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Class: B.Sc. HONOURS ZOOLOGY

SEC: Sericulture (Practical Class)

Teacher’s name: Meenakshi Rana

Date: 18th March, 2020

Time: 10:30 AM– 12:30 PM

SERICULTURE

Sericulture is the cultivation of silk through rearing of commercial silkworms. It is an agro

based industry that involves cultivation of food plants for silkworms, rearing of silkworms for

production of cocoons, reeling and spinning of cocoons for production of yarns, for value added

benefits such as processing and weaving. Thus, sericulture generally comprises of three main

branches:

1. Moriculture: Mulberry cultivation. It includes host plant cultivation

2. SILKWORM REARING: It has two branches viz. Grain technology (egg production)

and Silkworm rearing (larval stage management).

Silkworm rearing involves the following six main steps:

1. Disinfection

2. Incubation and Brushing

3. Feeding the Larvae

4. Spacing

5. Bed Cleaning

6. Mounting

3. Silk reeling and Weaving: It is the industrial aspect from cocoon onwards.

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1. Study of different disinfectants used in silkworm rearing houses

It is the most important operation that to be carried out prior to the commencement of rearing.

The use of disinfectants is important not only to get rid of any infection which may be present

in rearing rooms but also as a prophylactic measure. All the rearing equipments and appliances

should be thoroughly washed with water before disinfection.

Disinfection of everything including rearing places is carried out by physical, chemical or

radiation methods.

(i) PHYSICAL METHODS:

These are cheap, convenient and easy to operate.

(a) Sunlight:

Drying of rearing appliances in sunlight can cause disinfection. However, sun drying cannot

be carried out during winter and rainy seasons, and some appliances are likely to be damaged

by exposure to sunlight,

(b) Steam:

Disinfection by steaming may be used for rearing room and some appliances (not made of

bamboo or wood). However, initial cost for installing the steaming apparatus like boiler and

pipeline is high.

(c) Hot air:

It is also a good sterilising method but cannot be used in routine sericulture because of its

production cost.

(ii) CHEMICAL METHOD:

The most commonly used disinfection method in sericulture is chemical method. Chemicals

generally used are:

Non-toxic to man and animals

Broad spectrum activity

Stable and readily mixable with water

Reasonable cost.

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Most frequently used chemicals include chlorine as chloramine, iodine as iodophores, phenol

as cresol and hexachlorophene, formaldehyde as formalin (2%), bleaching powder, etc.

These are used as spray or fumigant. Precautions should be taken during and after the

applications of such chemicals.

DISINFECTION OF REARING HOUSE AND EQUIPMENTS

Before incubation, the rearing room and rearing equipment must be made completely

pathogen free.

Before receiving the silkworm eggs, the rearing house and rearing equipments must be

cleaned thoroughly and washed in 5% bleaching powder solution. It is the most economical

germicide.

Following this rearing equipments are arranged inside the rearing house, doors and windows

are closed airtight and 2% formalin is sprayed using a power sprayer. To disinfect 100 sq.ft. of

space with equipments about 1500 ml of 2% formalin is required and an additional 250ml of

the disinfectant (or more depending on the number of appliances to be disinfected) for the

rearing appliances if they are to be disinfected in the same room. This can be prepared by

mixing one part of 40% formalin with 19 parts of water. Warm water should be used for making

this solution.

The temperature of the room should be above 25 degrees centigrade at the time of disinfection

and for 6 hours after disinfection. For this reason disinfection is usually done before noon.

After spraying, rearing house should be closed for 24 hrs. and opened only next morning.

Care must be taken to seal the holes and cracks in the windows and doors of the rearing room

by pasting paper over them and avoid escape of formalin vapour. The next day, the rooms are

aerated for one day and then sprayed or washed with water to remove the smell of formalin and

to maintain cleanliness.

It is also necessary that proper hygienic conditions are maintained inside the rearing

house/rooms during incubation and rearing.

NOTE: Care must be taken to protect the eyes. Nose and mouth because formalin vapour is

extremely irritating to the mucous membrane.

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2. INCUBATION AND BRUSHING

INCUBATION

Spread the eggs in one layer on a paraffin paper kept on a tray.

Cover the eggs with another paraffin paper.

Maintain the room temperature at 25-26°C and relative humidity at 80%.

When blue pinhead appears, wrap the eggs (25-50 dfls each) in a tissue paper and

keep the eggs inside a black painted box or cover with black cloths or papers for 1-2

days. The eggs are black boxed to aim at uniform development of embryo and

hatching of larvae at a time on a single day.

On the next day, expose the eggs under diffused sunlight or under shade.

BRUSHING OF NEWLY HATCHED LARVAE

Brushing is the separation of newly hatched larvae from their egg shells and transferring them

to rearing trays from the egg cards. The newly hatched larvae are black and bristly.

Brushing is usually starts at 10 am when peak hatching occurs. Brushing can be done by

various ways:

1. Brushing from loose eggs:

Fine meshed net or thin muslin cloth can be placed over the newly hatched larvae. Then

freshly chopped mulberry leaves are sprinkled over that net / cloth. The larvae start to crawl

up through the holes onto the leaves. After sometime, the larvae along with leaves are gently

tapped on the rearing bed.

2. Brushing from egg cards:

From egg cards, newly hatched larvae can be transferred by the following ways:

(i) Feather:

Bird feathers, preferably white ones are used for brushing the delicate newly hatched worms

on the rearing bed. The egg card is held vertically above freshly prepared rearing bed---a

paraffin coated paper kept on a rearing tray and then by gentle strokes of a feather or soft

brush, the larvae are pulled out from the card on the rearing bed. However, this method is

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little bit crude and may cause some injury to the larvae. Feed the larvae with tender leaves

(soft leaves from the apex of the branch) chopped into 0.5-1 cm size.

(ii) Husk:

Here powdered husk is sprinkled over newly hatched larvae on the egg card. Then freshly cut

mulberry leaves are sprinkled over the centre of husk. The larvae crawl up the husk to reach

the leaves. After sometimes, the larvae are brushed from husk by means of a feather or soft

brush on the rearing bed.

NOTE: In all cases of brushing, care should be taken not to touch the newly hatched larvae

with hands. After about two hours of brushing the first feed is given to the silkworm larvae.

NEWLY HATCHED SILKWORM

BRUSHING OF EGGS WITH A FEATHER

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3. Feeding the Larvae

Both the quality and size of the cocoons depend mainly on the quality of mulberry

leaves fed to larvae during rearing. After a little practice, the amount of leaves that is to be

given per feeding to fulfil the appetite of the worms, is adjusted. The amount of food given also

depends on races and voltinism of the moths.

However, maximum amount should be given during the active feeding stage of instar and no

food should be given during moulting. In Indian sericulture, nowadays four feedings per day

is allowed. In case of shoot and floor rearings, three feedings per day are sufficient.

In all larvae, several feeding stages can be noticed during their development:

1. Active feeding stage when larvae feed maximum during the instar

2. Sparsely feeding stage when they eat less, usually at premoulting stage when larvae empty

their gut

3. Non-feeding stage when the larvae do not take any food usually during moulting.

Of the total ingestion during entire larval development, nearly 85% of food is taken during IVth

and Vth instar stages.

LEAF REQUIREMENT (IN Kg) FOR 50 DIFFERENT LARVAL INSTAR STAGES

During feeding, generally a gap of 2 hours is given before and after each moulting.

Young worms are always fed with tender leaves while late stages are given mature mulberry

leaves. To enable the larvae to feed easily, young worms have to be given chopped leaves but

for mature worms, full leaves or young branches or shoots may be given.

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Other Ecological Requirements of Environment for the management of

silkworm larvae

REQUIRED/OPTIMUM TEMPERATURE, HUMIDITY AND SPACE FOR DIFFERENT

STAGES OF DISEASE-FREE LARVAE (DFL)

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4. Spacing

The silkworms grow very rapidly from age to age and increase many times their weight

and size from the previous instar. The total increase in weight from hatching to the end of Vth

instar is about 7,000 to 10,000 times.

Overcrowding of silkworm larvae means insufficient space for movement and free

feeding of the worms and so the larvae crawl over one another. Crowded situation in rearing

trays results in an increase in the accumulation of gases, increased humidity, heat, and

fermentation of litter /fecal matter particularly during the early stage when temperature and

humidity in rearing room are high. This in turn causes under development/unhealthy growth of

larvae, wastage of feeding leaf and unhygienic condition.

If there is space beyond the optimum required, there is a considerable wastage of

mulberry leaves and also the labour costs for feeding increases. The rearing space would vary

in different stages of the silkworm larvae as is evident from the table.

To provide more and adequate space for the growing worm, the rearing space has to be

extended at each stage and this is called spacing. Spacing is usually done along with bed

cleaning and is given once a day.

NUMBER OF TRAYS AND AREA OF SPACE REQUIRED BY DIFFERENT INSTARS OF SILKWORM

DURING REARING

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5. Bed Cleaning

It is done after every moult for the young silkworm larvae and every second day for the

mature/ripe larvae. During 1st instar, bed cleaning should be done once during every moulting,

during 2nd instar twice, once after moult and before next moult. During 3rd instar thrice, i.e.

after moult, before next moult and once in the middle. During 4th and 5th instars once in a day

in case of shelf rearing. However, in case of floor or shoot rearing, bed cleaning should be done

once in each instar.

BED CLEANING METHODS FOR SHELF REARING

Bed cleaning can either be done by:

1. BY HAND

The most conventional and simple method of bed cleaning is by hands as can be seen in the

image on the drawing sheet.

BED CLEANING BY HAND

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2. NET METHOD

To clean the bed, spread a net of 1.5 square cm. over the bed and spread fresh leaves on top of

the net. Larvae will crawl up to feed on the fresh leaves on the net. Transfer the larvae using

the net to another clean disinfected bed/tray. Remove any remaining larvae, then discard the

waste into a composte pile. Spread the larvae well and then feed them.

These nets are made of cotton thread or nylon, woven into nets of different meshes to suit the

size variations of different stages of larvae.

CLEANING BY NET

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3. ROPE METHOD

In rope method, spread 2 m length of rope (two numbers) at parallel row leaving 0.5m

on other side. After 2 to 3 feedings, ends of the ropes are pulled to the centre to make it into a

bundle. Shoot and floor rearing beds are cleaned by this method.

SHOOT AND FLOOR CLEANING BY ROPES

4. By using paddy husk and straw.

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6. Mounting

Mounting is the process of transferring the ripe worms to the mountages. On the

mountage, the ripe worms exude silk, spin the cocoon around itself and transformed into the

pupa inside it. The pupa after metamorphosing into adult moth comes out by piercing open

the cocoon.