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Calling in the pollinators


Flowering plants use both visual and chemical signals to enlist the help of insects for reproduction. Early flowering plants developed around 225 million years ago. Their flowers were of open construction to allow flies and beetles to visit them, and only provided simple sugars as rewards.
Seventy million years ago, long tubular flowers evolved that could only be pollinated by specific long-tongued moths and butterflies. Bees appeared 40 million years ago, also feeding from tubular flowers. The nectar of tubular flowers has complex sugars, fats and amino acids to stimulate egg production in these specialist pollinators.
An insects visual spectrum extends from yellow through to ultra-violet, whereas birds and mammals see from red through to violet. Red flowers are uninteresting to most insects. An insects appreciation of colour intensity is also different, with yellows, blues and ultra-violets being the most attractive. Flowers that attract day-time insects are the most brightly coloured, whereas colour is of little importance to night-time pollinators. Flowers frequently have colour guides such as stripes, spots and ultra-violet reflecting bands to guide the insect to the nectaries that lie beneath the pollen sacs.
Flowers use colour to attract insects from afar, but at close range the sense of smell enables precise species recognition. Flowers may also have odour guides leading the insect to the reward, such as an odour gradient or a difference in odour composition.
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