How The Rainbow Weevil Produces Its Colors

Researchers have discovered that the structure and volume of chitin in the exoskeleton of rainbow weevils allow the insects to produce a vast spectrum of colors.

AsianScientist (Sep. 24, 2018) – Researchers from Yale-National University of Singapore (NUS) College and the University of Fribourg in Switzerland have discovered a mechanism for color generation in nature which could be used in screen displays, paints and cosmetics. They published their findings in the journal Small.

Pachyrrhynchus congestus pavonius, or the rainbow weevil, is distinctive for the rainbow-colored spots on its thorax and elytra. These spots are made up of nearly circular scales arranged in concentric rings of different hues, ranging from blue in the center to red at the outside, just like a rainbow.

While many insects have the ability to produce one or two colors, it is rare that a single insect can produce such a vast spectrum of colors. Researchers are interested to figure out the mechanism behind the natural formation of these color-generating structures, as current technology is unable to synthesize structures of this size.

In this study, an international team of researchers led by Assistant Professor Vinodkumar Saranathan of Yale-NUS, Singapore, and Dr. Bodo Wilts at the University of Fribourg, Switzerland, examined the rainbow-colored patterns in the elytra (wing casings) of a snout weevil from the Philippines, P. c. pavonius, using high-energy X-rays.

They found that the weevil had scales composed of a three-dimensional crystalline structure made from chitin, the main ingredient in insect exoskeletons. They also reported that the vibrant rainbow colors on the scales are determined by two factors: the size of the crystal structure of each scale, as well as the volume of chitin used to make up the crystal structure.

Larger scales reflect red light, while smaller scales reflect blue light. According to Saranathan, who previously examined over 100 species of insects and spiders and catalogued their color-generating mechanisms, this ability to simultaneously control both size and volume factors to fine-tune the color produced has never before been shown in insects.

“It is different from the usual strategy employed by nature to produce various different hues on the same animal, where the chitin structures are of fixed size and volume, and different colours are generated by orienting the structure at different angles, which reflects different wavelengths of light,” Saranathan explained.

“The ability to produce these structures, which are able to provide a high color fidelity regardless of the angle you view it from, will have applications in any industry which deals with color production. We can use these structures in cosmetics and other pigmentations to ensure high-fidelity hues, or in digital displays in your phone or tablet which will allow you to view it from any angle and see the same true image without any color distortion. We can even use them to make reflective cladding for optical fibers to minimize signal loss during transmission,” he added.

The article can be found at: Wilts & Saranathan (2018) A Literal Elytral Rainbow: Tunable Structural Colors Using Single Diamond Biophotonic Crystals in Pachyrrhynchus congestus Weevils.


Source: National University of Singapore.
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