BOTANY

POPPIES AND BEES
Why don't bees pollinate red flowers except poppies?

By CARLA DE AGOSTINI
 

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The history of evolution is a history of relationships between species, as well as between species and the environment. When we smell a flower, for example, we actually hear a message addressed to the insects, a call to warn them that there is nectar waiting for them in exchange for transporting pollen. And the same goes for the choice of colours. Flowers as we know them are relatively recent. Angiosperms, i.e. plants that have flowers and fruit from seed, appeared between 135 and 140 million years ago and were not so colourful to begin with: fossils suggest that they were simple, dull-looking structures without much pigment, pale yellow or green at most. Today, with the exception of ferns, conifers, cycads and mosses, the majority of plant communities belong to the Angiosperms. Slowly, with the appearance of flowers, we also see the emergence of today's bright colours, an increasingly sophisticated mechanism to encourage pollination not only by wind or water but also by attracting insects.

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Many flowers have thus evolved to adapt to the needs and abilities of bees. Bees are responsible for 80% of pollination, without which there would be no apples, blueberries, cherries, avocados, cucumbers, almonds, onions, grapefruits, oranges, pumpkins and more. And it is to attract bees that the bright colour of the petals has become an important adaptation variable. The poppy has developed some of the most fascinating and unexpected strategies because bees don't perceive the bright red colour visible to the human eye but are attracted to the ultraviolet.

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Humans perceive colour through the pigment of the object and the part of the light it reflects. In bees, on the other hand, the field of vision is a mosaic of cones that enable them to recognise a different range of colours, help the insect to stay balanced during flight and identify each flower around it precisely, even at high speeds. The red hue is not perceptible to the bee's eye, and research has shown that it only distinguishes four colours: yellow (orange, yellowish green), bluish green, blue and ultraviolet. Therefore, flowers that are bright red to our eyes, such as the red violet or Chinese carnations, are not fertilised by bees, but by daytime butterflies.

On the other hand, flowers such as heather, rhododendron, cyclamen or clover have a purple hue that bees perceive as a blue colour, or a white colour perceived as bluish green. The poppy, however, is one of the few red flowers that most attracts bees. This is because the pigmented cells in its petals are arranged in such a way as to create air-filled spaces where the light is dispersed, allowing UV rays to be reflected and the ultraviolet range to be perceived by the bee, which then settles on it and fertilises it.

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And it is from the Sicilian, and in part Sardinian, shovels that the prickly pear arrives and invades Eritrea, planted both by 19th century Italian missionaries and by migrants of the first Italian colonization. Here, the beles, the name in Eritrean, are not only the fruit but also the nickname jokingly given by peers from the Horn of Africa to second-generation Eritreans living in Italy, because they arrive with the same punctuality as the fruit: in the summer rainy season, and then leave again.Today, Opuntia ficus-indica is used for a wide variety of products, both for its high nutritional value, rich in minerals, especially calcium, phosphorus and vitamin C, and for its mucilage, the substance that allows the plant to have water reserves. Thanks to this, the prickly pear has become a major player in eco-sustainable innovations. For example, a Mexican professor of chemical engineering, Sandra Pascoe Ortiz, has patented a plastic and biodegradable material: by mixing prickly pear juice with glycerin, proteins and natural waxes, she has obtained a liquid which, after being laminated and dried, becomes a completely non-toxic, biodegradable and edible bioplastic. In Italy, too, alternative uses of prickly pears are proliferating. For example, a glue for fresco restoration work has been experimented with using mucilage, and a textile industry has obtained cruelty-free eco-leather from its waste. But that's not all, there are also sunglasses made from their fibers, furniture and sculptural lamps made from the waste from shovels that are entirely biodegradable at the end of their life!

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Photo ©CRISTINA ARCHINTO