Chawki Rearing:-       Ngangshimeyu  Extension Officer.

 

Chawki rearing is the rearing of first two instars of silkworm under healthy and hygienic condition. The object of chawki rearing is to ensure healthy batch of vigrorous growing silkworms that will spin successful cocoon crops in later stages with minimum of loss due to diseases.

Characteristics of young silkworms:

 

Young silkworm need more care and attention  as their resistance to disease is low.

Effect of pesticides, chemicals and gases are more injurious during 1^st instar.

They require high water content in food plants.

Growth rate of the larvae is very fast.

 

Disinfection of rearing house & equipments:

Before chawki rearing, rearing house and rearing equipments must be cleaned in 5% bleaching powder solution. Then 2% formalin is sprayed under closed doors and windows.

 

Uniform hatching of eggs:

Egg should be kept in darkness since light  has profound effect on egg hatching.

Egg should be kept in black box for one or two days before hatching.

On the day of hatching, egg should be exposed to light to get uniform hatching.

 

Brushing:

Brushing is the process of separating the newly hatched larvae gently and carefully from the egg sheets. Chopped tender leaves are to be sprinkled on newly hatched larvae.

Feeding:

Generally four times a day is ideal. Leaves should be chopped in order that they are supplied to silkworm evenly. The size of the chopped leaves are variable according to the larval stage.

 

Environmental conditions:

 

Temperature:

 Optimum temperature for chawki rearing is 27-28ºC for 1^st instar and 26-27ºC for 11 and 111 instars.

Very high and low temperature imbalances the metabolic activity and the silkworm becomes unhealthy.

Remedy:

Low temperature can be increased by using electric heaters.

High temperature can be brought down by sprinkling water etc.

 

Humidity:

High humidity makes the length of growing period of silkworms short, whereas low humidity makes the length of growing period longer, low humidity causes drying leaves, reduces consumption, retards larval growth and larvae becomes weak and easily susceptible to diseases.

Remedy:

Keep clean, pathogen free and wet foam pads around the rearing bed.

Use paraffin paper or blue polythene sheet as bottom and covering sheets in the rearing tray to conserve humidity.

Light:

Silkworm requires a minimum of 16hrs. light per day.

Silkworm prefers dim light (15-30) lux.

 

Aeration:

Fresh air is required for silkworms.

 

The rearing room is polluted by  carbon monoxide, ammonia etc due to metabolic activity of the silkworm.

Stagnation of air should be avoided by proper ventilation.

High moisture in the bed harbours fungus and other pathogens.

Spacing:

Optimum spacing for young age worms in the 1^st 3 instars are as follows for 100 layings which contain an average of 400 eggs per layings.

Age of the worm	Area of bed(sq.ft) Beginning.	Area of bed(sq.ft) End.	Increase in spacing during the instar.
1	4	15	3½ times
11	15	45	3 times
111	45	90	2  times.

From the above table it is seen that spacing is required  to increase systematically at every stage of growth of chawki worms. The object in doing so is to ensure maximum development of all the larvae uniformly by providing required space as they grow.

Bed cleaning:

Bed cleaning is the removal of old leaves, fecal matter of silkworms, dead worms etc from the rearing bed. It is very difficult because mishandling causes increase in missing percentage of the silkworms. So, utmost care is necessary during bed cleaning. During 1^st instar bed cleaning may or may not be done. In 2^nd instar one cleaning is suggested. Three times bed cleaning is required in 3^rd stage.

Moulting care:

 

Under optimum rearing conditions, the worms take 12-14 feeding to settle for 1 moult, 8-10 feeding for the 2^nd moult and 10-12 feeding for 3^rd moult. As signs of moulting are observed and as soon as few worms have settled, every effort should be made to assist the moulting. Moulting duration is 20-24 hrs. During moulting, rearing bed should be thin and dry. More humidity is harmful for moulting.