Mulberry Silkworm Rearing and Farming
Sericulture is an agro-based industry, and it deals with mulberry culture and silkworm rearing. The rearing of silkworm involves the following steps.
- Preparation of rearing silkworm.
- Collection of race.
- Sterilization of eggs.
- Egg incubation.
- Larvae rearing.
- Ripening, spinning, and cocoon formation.
- Cocoon harvesting.
1. Preparation of rearing silkworm: The rearing room and appliances used for rearing must be thoroughly cleaned and disinfected with 24% formalin. Before disinfecting the rearing room, all crevices and holes should be filled.
2. Collection of race: Selection of sericulture board recommended race of diseased free silkworm cocoon.
3. Mating: Pairs adults just after emergence from the cocoon by covering glass funnel and removing male silkworm from the female after mating. Immediately after copulation, females start to lay eggs. Provide egg card for egg-laying. A female silkworm generally lays in an average of 400 eggs (ranges 300-500).
4. Sterilization of eggs: Collect and then sterilize the one-day-old eggs with 2% formalin for 5 minutes. Afterward, wash in running water.
5. Egg incubation: Leave the eggs at 22 to 26 degrees celsius temperature and 80 to 85% relative humidity in an incubator for incubation. To obtain uniform laying eggs at the blackhead stage are kept in black boxes on the day before hatching. In this way, the early maturing embryos are prevented from hatching, and the late-maturing embryo given time to develop and catch up with the early maturing ones. The next day, they are exposed to diffused light so that the larvae have uniformly responded to the phototrophic stimulus. By this method, hatching of 90% and over can be obtained in one day.
6. Larvae rearing
A. Brushing: The process of transferring the newly hatched silkworm to rearing trays is called brushing. During brushing, the cards with the newly hatched silkworm are placed in the rearing trays, and mulberry leaves cut into small squares (0.5 cm2) are sprinkled over the egg cards. The hatched silkworm crawled onto the tender leaves and started feeding. Later the cards are removed, and any worm still left on the cards is tapped on the rearing tray.
B. Feeding silkworm: Silkworms are feed to satisfy their apatite and ensure their healthy and uniform growth. Care should be taken to feed the silkworm a sufficient quantity of high-quality leaves. It is essential to supply chopped leaves to 1st and 2nd instar ones and whole leaves to the remaining instar. Usually, four feeding a day at six hours interval in practice. The quantity of the leaves required for rearing 50 layings or a box of 20,000 eggs at different instars is given below-
C. Bed cleaning: Removing the old mulberry leaves, faeces matter of silkworm, any dead or unhealthy silkworm etc., from the rearing bed is called bed cleaning. This is because the accumulation of any such matter creates environmental condition detrimental to the health of silkworm. Usually, the bed is cleaned once during the 1st instar, twice during the 2nd instar. i.e. just after the first mould and again before setting for the second mould and three times during the 3rd instar. i.e. just after the second mould in the middle of the age and again just before setting for the next mould.
During the 4th and 5th instar, the bed should be cleaned once a day in the morning. Nets are used usually for cleaning purposes. The net is spread over the bed, and one feeding is given before the nets are lifted and transferred to a fresh, clean tray. The worms crawl through the meshes in the net and come up to feed on the leaves on the nets. If the worm is healthy, mainly all the worm will come up, leaving the old leaves litter behind on the old trays, which are cleaned later. The mesh size of the net used for the different instar are as follows.
|1st and 2nd||2 mm2|
|4th and 5th||20 mm2|
D. Spacing: Provision of adequate rearing seat space is of great importance to silkworm’s vigorous and full growth. As the worm grows in weight and size. The density in the rearing bed increases and the condition of overcrowding are faced. It is, therefore, essential that the density of population in the rearing bed should be regulated. The spacing to be provided for different ages of the silkworm is given below.
|Age/Instar||No of larvae/ft2|
E. Environmental condition: Since silkworms have been reared in different countries, they are influenced by nature-wide delicate and susceptible to environmental condition. Among the various environmental factors that influence the silkworm, the most important are-
i. Temperature and humidity: The temperature and humidity requirement for different instars are given below-
|Age/Instar||Temperature (oc)||RH (%)|
ii. Photoperiod: The usual photoperiod for silkworm larvae is 12 hours. However, the light should not be too bright.
iii. Air: Silkworm required fresh air for their various physiological functions. So proper ventilation should be provided.
6. Ripening, spinning and cocoon formation
When the 5th instar larvae reach maturity, it can be understood by showing their translucent body colour and raising their head upwards. Maturity occurs within 6 to 7 days after the last mould, and in this time, they completely cease feeding. Pick the larvae in time and place them in Chandrika to facilitate undisturbed spinning cocoon formation.
7. Cocoon harvesting
Spinning taxes about 34 days and cocoon need to be harvested after full 5 days. 5 days are enough to transform a larva into pupa formation. The cocoon gets dry enough to stand well against the risk of being crushed during transport. Therefore, the cocoon should be harvested after 56 days and then dry immediately in an oven at 70-80 C for 24 hours or in the sun.
Diseases and pests of the silkworm moth
- Pebrine: Nosema bombycis (Protozoan).
- Uzi Fly: Exorista bobmycis.
- Dermestid beetles: Dermestes spp.
- Mites, Lizards, Rats, Squirrels, Birds, etc.
- Muscardine: Beauveria bassiana (Fungal).
- Flacherie: Bacillus bombysepticus (Bacterial).
- Earwigs: Euborellia annulipes.
- Grasseric: Virus.
- Gattine: Virus.
Pebrine Disease of the silkworm moth
Symptoms of Pebrine Disease
- Poor egg number.
- Reduction in size and weight.
- Lack of adherence of substratum, disuniform with more dead and unfertilized eggs.
- Irregular hatching.
- Loss of appetite, retarded growth and disuniformity in size.
- Irregular moulting.
- Heavy mortality after 2nd moult if infected at egg stage.
- Larvae shrink in size and vomit gut juice.
- Dark brown or black spots may be seen sometimes on the body.
- Pupa looks floppy and swollen.
- Irregular black spots on the body.
- Heavy mortality at the pupal stage.
- Improper development of moth.
- Deformed wings and distorted antennae.
- Poor mating and egg-laying.
- The scale of wings and abdominal area come off quickly.
Control Measures of Pebrine Disease
- Pebrine disease can be controlled by disinfecting the rearing room, equipment and rearing surroundings with 2% formalin.
- During rearing, unequal size worms and faecal matter should be microscopically examined for the presence of pebrine spores.
- If observed, larvae, cocoons and laying should be collected and burnt or buried.
- In the grainages, scientific methods of mother moth examination should be employed.
- Surface sterilization of the eggs with 2% formalin for 5 minutes.
Flacherie disease of the silkworm moth
Flacherie disease of the silkworm is caused by bacteria or virus individually or in the association. Depending on symptoms and cause, they are called bacterial flacherie disease, septicemia, sotto disease, etc. The disease may occur due to fluctuations in temperature, humidity, and feeding poor quality mulberry leaves.
Symptoms of Flacherie disease
- Larvae become sluggish and lose appetite.
- The body shrinks and becomes soft and flaccid.
- Growth is retarded, becomes dull and vomits gut juice.
- Loose clasping power of prolegs.
- Body ferments, turn to a different colour and oozes out a foul smell.
Control measures of Flacherie disease
- Raise only healthy and strong silkworm races.
- Maintain proper temperature
- (22-25°C) and humidity (80-85%) during incubation of eggs.
- Attend thorough disinfection of rearing room, appliances and surroundings.
- Take strict hygienic measures during rearing.
- Isolate infected larvae from the healthy one immediately and destroy by burning or dumping deep in the soil.
- Provide quality leaves for feeding and maintain proper spacing and ventilation.
- Maintain appropriate temperature and humidity during rearing.
- Destroy sluggish, irregular moulters and diseased worms.
- Do not allow late-stage worms to feed on tender, succulent leaves.
- Avoid injury to the worms, overcrowding of trays.
- Apply antibiotics like Streptomycin/Tetracyclin.
Grasserie disease of the silkworm moth
Grasserie is a viral disease in silkworm caused by Nuclear Polyhedrosis (NPV), Cytoplasmic polyhedrosis (CPV) and infectious flacherie. Nuclear polyhedrosis (NPV) is a major viral disease in silkworm. It is caused due to the presence of high temperature, high humidity and feeding of poor quality mulberry leaves. It is highly infectious.
Symptoms of Grasserie disease
In the early larval stage of infection, it is difficult to detect the disease. However, microscopic examination of larvae may indicate the presence of polyhedral bodies. As the disease advances, the larvae lose appetite, and skin becomes shiny before moulting. The intersegment membrane becomes swollen. The haemolymph or body fluid becomes turbid white. Microscopic examination shows the presence of a large number of polyhedral bodies.
Control measures of Grasserie disease
- Rear the larvae in clean and hygienic condition.
- Through disinfection of rearing room, appliances and surroundings.
- Ensure proper disinfection of the egg surface.
- Incubate eggs under hygienic conditions. Avoid touching with hands.
- Provide suitable and timely feed during rearing.
- Maintain proper spacing and adequate ventilation.
- Pick out diseased, weak and injured larvae and destroy them properly.
- Apply bed disinfectants as per recommended schedule and quantity.