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Entomophily or insect pollination is a form of pollination whereby pollen of plants, especially but not only of , is distributed by . Flowers pollinated by insects typically advertise themselves with bright colours, sometimes with conspicuous patterns (honey guides) leading to rewards of pollen and nectar; they may also have an attractive scent which in some cases mimicry insect . Insect pollinators such as have adaptations for their role, such as lapping or sucking mouthparts to take in nectar, and in some species also pollen baskets on their hind legs. This required the coevolution of insects and flowering plants in the development of pollination behaviour by the insects and pollination mechanisms by the flowers, benefiting both groups. Both the size and the density of a population are known to affect pollination and subsequent reproductive performance.
Butterflies and moths have hairy bodies and long proboscis which can probe deep into tubular flowers. Butterflies mostly fly by day and are particularly attracted to pink, mauve and purple flowers. The flowers are often large and scented, and the stamens are so-positioned that pollen is deposited on the insects while they feed on the nectar. Moths are mostly nocturnal and are attracted by night-blooming plants. The flowers of these are often tubular, pale in colour and fragrant only at night. Sphingidae tend to visit larger flowers and hover as they feed; they transfer pollen by means of the proboscis. Other moths land on the usually smaller flowers, which may be aggregated into flowerheads. Their energetic needs are not so great as those of hawkmoths and they are offered smaller quantities of nectar.
Inflorescences pollinated by beetles tend to be flat with open corollas or small flowers clustered in a head with multiple, projecting anthers that shed pollen readily. The flowers are often green or pale-coloured, and heavily scented, often with fruity or spicy aromas, but sometimes with odours of decaying organic matter. Some, like the giant water lily, include traps designed to retain the beetles in contact with the reproductive parts for longer periods.
Unspecialised flies with short proboscides are found visiting primitive flowers with readily accessible nectar. More specialised flies like and Horse-fly can visit more advanced blooms, but their purpose is to nourish themselves, and any transfer of pollen from one flower to another happens haphazardly. The small size of many flies is often made up for by their abundance, however they are unreliable pollinators as they may bear incompatible pollen, and lack of suitable breeding habitats may limit their activities. Some Pterostylis orchids are pollinated by midges unique to each species. Due to mutual specialisation, pollinators are highly dependent on floral diversity. Therefore, losses in plant diversity, such as those carried on by increasing land use, may be linked to extinctions of pollinators. A decline, for whatever reason, to one side of this partnership can be catastrophic for the other.
Flowers pollinated by bees and wasps vary in shape, colour and size. Yellow or blue plants are often visited, and flowers may have ultra-violet nectar guides, that help the insect to find the nectary. Some flowers, like sage or pea, have lower lips that will only open when sufficiently heavy insects, such as bees, land on them. With the lip depressed, the anthers may bow down to deposit pollen on the insect's back. Other flowers, like tomato, may only liberate their pollen by buzz pollination, a technique in which a bumblebee will cling on to a flower while vibrating its flight muscles, and this dislodges the pollen. Because bees care for their brood, they need to collect more food than just to maintain themselves, and therefore are important pollinators.
Other bees are nectar thieves and bite their way through the corolla in order to raid the nectary, in the process bypassing the reproductive structures.
Ants are not well adapted to pollination but they have been shown to perform this function in Polygonum cascadense and in certain desert plants with small blossoms near the ground with little fragrance or visual attraction, small quantities of nectar and limited quantities of sticky pollen.
Figs in the genus Ficus have a mutualistic arrangement with certain tiny Agaonidae wasps. In the common fig, the inflorescence is a syconium, formed by an enlarged, fleshy, hollow receptacle with multiple ovaries on the inner surface. A female wasp enters through a narrow aperture, fertilizes these pistillate flowers, and lays its eggs in some ovaries, with galls being formed by the developing larvae. In due course, staminate flowers develop inside the syconium. Wingless male wasps hatch and mate with females in the galls before tunnelling their way out of the developing fruit. The winged females, now laden with pollen, follow, flying off to find other receptive syconia at the right stage of development. Most species of fig have their own unique Commensalism species of wasp.
Plant-insect pairings
Some plant species coevolution with a particular pollinator species, such as the Ophrys apifera. The species is almost exclusively self-pollination in its northern ranges, but is pollinated by the solitary bee Eucera in the Mediterranean area. The plant attracts these insects by producing a scent that mimics the scent of the female bee. In addition, the lip acts as a decoy, as the male bee confuses it with a female that is visiting a pink flower. Pollen transfer occurs during the ensuing pseudocopulation.
Etymology
The word is artificially derived from the Ancient Greek: εντομο-, entomo-Liddell, Henry George and Robert Scott (1980). 9780199102075, Oxford University Press. ISBN 9780199102075 "cut in pieces, segmented", hence "insect"; and , phile, "loved".
Taxonomic range
Wind pollination is the reproductive strategy adopted by the Poaceae, Cyperaceae, Juncaceae and catkin-bearing plants. Other flowering plants are mostly pollinated by insects (or birds or bats), which seems to be the primitive state, and some plants have secondarily developed wind pollination. Some plants that are wind pollinated have vestigial nectaries, and other plants like Calluna that are regularly pollinated by insects, produce clouds of pollen and some wind pollination is inevitable. The Plantago media is primarily wind pollinated, but is also visited by insects which pollinate it. In general, showy, colourful, fragrant flowers like Helianthus, Orchidaceae and Buddleja are insect pollinated. The only entomophilous plants that are not Angiosperms are the dung-mosses of the family Splachnaceae.
See also
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