'Rainbow' weevil potential key to new colour-generation mechanism

The stout weevil has distinctive rainbow-coloured spots on its body made up of nearly-circular scales arranged in concentric rings of different hues

A “rainbow” snout weevil from the Philippines could hold the key to a novel colour-generation mechanism, a team of researchers from Yale-NUS College and the University of Fribourg in Switzerland discovered. The weevil, Pachyrrhynchus congestus pavonius, has distinctive rainbow-coloured spots on its body made up of concentric rings of different hues. While many insects can produce one or two colours, the weevil has the ability to produce a spectrum of colours.

The study was led by Yale-NUS College Assistant Professor of Science (Life Science) Vinod Kumar Saranathan and Dr Bodo D Wilts from the Adolphe Merkle Institute at the University of Fribourg, with Asst Prof Saranathan examining the rainbow-coloured patterns on the weevil using high-energy X-rays, and Dr Wilts undertaking detailed scanning electron microscopy and optical modelling.

The ultimate aim of the research is to determine how the weevil self-assembles those structures, said Asst Prof Saranathan, who also holds positions in NUS Biological Sciences and the NUS Nanoscience and Nanotechnology Initiative.

“The ability to produce these structures, which are able to provide a high colour fidelity regardless of the angle you view it from, will have applications in any industry which deals with colour 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 colour distortion. We can even use them to make reflective cladding for optical fibres to minimise signal loss during transmission,” he elaborated.

The team discovered that the weevil’s wings are composed of a three-dimensional crystalline structure made of chitin — the main ingredient in insect exoskeletons. The vibrant rainbow colours on the weevil’s scales were shown to be regulated by two factors — the size of the crystal structure, as well as the volume of chitin in the structure. Larger scales have a larger crystalline structure and use a larger volume of chitin and reflect red light, while smaller scales with a smaller crystalline structure and a smaller volume of chitin reflect blue light.