Insects are a class of invertebrates belonging to the phylum ARTHROPODA. They have a chitinous exoskeleton, a three-part body, three pairs of jointed legs, compound eyes and one pair of antennae. The class INSECTA or HEXAPODA comprising the insects is the largest class in the phylum arthropoda as well as the most extensive class in the whole animal kingdom.
Insects are a very important group of animals because of their beneficial and adverse effects on the life of man. They have made a tremendous impact on the environment, on human activities and health. Insects can be classified as follows based on their economic importance
Injurious Insects
a) Pests of cultivated plants (crop pests): Each cultivated plant harbours many insect pests which feed on them and reduce the yield of the crop. Field and horticultural crops are attacked by many insect species e.g. cotton bollworm (Helicoverpa armigera), Rice white stem borer (Maliarpha separatella).
b) Storage pests: insects feed on stored products and cause economic loss e.g. Bean weevil (Callosobruchus maculatus), Khapra beetle (Trogoderma granarium).
c) Pest attacking humans, cattle and domestic animals: Cattle are affected by pests like Horse fly (Tabanus atratus), humans by botfly (Dermatobia hominis) (Fleas and Lice). They suck blood and sometimes eat the flesh.
Importance of insects
A) Productive insects
i) Silk worm (Bombyx mori): Helps in the production of silk
ii) Honey bee (Apis mellifera): provides us with honey and other products like bee wax and royal jelly.
iii) Lac insects: secretions from the body of these scale insects are called lac. It is used in the making of vanishes and polishes.
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B) Insects useful as drugs, food, ornaments etc.
i) As medicinei) Silk worm: - The silk worm filament secreted from the salivary gland of the larva helps us in producing silk.
ii) Honey bee: - Provides us with honey and many other by-products like bees wax and royal jelly.
iii) Lac insects: - The secretion from the body of these scale insects is called lac. Useful in making vanishes and polishes.
b) Insects useful as drugs, food, ornaments etc.
i) As medicine e.g. Sting of honey bees- remedy for rheumatism and arthritis, Eanthoridin extracted from blister beetle –useful as hair tonic.
ii) As food - for animals and human being.
For animals - aquatic insects used as fish food.
Grass hoppers, termites, pupa of moths. They have been used as food by human beings in different parts of the world.
(c) Ornaments, entertainers
Artists and designers copy colour of butterflies.
Beetles worn as necklace.
Insect collection is a hobby
(d) Scientific research
Drosophila and mosquitoes are useful in genetic and toxicological studies respectively.
Helpful Insects
(i) Parasites: These are small insects which feed and live on harmful insects by completing their life cycle in a host and kill the host insect. E.g. egg, larval and pupal parasitoids
(ii) Predators: These are large insects which capture and devour harmful insects. E.g. Coccinellids, Preying mantis.
(iii) Pollinators: Many cross-pollinated plants depend on insects for pollination and fruit set. E.g. Honey bees, aid in pollination of sunflower crop.
(iv) Weed killers: Insects which feed on weeds and kill them. E.g. Parthenium beetle eats on parthenium. Cochneal insect feeds in Opuntia dillenii.
(v) Soil builders: soil insects such as ants, beetles, larva of cutworms, crickets, collembola, make tunnels in soil and facilitate aeration in the soil. They become good manure after death and enrich soil.
(vi) Scavengers: Insects which feed on dead and decaying matter are called scavengers. They are important for maintaining hygiene in the surroundings. E.g. Carrion beetles, Rove beetles feed on dead animals and plants.
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Household and Disease Carrying Insects
i) Pests which cause damage to belongings of human beings like furniture, wool, paper etc. E.g. Cockroaches, furniture beetle, sliver fish, etc.
ii) Pests which cause painful bite, inject venoms. E.g. Wasps, bees sting us. Hairy caterpillar nettling hairs are poisonous. Mosquitoes, bugs bite and suck blood from us.
iii) Disease-causing: Mosquito - Malaria, Filariasis, Dengue fever. Housefly- Typhoid, Cholera, Leprosy, Anthrax
Later I will talk on the various classes of the anthropoda phylum.. also watch out for tutorial on nursery creation.