Posts Tagged 'Entomology'

Of Insects & Men

An Article by Mohan Pai

Of Insects & Men


 

“Go to the ant, thou sluggard – consider her ways and be wise ….”
– King Solomon

 

Insects have evolved from their wormlike ancestors some 350 million years ago and have been around for a much, much longer period than other forms of life like the reptiles and the mammals and the late comer Homo sapiens (only 2-3 million-year old). Cockroaches (Blattodea), for instance have been around since the upper Carboniferous (300 million years). There are only a few terrestrial habitats and niches that have not been occupied by some group of insects, and a few climatic conditions to which none have become adapted. Even the arctic zones have a sizeable insect fauna (especially flies) even though activity and reproduction in theses extremes is limited to a few months only.
Insects (Class Insecta) are a major group of arthropods and the most diverse group of animals on the Earth, with over a million described species—more than half of all known living organisms—with estimates of undescribed species as high as 30 million, thus potentially representing over 90% of the differing life forms on the planet. Insects may be found in nearly all environments on the planet, although only a small number of species occur in the oceans, a habitat dominated by the other arthropod group of crustaceans.

Bottle-fly

There are approximately 5,000 dragonfly species, 2,000 praying mantis, 20,000 grasshopper, 170,000 butterfly and moth, 120,000 fly, 82,000 true bug, 360,000 beetle, and 110,000 bee, wasp and ant species described to date. Estimates of the total number of current species, including those not yet known to science, range from two million to fifty million, with newer studies favouring a lower figure of about six to ten million. Adult modern insects range in size from a 0.139 mm (0.00547 in) fairyfly (Dicopomorpha echmepterygis) to a 55.5 cm (21.9 in) long stick insect (Phobaeticus serratipes). The heaviest documented insect was a Giant Weta of 70 g (2½ oz), but other possible candidates include the regius and Goliath beetles Goliathus goliatus, Goliathus Cerambycid beetles such as Titanus giganteus, though no one is certain which is truly the heaviestThe study of insects (from Latin insectus, meaning “cut into sections”) is called entomology, from the Greek e?t?µ??, also meaning “cut into sections”

The overwhelming success of insects is due to at least six major assets that they developed in the endless quest for survival: an external skeleton, small size, flight, metamorphosis, specialized system of reproduction and adaptability, Insects are a living example of the validity of what man now appears to have grasped as truism – “Small is Beautiful”. Unlike ourselves, the demands of insects from our environment (with mostly non-renewable resources) are meagre. The fact that insects were the first animals to develop wings for flight, and that most have still retained, if not perfected them, is a great asset to their overwhelming success. Flight has enabled them to escape from enemies in a jiffy, to traverse large distances to find food and to search efficiently for their mates, besides other obvious advantages.The development of metamorphosis has enabled insects to divide their life stages into four distinct phases and structural adaptations. This kind of pattern has allowed insects to adopt two completely different life-styles – a sort of ‘Dr. Jekyll and Mr. Hyde’ character, so to speak; the larval and adult stages being able to exploit entirely different food sources and life-styles, to distinct advantage. Unlike humans, who spend only a fifth of our life-span as “immatures”, insects spend almost all their time as inconspicuous and admirably adapted larvae or nymphs; the adult period, efficiently being used only for males and females to find each other, mate and reproduce, ensuring the next generation, which is all that life is really about. On this critical requirement for a generally bisexual living entity, insects have achieved wonders that man still is fumbling for. Winged adults are able to delay fertilization of the egg, even after mating has occurred (by storing the male’s sperm cells in a little sac called spermatheca until the female is able to find proper environmental conditions and food for her young).

Termite mound made by cathedral ants

Social insects (termites, bees, ants, wasps) have even developed ways and means to produce ‘boys or girls’ and even different ‘castes’ to suit, not their fancy, but their genuine requirements !Plants provide food for a great host of insect groups. Leaves are a common plant part that insects consume and some species are remarkable defolators of whole trees. Many other insects live on or inside bark or timber of trees and many species of insects specialize in being ‘undertakers’ which feed on dead plant matter. Most plant that flower have come to depend on special kind of insects to help them in pollination and hence in their regeneration.

Insectivorous plants, on the other hand entice and feed on insects.Insects also have associated themselves with vertebrate animals, either as their food or as their hosts. Some insects have developed into blood-feeders (Mosquitoes & Biting flies) and these cause irritation by their bites in addition to loss of blood. More importantly, insects also assume the role of dangerous vectors of a variety of animal and human diseases.

Predation is widespread among insects and it takes several forms according to the insect group in which it occurs and the prey they attack. Mantids, for instance, wait inconspicuously and motionless for their prey to come within reach of their prehensile forelegs. Dragonflies are master predators of the air, consuming their prey while in flight. Many insects have become parasitic, especially on other insects which they help to keep in tolerable population limits. Much of the parasitism is of special type, which results in the host being completely consumed and in its death. The other is where the host is allowed to survive by the parasite which is in its favour.Most courses in Entomology deal with insects as enemies of man. We have studied insects in the field, classroom, laboratory mainly with the objective of finding ways and means of dealing with the pestiferous species that have hounded us from time immemorial.

To quote American entomologist, S. A. Forbes:

“The struggle between man and insects began long before the dawn of civilization, has continued without cessation to the present time, and will continue, without doubt, as long as the human race endures. It is due to the fact that both men and certain insect species constantly want the same things at the same time. Its intensity is owing to the vital importance to both, of the things they struggle for, and its long continuance is due to the fact that the contestants are so equally matched. We commonly think of ourselves as the lords and conquerors of nature, but insects had thoroughly mastered the world and taken full possession of it long before man began the attempt. They had, consequently, all the advantage of a possession of the field when the contest began, and they have disputed every step of our invasion of their original domain os persistently and so successfully that we can even yet scarcely flatter ourselves that we have gained any important advantage over them. Here and there a truce has been declared, a treaty made, and even partnership established advantageous to both parties of the contract – as with bees and silkworms, for example; but wherever their interests and ours are diametrically opposed, the war still goes on and neither side can claim a final victory. If they want our crops, they still help themselves to them. If they wish the blood of our domestic animals, they pump it out of the veins of our cattle and our horses at their leisure and under our very eyes. If they choose to take up their abode with us, we cannot wholly keep them out of the house we live in. We cannot even protect our very persons from their annoying and pestiferous attacks, and since the world began, we have never yet exterminated – we probably never shall exterminate – so much as a single insect species. They have, in fact, inflicted upon us for ages the most serious evils without our even knowing it”.

Reality in nature (of which man is an integral part) teaches us the fact that while insects do not need man for their survival, man would face certain extinction if insects were to be removed from his ecosystem .Insects belong to pestiferous species (mosquitoes, bedbugs, biting flies, fleas, animal lice) and beneficial species (honeybees, silkworms, lac insect, mealybug, etc.) 

Grass hopper

The beneficial species do a great deal for man.

0 Pollination, not only of man’s commercial plants, but also of many wild plants that make up the local flora which are important components of the ecosystem, is perhaps the most beneficial act that insects perform in man’s favour. Insects are responsible for many, if not most, of our fruit, vegetable, ornamental and field crops setting fruit after they pollinate the flowers.

0 The next important task through which insects do us a great amount of good, is by fighting among themselves. The poisonous chemicals that man is compelled to employ (even though they are hazardous to him and his environment), are insignificant tools compared to the multitudinous hordes of insect friends that kill and feed upon his enemies as a daily chore !This predation is the greatest single factor that prevents plant feeding insects from out-competing and overwhelming the rest of the living world is that they attacked and fed upon by other insects. As a hypothetical example, if just one pair of house-flies were able to produce normally, resist disease and combat their natural enemies, they would, in just five or six months, cover the entire planet Earth 50 feet high with their progeny ! But the balance that exists in nature never allows this to happen.

0 Insects are useful to man in their value as food, direct or indirect.

Owing to their huge numbers, though of small size, insects probably exceed all other animal matter (biomass on earth in weight on land. The birds alone probably depend on insects for two-thirds of their food requirements. Many of our commercial fish species subsist largely on aquatic insects. Many animals, especially those like pigs (meat) and fur animals, eat white grub and other insects .Man has survived on insect food in his early evolutionary history, and even now some of our primitive and tribal races delight their palate by eating insects such as termites, grasshoppers, crickets, beetles, caterpillars, ants, etc.

0 Some varieties of insect feed on and destroy plants (weeds) that are harmful to man’s interest.

0 Millions of individuals of subterranean species of insects that live below ground (as immatures or adults, or both) help to improve physical condition of the soil and promote its fertility. Insects help to break up rock particles and expose them to the action of water and other weathering influences by bringing them up to the soil surface. The numerous underground tunnels made by insects facilitate the circulation of much-needed air into soil that is essential for good health of plants. They also add valuable organic matter and humus to soil. Even their dead carcasses accumulating on the soil surface are a great source of fertilizers to plants. Their excreta, in chemical content and in mere volume, far exceeds anything that man or any of the larger animals, in unison, can incorporate into soil.

0 Some of the most helpful insects are those that dutifully perform their role as scavengers of ‘nature’s waste. First, they remove from the surface of the earth the dead and decomposing bodies of plants and animals, converting them into simpler and more assimilable compounds, removing what otherwise would be a health menace. Secondly, they convert they convert dead plants and animals into simpler substances that could then be reused by growing plants as food. Man may find these scavenging animals repulsive, but without them the world would be a cesspool.

0 In medieval ages, almost every insect was supposed to be of medicinal value. Most of these beliefs have now found to be based on superstition. However, some of Insects also produce useful substances such as honey, wax, lacquer and silk. Honey bees have been cultured by humans for thousands of years for honey, although contracting for crop pollination is becoming more significant for beekeepers.

The silkworm has greatly affected human history, as silk-driven trade established relationships between China and the rest of the world. Adult insects such as crickets, and insect larvae of various kinds are also commonly used as fishing bait..Insects have taught man a great many things and have helped him to solve some of the most puzzling problems in natural phenomena. They have also led the way to some of man’s remarkable inventions. The ease of handling them, their rapidity of multiplication, great variability, and low cost of maintenance and rearing, have made insects the ideal experimental animals for the study of physiology, biochemistry and ecology.

The foundation of modern genetics have been derived from studies of the lesser fruit-fly of the genus Drosophila. Studies of variation in populations of single species, geographical distribution, and the relation of colour and pattern to ecological habitat or other surroundings have been greatly advanced through the study of insects, as has the geological history of the earth (continental drift) and a better picture of the planet’s living inhabitant’s evolution. Principles of polyembryony and parthenogenesis have also been discovered by the study of insects.

The behaviour and psychology of higher animals (including man) have been illuminated by a study of the reaction of insects such as the honeybee, and valuable lessons in sociobiology for us have been deduced from a study of the economy of social insects. Insects are also used as an index for stream pollution and such important factors in conservation of our natural resources.

Sources: Encyclopedia Of Indian Natural History by R. E. Hawkins, Wikipedia.

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http://delhigreens.com/2008/03/10/whither-the-wilderness/
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