People may view insects with distaste but these tiny creatures perform important functions for humankind. Perhaps the most useful of these is to facilitate pollination of plants, thereby providing us with much of our food. This vital work goes on silently and we take it for granted. We would be well advised to pay more attention, however, as the well-being of insects is under threat.
Pollination in plants is the process whereby pollen, bearing the male germ cell, is transferred from the male organ (stamen) to the female sex organ (pistil), leading to fertilisation and the formation of a seed or fruit.
Sex is just as important for plants as for animals for generating genetic variation. But plants cannot move about to find mates. Some plants overcome this problem by fertilising themselves. They are hermaphrodites, i.e. their flowers contain male and female organs.
Most plants need help with pollination. Some species such as grasses simply rely on wind to move pollen about - a hit-and-miss mechanism. Some pollen gets to the pistil successfully but much is wasted by landing in inappropriate places - like the noses of hay-fever sufferers.
Plants have developed devices to induce animals to carry pollen from flower to flower. Pollen itself is a direct reward, high in protein (up to 30 per cent) and in fat (up to 10 per cent). Insects gather pollen for food and in the process are "dusted" with more pollen which is transported to other flowers as the insect forages.
The only function of plant nectar is reward for pollinators. It is primarily a dilute sugar solution, but contains variable amounts of amino acids, lipids and vitamins. Since nectar and pollen are not obvious to pollinators, plants have developed floral displays to attract them. Fragrances also attract passing pollinators.
Some flowers successfully trick insects into visiting them, e.g. orchids in the genus Ophrys, by looking and smelling like the female insect.
Males of many of these insects emerge before the females. The only "action" available is with orchid flowers with whom they enthusiastically copulate (pseudocopulation), picking up pollen dust in the process. They repeat the process with other flowers, depositing the pollen in just the right place.
Humans have recognised the importance of pollination for crop-raising for 3,500 years, but the importance of insects in cross-pollination was not recognised until the 19th century. Charles Darwin emphasised the importance of insects as pollinators.
He "explained" how the power of the British Empire was maintained by its spinsters: spinsters kept cats, which kept down the population of mice, which were then unable to destroy bumble bee nests, which then pollinated red clover, which then fed cattle, which were eaten by the soldiers who extended and defended the Empire.
There are 130,000 to 200,000 pollinating species worldwide. These include beetles, moths, butterflies and flies, and as many as 40,000 species of bee. Other animals disperse pollen indifferently or accidentally, but bees are devoted to the task.
Evolution has honed bees to fly exclusively on nectar fuel and to use only pollen as food for their broods. Bees have special structures on the hind legs for carrying pollen.
The commercial importance of pollinators is huge. About $10 billion worth of crops are pollinated by bees alone every year in America. These include plants whose fruits arise directly from the action of pollinators, such as apples, almonds, avocados, cherries, cranberries, citrus fruits, cucumbers, melons, peaches, pumpkins, strawberries, nectarines, kiwi fruit.
Many crop plants are grown from seeds that result from bee pollination, e.g. carrots, cauliflowers, celery, onions, broccoli, asparagus. Also bees pollinate plants used as forage or hay for livestock - alfalfa and clover.
The honey bee, Apis mellifera, is the most valuable species used for commercial pollination. It has a strong tendency to visit flowers of the same species on foraging trips, thereby insuring cross-fertilisation.
They can range up to 11km from the hive, and a colony of 20,000 to 30,000 can move large quantities of pollen. They can also be semi-domesticated, and hives can be transported to ensure pollination of commercial crops.
Unfortunately bees and other pollinators are under threat. We have all heard of the biodiversity crisis - loss of species from planet Earth. Most people think of this topic in terms of destruction of tropical rainforest. But biodiversity is under siege everywhere, and therefore so is pollination, one of the most concrete products of the network that arises from biodiversity.
Modern farming methods militate against biodiversity. To take one example, grass-cutting for silage leaves no stubble, unlike traditional methods. Silage cutting destroys surface nests of bumble-bees, drastically reducing the numbers of these important pollinators.
The honeybees themselves are also under attack from the mite Varroa jacobsoni. These mites infest hives and eat the developing bee larvae. Europe generally has a serious mite problem, and it has now reached Britain. Ireland luckily seems to be pest-free so far. The disease is controllable, in its present form, by chemical treatment, but this is expensive.
One in three mouthfuls of the food we eat is prepared from plants pollinated by animals. We are completely dependent on the natural world and we must maintain its good health. It is easy to forget this in our cosy technological world. It is all too comfortable to be concerned about destruction of tropical species by mercenary corporations, while ignoring our own actions in our own backyards.
William Reville is a senior lecturer in biochemistry at UCC