Invertebrates

Silkworm

Classification:

Kingdom – Animalia

Phylum – Arthropoda

Class – Insecta

Type – Silkworm

External structure

1. An adult silkworm is about 25 cm long.
2. Creamy white in color.
3. Body is divisible into head, thorax and abdomen.
4. Two pairs of wings, three pairs of leg are present.
5. A pair of compound eyes, a pair of antenna ore present in their head.
6. Abdomen of female is larger than of male.

Sericulture: Commercial farming of silkworm is called sericulture. Types of silkworm cultivated in Nepal

1. Seri (bombyx mori) – Feeds on mulberry leaves.
2. Eri (attacus ricini) – Feeds on castor leaves.

Life cycle of silkworm

Life cycle of silkworm completed in 4 stages:

1. Egg
2. Larva
3. Pupa
4. Adult

Egg: 

1. Female silkworm lays about 300 eggs on mulberry leaves.
2. Eggs are pin head in size, white coloured.
3. When these eggs are kept in 18-25°C temperature for 10-12 days, larva hatch out.
4. In winter, eggs of silkworm are stored in cold place to avoid their hatching as mulberry leaves are not available.

Larva: 

1. They are about 6mm long when hatch out, and reach to length of about 8cm when grown fully.
2. They feed continuously on mulberry leaves.
3. They moult 4 times in their life.
4. After 4th mounting salivary glands are developed and became active.
5. These glands secrete special fluid which when come to contact with air get dry and form silk thread.
6. Larva moves his head in such a way that it wrapped its body by silk and form oval capsule which is cocoon and change into pupa.

Pupa:

1. It is inactive stage in life cycle of silkworm.
2. Metamorphosis take place in this stage.
3. Metamorphosis is the rapid transformation of larva into adult during life cycle of insects is called metamorphosis.
4. Pupa state completes in about 12-14 days. To extract silk thread of cocoons are boiled in hot water which kills pupa inside it so that it doesn’t damage silk thread while coming outside the cocoon.

Adult(Imago): 

1. After full development adult silkworm come out from cocoon. 
2. Male Silkworm die after mating where as female silkworm can live for 5-7 days and die after laying eggs.

Importance of silkworm

Silkworm are called queen of fibre as it produce best quality natural fibre which are long, strong, smooth, elastic, attractive and durable so high quality clothes can be prepared from them and it has very high demand in international market, so farmers can improve their economic condition through sericulture.

Honey bee:

Classification 

Kingdom – Animalia

Phylum – Arthropoda

Class – Insecta

Type – Honey bee

There are 3 types of honey bee in the colony

1. Queen Bee
2. Worker bee
3. Drones

Queen bee

1. It is the largest bee in the colony (swarm).
2. There is only one queen bee in a colony.
3. Queen is a single egg laying female bee in hive.
4. Queen produces special scent which is received by all other bees for their identity.
5. Queen bee co-ordinates and maintains unity in a hive.

Workers

1. Workers are the smallest bee in a hive.
2. Workers are infertile female bee.
3. Workers are busiest bees in hive.
4. Workers collect pollen and nectar, prepare comb, protect, clean hive, feed larva.

Drones

1. Drones ate fertile male bees.
2. Their function is take part in making and fertilize the queen.
3. They are smaller than queen but bigger than workers.
4. The number of chromosomes in drones are half to that of worker and queen.

Life cycle of honeybee.

Life cycle complete in 4 stages

1. Egg
2. Larva
3. Pupa
4. Adult

Egg: 

1. New queen bee takes part in mating flight called ‘Nupital flight’ with several drone and mating takes place in air. After mating drones die but queen return back to hive and start laying eggs after 2 to 3 days.
2. Queen lays about 3,000 eggs in 1 day.
3. Eggs are elongated, white in colour.
4. Queen lays two types of egg, Fertilized and Unfertilized.
5. Egg stage competes in 3 days.

Larva: 

1. Larva stage of queen bee completed 5-6 days, where as larva stage of worker and drone completes in 6 days.
2. When larva form unfertilized eggs are fed royal jelly in first 3 days and then honey and bee breeds, it develops into Drone.
3. When larvae from fertilized eggs are given only royal jelly for whole period, it develops into queen.
4. When larva from fertilized eggs are fed royal jelly for first 3 days and then bee bread and honey, it develops into worker.

Pupa: 

1. It is inactive stage in which metamorphosis take place. 
2. Pupa of queen bee completes in 7.5 days, worker bee in 12 days and drone: bee in 14.5 days.

Adult: 

Adult bee emerges from pupa after complete metamorphosis and remains busy in different activities.

Economic importance of honey bee:

1. Honey bee are the source of honey which is rich in vitamins, minerals and other nutrients so used as tonic or body. It is also used as a medicine so it has very high demand in market.
2. Wax prepared by honey ball is used to make various medicines, cosmetics etc.
3. Honey bees are vital pollinators they help in pollination increasing the production of fruits and vegetables.

Solved exercise

a. Write 2 differences between larva of silk worm and larva of honey bee.

b. Write 2 differences between egg of silk worm and egg of honey bee.

c. Write 2 differences between silk worm and honey bee.

d. Give reason why queen grows faster than other types of bees.

It is because queen bee is given only royal jelly during larva stage which is highly nutritious.

e. Give reason why at pupa stage, silkworms are killed to get fibre.

When silkworms aren’t killed in pupa stage, after complete development, they come out from cocoon creating hole in it which damages the silk thread. So to avoid this they’re killed in pupal stage.

f. Give reason why silk moth is called queen of fibre.

Since silk moth produces best quality natural fibre which are long, shiny, smooth, soft, flexible and attractive they are called queen of fibre.

g. Define apiculture and apiary.

Commercial farming of honeybee is called apiculture or bee-keeping.

A Location where bees are kept is called apiary.