Beneficial and harmful insects

Productive insects (Silkworm, Honey bees, Lac insects)

Sericulture is an agro-based industry. It involves rearing of silkworms for the production of raw silk, which is the yarn obtained out of cocoons spun by certain species of insects. The major activities of sericulture comprises of food-plant cultivation to feed the silkworms which spin silk cocoons and reeling the cocoons for unwinding the silk filament for value added benefits such as processing and weaving.

Five varieties of silk worms are reared in India for producing this natural fibre. Bombyx mori, the silk worm, feeds on the leaves of mulbery to produce the best quality of fibre among the different varieties of silk produced in the country. Antherea assama is confined to only Brahmaputra Valley of India in the world. It produces the famous muga silk. Tasar silk is a product of Antherea mylitta, which feeds on Terminalia tomentosa grown in the thick jungles of Bihar, Madhya Pradesh and Orissa. The recent introduction of Antherea royeli and Antherea perniyi has enabled the country to produce the oak tasar silk, Phylosamia ricini, the eri silkworm, which feeds on Ricinus communis, is raised in Assam and Orissa commercially. Of the total production of 2,969 tonnes of silk in India, as much as 2,445 tonnes is produced by the mulberry silkworms, Bombyx mori.

Lac Insect any of the species of Metatachardia, Laccifer, Tachordiella,Austrotacharidia, Afrotachardina, and Tachardina of the superfamly Coccoidea, order Homoptera that are noted for resinous exudation from the bodies of females. Members of two of the families viz. Lacciferidae and Tachardinidae appear to be more concerned with lac secretion. There are several lac insects, some of which secrete highly pigmented wax. The Indian lac insect Laccifer lacca is important commercially. It is found in tropical or subtropical regions on banyan and other plants.

The females are globular in form and live on twigs in cells of resin created by exudations of lac. Of the many species of lac insect, Laccifer lacca, (=Tachardia lacca) is the commercially cultured lac insect. It is mainly cultured in India and Bangladesh on the host plant, Zizyphus mauritiana and Z. jujuba. The insect starts its life as a larva or nymph which is about 0.6 mm long and 0.25 mm wide across the thorax. The young settles down on a suitable place of the host plant gregariously. On the average some 150 of such larvae may be present per square inch of the twig.

Apiculture or beekeeping is the maintenance of honey bee colonies, commonly in hives by a beekeeper in apiary in order to collect honey and beeswax, and for the purpose of pollinating crops. The genus Apis is comprised of a comparatively small number of species including the western honeybee Apis mellifera, the eastern honeybee Apis cerana, the giant bee Apis dorsata, and the small honeybee Apis florea.

Nectar is a sugar solution produced by flowers containing about 80% water and 20% sugars. Foraging bees store the nectar in the ‘honey sac’ where the enzyme invertase will change complex sugars into simple sugars called mono-saccharides. Upon return to the hive, the foraging bee will disgorge the partially converted nectar solution and offer it to other bees. Housekeeping bees will complete the enzymatic conversion, further removing water until the honey solution contains between 14 – 20% water.

Human food value

There are 1,462 recorded species of edible insects. Doubtless there are thousands more that simply have not been tasted yet. 100 grams of cricket contains: 121 calories, 12.9 grams of protein, 5.5 g of fat, 5.1 g of carbohydrates, 75.8 mg calcium, 185.3 mg of phosphorous, 9.5 mg of iron, 0.36 mg of thiamin, 1.09 mg of riboflavin, and 3.10 mg of niacin. Compare this with ground beef, which, although it contains more protein (23.5 g.), also has 288.2 calories and a whooping 21.2 grams of fat. Usually crickets, grasshoppers, beetle and moth larvae and termites are eaten. Australian aborigines regularly ate honey pot ants, adult bogong moths and the larvae of wood moths.

Being rich source of protein, grasshoppers have been eaten in nearly all regions of the world. They are a common food in parts of Asia and Africa—fried, roasted or ground to be mixed with flour. The grasshoppers eat green plants, however, by far outweighs their value as food. Insects are an important food for many vertebrates, including birds, amphibians, reptiles, fish and mammals. These “insectivorous” vertebrates usually feed on many insect species, and rarely focus on specific pests, unless they are very abundant.


 Ants, beetles, apterygotes, cockroaches, crickets and a large number of other insects thrive on dead carcasses, left over organic matter or excreta and in the process clean the environment. Economic losses avoided every year by the burial of livestock waste by dung beetles only are estimated to be over $3.8 billion.


Majority of insects, almost 98% of all insect species, live in low populations in different ecosystems, without causing appreciable damage. But they form an important component of the food web and work unnoticed. Conservation of such fauna is important since we do not know the interactions of such insects with the animal and plant species.


Less than 1% of insects are regarded as pests. They can be classified into the following categories.

Pests of agriculture and forestry (Locusts, caterpillars, bugs, hoppers, aphids etc.)

Locusts are among the most destructive of all insect pests. Swarms of desert locusts were among the plagues of the Biblical Egyptians, and they still plague farmers throughout Asia and Africa. Their threat is so great that regional and international organizations monitor desert locust populations and launch control measures when necessary.

Locusts are particularly destructive in hot, dry regions when a sudden increase in their numbers, combined with food shortage, forces them to migrate. They migrate in huge swarms, devouring virtually every green plant in their path.

Pests of stored grains

The most common insect pests of stored cereal grains are:

Rice Weevil (Sitophilus oryzae); Lesser Grain Borer (Rhyzopertha dominica);

Rust Red Flour Beetle: (Tribolium spp.); Sawtooth Grain Beetle: (Oryzaephilussurinamensis); Flat Grain Beetle: (Cryptolestes spp.); Indian Meal Moth (Plodiainterpunctella); Angoumois Grain Moth (Sitotroga cerealella); Khapra beetle (Trogoderma granarium); Rice moth (Corcyra cephalonica).

Insect management for stored grain depends upon good sanitation and grain storage practices. Clean storage areas to reduce the potential for insect migration into the new grain. Once the grain is dried to 13 percent moisture or less, cool it as soon as possible by running aeration fans. Reducing the grain temperature to less than 60ºF stops insect reproduction, and lowering it to less than 50ºF stops insect feeding activity. Infested grains should be fumigated by Aluminum phosphide (Phostoxin, Fumitoxin), which is best in most circumstances. Methyl bromide may also be used.

Household pests (carpet beetles, furniture beetles, cloth moth, termites and silverfish)

Common household pests include ants, termites, bed bugs, carpet beetles, furniture beetles, book lice, house flies, fleas, cockroaches, silver fish, clothes moths and spiders – the list seems almost endless. Common household pests enter our homes for shelter and food, and also to nest and breed. Common household pests can cause damage to our homes especially clothes, eatables and furniture. Household pests can also be a threat to health of our families by spreading bacteria, diseases or allergens in our homes. Household pests can be irritating, annoying or irritating and annoying. They can be controlled by spraying insecticides or by fumigants and by maintaining hygiene.

Insects of medical and veterinary importance (Mosquitos, flea, beetles, flies)

Mosquitoes can spread diseases such as malaria, yellow fever, dengue fever. Tsetse flies spread sleeping sickness. Lice suck human blood and can cause sores, which if left untreated can become infected which may lead to blood poisoning.

Screw worm flies lay their eggs in the wounds of farm animals and pets. Horseflies and black flies suck blood and have painful bites, which can become infected. Houseflies spread germs and spoil meat by laying eggs in it. Bubonic Plague (or Black Death) was the worst disease epidemic in human history. It took 14 million lives–nearly 1 out of 4 people–in 14th-century Europe. The plague is passed to humans by the bite of the Oriental rat flea (Xenopsylla cheopis), which picks up the disease-causing bacteria from rats.

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