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The indestructable malignant mosquito

Posted in Insects, Medicine, Nature, Plants, Science on Tuesday, 30 August 2011

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This edited article about the mosquito and malaria originally appeared in Look and Learn issue number 1048 published on 10 April 1982.

mosquito, picture, image, illustration

The Mosquito by R B Davis

Anyone who has slept fitfully on a warm night, scratching at the agonisingly itchy swellings appearing on their exposed flesh, knows the sound made by a mosquito. To such a sufferer, the high-pitched whine has a nightmarish quality which he or she will recognise again instantly, even years later.

The mosquito’s hum is produced by the rapid beats, hundreds per second, of its two delicately veined wings. Although this member of the fly family has some 2,500 species, each kind of mosquito has its own wing-beat frequency which distinguishes it from the others. The female’s hum is also slightly lower than the male’s, which means that the sensitive antennae of the male can at once pick up the sound made by a potential breeding partner.

Having detected the female’s signal, the male is irresistibly drawn. Clumps of males will gather on a tuning fork set to the particular musical pitch of the female of their species. A singer who hits the same critical note and holds it for a time can end up with a mouthful of eager male mosquitoes!

Mosquitoes, sometimes known as gnats, are found just about all over the world – only Antarctica seems to be completely free of them. These fragile-looking insects, with their long slender bodies, live almost anywhere where standing water is found. Their habitat can be the edge of salt or freshwater lakes and swamps, a water butt in the garden, or simply a little pocket of water trapped in a rotten tree trunk.

In fact, mosquitoes are such successful insects that they manage to survive under the most unlikely conditions. One species of the insect breeds in the hot, alkaline volcanic pools around Lake Edward in Uganda, and a thriving colony was found in a vat of hydrochloric acid in an Indian factory.

Even the little wells of digestive juice found in carnivorous “pitcher” plants – certain death for most insects – are the breeding site of one remarkable species. Found as far north as Newfoundland, its larvae spend the winter in this fluid, apparently unharmed by the freezing and thawing of the liquid.

Most mosquitoes feed on nectar and other plant juices. That infuriating bite is in fact only inflicted by the female, which uses its piercing mouthparts to obtain the blood it needs in its diet to mature its eggs. This blood can come from animals or humans, but most species prefer one type of host in particular. And if you are one of the unlucky people who have ever wondered why these little nuisances choose you instead of your friend – it is probably because they like the way you smell.

The mosquito’s bite may be irritating to us in Britain, but in many parts of the world it is far more serious. In fact, it can be deadly, for the female insects can spread fatal diseases from one human carrier to another. The tiny organisms which infect humans with malaria are passed on in this way.

The malaria organism, plasmodium, is a parasite which has evolved a life-cycle in which, while breeding in the mosquito, it passes part of its existence in a human bloodstream, in which it destroys red corpuscles.

Since scientists discovered this, the mosquito has been seen as man’s enemy, to be eliminated if possible. Improved living conditions in Britain and western Europe meant that malaria disappeared by itself, but in many parts of the world great efforts have been made to control the disease-carrying insects.

Many different methods have been tried, with varying success. Drainage of swamps, clearing away of plants which provide little pockets of water for breeding, applying a layer of oil to coat the water to prevent the larvae from obtaining oxygen through the surface, and wholesale use of insecticides – all these methods have limited effect, and in some cases can seriously damage the environment. In small areas of water, good results have been obtained by introducing fish which eat larvae and pupae.

Such is its amazing ability to breed and survive, however, that the mosquito is far from extinction. Yet the sight of this slender, elegant insect causes little joy, even to the most ardent conservationist.

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