than butterfly wings.
Marc Holderied and Thomas Neil

3D color 3D representation of a 0.21 mm x 0.28 mm wing fragment of the moth Lasiocampa quercus showing the structure, variety and arrangement of base scales (orange) and cover scales (blue and yellow).

Simon Reichel, Thomas Neil, Zhiyuan Shen and Marc Holderied

Ultra-thin, ultra-absorbent and highly designed moth wings, moth wings could hold the key for developing technological solutions to survive in a noisy world.

As revealed in a new study published today at PNAS [date tbc], researchers from Bristol University have discovered the exact construction of moth wings that has enabled the species to bypass its most troublesome predator in a 65 million-year-old evolutionary arms race.

Using a variety of analytical techniques, including aerial cross-sectional imaging, acoustic mechanics and refractometry, the team from Bristol’s School of Biological Sciences found that the very thin-scale layer on moth wings has evolved ultrasound-absorbing properties that provide stealth acoustic camouflage. against relocation bats.

What makes the team’s discovery even more remarkable is that they have identified the first naturally occurring acoustic metamaterial. Metamaterial traditionally describes artificial composite material that has been engineered to exhibit physical properties that are superior to those available in nature. Naturally occurring metamaterials are very rare and have not previously been described in the world of acoustics.

Earlier this year, behavioral acoustics and sensory ecology expert Dr Marc Holderied and his fellow researchers reported how deaf moths had evolved ultrasound absorption rates on their bodies that allowed them to absorb 85 percent of the sound energy come in that bats use to find them.

The need to survive meant that moths evolved a 1.5mm deep-scale protective barrier that acts as a permeable sound amplifier. Such a protective barrier would not work on the wings, however, where the increased thickness would hinder the moths’ ability to fly. The key feature of acoustic metamaterials is that they are much smaller than the wavelength of the sound they are operating on, allowing them to be much thinner than traditionally built sound amplifiers.

In this latest study, the Bristol team, led by first co-authors Dr Thomas Neil and Dr Zhiyuan Shen, reveal that moths have gone one step further, creating a resonant amplifier that is 100 times thinner than the wavelength of sound it is. absorb, enabling the insects to maintain their lightness while reducing the potential for bats to detect echoes of their wings in flight.

By examining the sophisticated cross-sectional images of sound captured using ultrasound tomography, the team discovered that moth wings have evolved to make a resonant amplifier that provides effective protection against relocating bats. The findings could significantly strengthen the efforts of material scientists, acousticians, and sonar engineers to design bio-inspired sound amplifiers with exceptional deep wavelength performance.

“Amazingly, moth’s wings evolved a way to make a resonant absorber absorb all bat frequencies, by adding another amazing feature – they assemble many of these individually tuned resonators into different frequencies, which together create broadband absorption through acting. as an acoustic metamaterial – the first known in nature, ”said lead researcher Dr Holderied. “Such broadband absorption in the ultrathin structures of moth wings is very difficult to achieve, and that is what makes it so remarkable.”

This goes well beyond the limits that can be reached with classic pseudo-amplifiers of the kind currently used to absorb sound in office environments that use large, dense materials.

Dr Holderied added: “The pledge is one of much thinner sound amplifiers for our homes and offices, we would come close to a much more versatile and acceptable sound absorber ‘wallpaper’ rather than bulky absorption panels.”

This latest study builds on the team’s earlier work on single-scale acoustics-mechanics, and demonstrates how more traditional sound absorption by scales on moth bodies with much thinner wing structures can be achieved to provide whole organism acoustic protection .

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