The bees even managed the feat when the “flowers” were made with a yellow pigment – a situation in which the blue halo is very tricky for humans to spot. The results show that the bees were able to learn which square to visit for a tasty treat even though the squares were rearranged after each drink, suggesting bees can see the optical effects generated by the surface textures – and can spot the blue halo even without the presence of an iridescent sheen. The researchers then let bumblebees lose on these “artificial flowers”, with each bee in turn presented with two types of black square, one of which was coupled with a sweet solution and the other with a bitter-tasting one. To explore the impact of the phenomenon, the team constructed a series of small squares with different coloured pigments and surface textures – while one type had a smooth surface, another had ridges that gave rise to an iridescent sheen, and a third type had ridges that produced a blue halo. The upshot is that all the flowers appeared to have a “blue halo” – an effect that can be seen by the human eye for flowers with dark pigments.įurther work using computer models revealed that the blue halo depends not on the specific architecture of the tiny ridges, but on their level of disorder – in other words the degree of variation in their heights or spacings. But the team stumbled upon an additional quirk: the ridges also scattered blue and ultraviolet light. Photograph: Edwige Moyroud/APĭespite these differences, all of the flowers were found to have a weak iridescent sheen. The researchers let bumblebees lose on ‘artificial flowers’. The results reveal that the architecture of the nanostructures differed from species to species, with some showing variations in the spacings of their ridges while others showed variations in their heights. For the 11 species for which fresh flowers were available, the team also looked at how they scatter and diffract light. To do so they examined the petals of 12 species from across the flowering plant family tree, ranging from golden bartonia ( Mentzelia lindleyi) to the dark tulip known as “Queen of the Night”, using a variety of microscopy techniques. Writing in the journal Nature, the team reveal how they sought to explore the effect further to see if it occurred in other species with similar big, flat petals. The discovery has its roots in previous work from Glover’s team which revealed that tiny ridges on the petals of certain plants could diffract, or bend, light, giving them an iridescent sheen. Computer models revealed the blue halo depends not on the architecture of the ridges, but on their level of disorder “The exciting thing is that it is a new optical trick – we didn’t know that flowers could use disorder to generate a specific colour, and that is quite clever,” said Professor Beverley Glover, co-author of the research from the University of Cambridge. While the effect is not always visible to humans, it can be spotted by bees – suggesting the optical effect might help to attract the pollinators.
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