In addition to numerical abundance, insects also abounds in number of species. A swarm of insects locusts contain more than 150,00,00,000 individuals. Aphids or plant lice are so abundant that would be 25,00,000- 30,00,000 per plants. Special adaptation for reproduction are present in most insects. For instance, in the notorious cottony cushion scale Icerya purchasi injurious to orchard, each female lays at a time 500-1500 eggs and there are 3-4 brood every year. So even if only 200 survive the total number at the end of the 4th generation would theoretically be 16,00,00,000,00,000 . Mention may be made of the traditional example of house fly where a pair beginning to breed in April, would, if all young's survive, result in total of 191,010,000,000,000,000,000 by August and this number would be sufficient to cover the earth 47 feet deep.
In another research findings if a pair of house fly can breed spontaneously and if every progeny can survive (imaginary) and after one year if every individual can placed one after another, that length would be as 2,40,000 mile (equivalent to the distance from earth to moon)
The eggs of most insects are well protected and special methods of reproduction by polyembryony, parthenogenesis step up this multiplication.
Of all the adaptations, it is in the nature of the body coverings, the chitinous exoskeleton that offers the insects maximum advantages. It is strong and rigid and at the same time flexible.
Distribution of Insects:
Insects enjoy a wide distribution from equator to pole. They are found on snowy mountain of the Himalayas ,deep beneath of soil ,in deserts, hot spring , fresh water and the sea. This wide distribution are correlated with favorable conditions. They can survive up to lower temperature up to – 460C . They have a great migratory power. Some insect can survive in the cork of cyanide poison.
Distribution is brought about by migration and in many cases through air current. Man himself with the expansion of trade, spread both beneficial and harmful insects.
Man has been attracted by insects from very early times. In ancient India, philosophical commentaries and literature mention about insects.
Use of Insects:
Use of insects and insects products as items of medicinal value (oil beetles, lac, use of red ants in suturing wound where a biting ant in decapitated to hold fast the gape of wound) have found a place in certain indigenous system of treatment. Honey is used more as medicine than as food. Parts of insects have been used as cheap jewellery by certain tribes.
Insects for Food & Feeds:
Trends towards 2050 predict a steady population increase to 900 corer people, forcing an increased food/feed output from available agro-ecosystems resulting in an even greater pressure on the environment. Scarcities of agricultural land, water, forest, fishery and biodiversity resources, as well as nutrients and non-renewable energy are foreseen.
Edible insects contain high quality protein, vitamins and amino acids for humans. Insects have a high food conversion rate, e.g. crickets need six times less feed than cattle, four times less than sheep, and twice less than pigs and broiler chickens to produce the same amount of protein. Besides, they emit less greenhouse gases and ammonia than conventional livestock. Insects can be grown on organic waste. Therefore, insects are a potential source for conventional production (mini-livestock) of protein, either for direct human consumption, or indirectly in recomposed foods (with extracted protein from insects); and as a protein source into feedstock mixtures.
Since 2003, FAO has been working on topics pertaining to edible insects in many countries worldwide. FAO ’s contributions cover the following thematic areas:
the generation and sharing of knowledge through publications, expert meetings and a web portal on edible insects;
awareness-raising on the role of insects through media collaboration (e.g. newspapers, magazines and TV);
the provision of support to member countries through field projects (e.g. the Laos Technical Cooperation Project);
networking and multidisciplinary interactions (e.g. stakeholders working with nutrition, feed and legislation-related issues) with various sectors within and outside FAO .
Undoubtedly insects occupy a dominant position in the animal world. Of the estimated 15,00,000 species of animals, around 10,00,000 are insect. Their tenacity for life is amazing and their capacity for multiplication and wonderful adaptation has made them a serious threat to human beings. They have a great capacity for flight; this has enabled them to migrate and get dispersed. Their ability to live in extreme of environmental stress and this ability to invade and colonize almost every nook and corner of whole world.
Not only are they abundant in places where green vegetation is luxuriant, they are also found in dead and decayed organic matter, they also exists as parasites of animals, including insects. They are known to live in crude oil, petroleum, and even in the cork of cyanide bottles that are used to kill them.
Their small size confers many advantages. Because of their small sizes, they occupy very little rooms even if millions of individuals are crowded in a place though they consume very small quantities of food but the combined effect of their effect of their attack on the host can be very effective.
Insects feed on all parts of a tree
Some Common Insects That Damage Trees:
1. Lace bug sucking sap from a leaf.
2. Gall wasp feeding in a leaf gall.
3. Tip moth boring in the tip of a branch.
4. Scale insects feeding on sap from leaves and shoots.
5. Twig girdler biting through a branch.
6. Egg case of a tent caterpillar on a branch
7. Twig swollen by a gall insect.
8. Red spider mite feeding on a leaf.
9. Leaf folded and deformed by thrips feeding.
10. Aphid feeding on a plant sap.
11. Bark beetle boring into a stem.
12. Caterpillar chewing on a leaf.
13. Long-horned beetle and round headed borer
boring in stem.
14. Leaf miner feeding between leaves.
15. White grub feeding on roots.
Yet trees survive and perpetuate themselves. A daily contest occurs between trees and insects. Insects have developed habits, capabilities, and body parts that allow them to attack a tree, but trees have developed a number of defense mechanisms.
Insects are distinguished from other types of animals by having certain structural features
The Characteristic Body Parts of Adult Insects
The possession of antennae, head, thorax, abdomen, 3 pairs of legs and usually 1 or 2 pairs of wings separates adult insects from similar animals like mites, spiders, and lobsters. Also, insects develop through a progression of growth stages
In the usual sequence the adult female insect lays eggs. A larva or nymph emerges from each egg. Nymphs grow and molt several times before becoming adults. Larvae grow and molt to an intermediate (pupal) state. After a period of time an adult insect emerges from the now empty shell of the pupa.