Entomophily
Entomophily or insect pollination is a form of pollination whereby pollen of plants, especially but not only of flowering plants, is distributed by insects. 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 mimics insect pheromones. Insect pollinators such as bees 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.[1]
Coevolution
History
The early
The plant's needs
Wind and water pollination require the production of vast quantities of pollen because of the chancy nature of its deposition. If they are not to be reliant on the wind or water (for aquatic species), plants need pollinators to move their pollen grains from one plant to another. They particularly need pollinators to consistently choose flowers of the same species, so they have evolved different lures to encourage specific pollinators to maintain fidelity to the same species. The attractions offered are mainly nectar, pollen, fragrances and oils. The ideal pollinating insect is hairy (so that pollen adheres to it), and spends time exploring the flower so that it comes into contact with the reproductive structures.[11]
Mechanisms
Many insects are pollinators, particularly bees, Lepidoptera (butterflies and moths), wasps, flies, ants and beetles.[11] On the other hand, some plants are generalists, being pollinated by insects in several orders.[12] Entomophilous plant species have frequently evolved mechanisms to make themselves more appealing to insects, e.g., brightly coloured or scented flowers, nectar, or appealing shapes and patterns. Pollen grains of entomophilous plants are generally larger than the fine pollens of anemophilous (wind-pollinated) plants, which has to be produced in much larger quantities because such a high proportion is wasted. This is energetically costly, but in contrast, entomophilous plants have to bear the energetic costs of producing nectar.[13]
Butterflies and moths have hairy bodies and long proboscides 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. Hawkmoths 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.[14]
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.[11] 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.[15]
Unspecialised flies with short proboscides are found visiting primitive flowers with readily accessible nectar. More specialised flies like
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.[17] 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.[11]
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.[17]
Plant-insect pairings
Some plant species
Figs in the genus
Etymology
The word is artificially derived from the Greek: εντομο-, entomo-[20] "cut in pieces, segmented", hence "insect"; and φίλη, phile, "loved".
Taxonomic range
Wind pollination is the reproductive strategy adopted by the
See also
References
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- ^ a b c d Kimsey, L. "Pollinators We Never Talk About". University of California, Davis: College of Agricultural and Environmental Sciences. Archived from the original on 10 April 2016. Retrieved 25 March 2016.
- ^ Köhler, Andreas; Sühs, Rafael Barbizan; Somavilla, Alexandre (2010-11-11). "Entomofauna associated to the floration of Schinus terebinthifolius Raddi (Anacardiaceae) in the Rio Grande do Sul State, Brazil = Entomofauna associada à floração de Schinus terebinthifolius Raddi (Anacardiaceae) no Estado do Rio Grande do Sul, Brasil | Somavilla |". Bioscience Journal. 26 (6). Retrieved 18 April 2014.
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