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Village Agriculture, Horticulture and Sericulture Assistant · Chapter 13

Sericulture: mulberry and silkworm rearing

What to remember

  • Sericulture is the rearing of silkworms to produce silk. It has three parts: growing the food plant (mulberry), rearing silkworms to get cocoons, and reeling cocoons into raw silk.
  • The mulberry silkworm Bombyx mori gives most of the world's silk. It is fed only on mulberry leaves and completes four moults and five instars in the larval stage.
  • Silkworm health depends on clean rearing houses, good leaf, correct temperature and humidity, and quick action against diseases such as pebrine, flacherie, grasserie and muscardine.

Types of silk

SilkSilkwormFood plant
Mulberry silkBombyx moriMulberry (Morus)
TasarAntheraea mylittaArjun, Asan and other forest trees
EriSamia riciniCastor and similar
MugaAntheraea assamensisSom and Soalu; golden silk of Assam

Mulberry silk is a domesticated silk, and tasar, eri and muga are wild or semi-wild silks (vanya silk). India is a major silk producer and also the only country producing all four types. The Central Silk Board (Bengaluru) works for the development of the industry, and State sericulture departments support farmers. Dharmavaram and other centres in Andhra Pradesh are known for silk sarees.

Silk is a protein fibre. It contains fibroin (the main protein, about 75%) and sericin (silk gum, about 25%) that is removed by degumming.

Mulberry cultivation

  • Species: Morus alba is the common one; improved varieties are V1, S36, Kanva-2 (M5) and others, chosen for high leaf yield and quality.
  • Climate and soil: warm climate with rainfall or irrigation, well-drained loamy soil, pH near neutral.
  • Propagation: by stem cuttings (about 6-8 inch long, with 3-4 buds) planted in rows. Spacing is commonly close, such as 90 cm × 90 cm, or narrow-row systems.
  • Manuring: heavy feeders; farmyard manure, nitrogen, phosphorus and potash in splits after each pruning.
  • Irrigation: needed at regular intervals; drip is used for water saving.
  • Pruning and harvest: bottom pruning or other pruning is done after each crop. Leaf is harvested by leaf picking (for young worms) or by cutting shoots (shoot harvest) for late age worms. Leaf of good quality is tender, green, with high moisture and protein.
  • Pests and diseases: leaf spot, powdery mildew, leaf rust and root rot; pests such as mealy bug, thrips and whitefly. The leaf of sprayed plants must not be fed before the waiting period of the chemical.

Silkworm life cycle and races

Life cycle: egg → larva → pupa → moth (adult) — complete metamorphosis.

  • Egg: laid by the moth, small, oval. Eggs are called layings and disease-free layings are sold as DFLs. Eggs are incubated at about 25°C and 80% humidity. Hatching is after about 9-10 days.
  • Larva: five instars with four moults. The larva eats the most in the fifth instar. Total larval period is about 24-28 days.
  • Pupa: formed inside the cocoon spun by the mature larva. The silk is from the salivary (silk) glands.
  • Moth: emerges after about 10-12 days; mating and egg laying follow. Moths do not feed.

Races by number of generations per year:

RaceGenerations per yearFeatures
UnivoltineOneEuropean origin; high silk quality, low hardiness
BivoltineTwoGood silk quality; need careful rearing
MultivoltineManyTropical, hardy, lower silk quality

Cross breeds (multivoltine × bivoltine) combine hardiness and yield, and are common in South India.

Rearing practice

  • Disinfection: wash the rearing house and equipment and disinfect with bleaching powder (about 5% solution) or formalin (about 2%) before rearing. Keep a footbath at the entrance.
  • Chawki rearing: rearing of young worms (first two instars up to the second moult) in a clean central place, with tender leaf at high humidity (about 85-90%) and temperature around 27-28°C. Chawki worms are then given to farmers.
  • Late-age rearing (third to fifth instar): lower humidity (about 70-75%), temperature 24-26°C, plenty of ventilation, wide spacing and thick leaf; use a rearing stand or shoot rearing.
  • Bed cleaning: remove litter and dead worms regularly; apply lime or a disinfectant dust.
  • Moulting: worms stop feeding before moulting. Do not feed until most have moulted.
  • Mounting: when mature worms stop feeding and look shiny and translucent, they are placed on mountages (such as bamboo trays or plastic collapsible mountages) to spin cocoons.
  • Harvest of cocoons: after about 5-6 days of spinning. Remove flimsy and defective cocoons.
  • Stifling: killing the pupa by hot air or steam so that the moth does not cut the cocoon; then the cocoons are dried.
  • Reeling: unwinding the continuous silk filament from cocoons in warm water on a reeling machine (cottage basin, charka or multi-end reeling). Many filaments are twisted to form raw silk. A cocoon filament may be several hundred metres long.

Diseases and pests of silkworm

DiseaseCauseNotes
PebrineProtozoan Nosema bombycis (microsporidian)Passed through eggs; moths are examined under microscope; most serious
FlacherieBacteria and virusesDull, flaccid larva, foul smell; due to poor leaf and high humidity
Grasserie (jaundice)Nuclear polyhedrosis virusSkin swells and bursts with milky fluid; seen before moulting or mounting
MuscardineFungus, such as Beauveria bassianaLarva becomes hard and covered with white powder

Pest: uzi fly (Exorista bombycis) lays eggs on larvae and maggot comes out of the cocoon. Dermestid beetles and ants attack stored cocoons or reared worms. Control: hygiene, disinfection, DFLs, net on windows, and removal of diseased worms to be burnt or buried.

Quality, units and worked examples

  • Shell ratio = (cocoon shell weight ÷ whole cocoon weight) × 100. If a cocoon weighs 2.0 g and its shell 0.44 g, shell ratio = 22%.
  • Renditta = weight of cocoons needed for 1 kg of raw silk. If 9 kg of cocoons give 1 kg silk, renditta = 9. A lower value is better.
  • Reeling recovery % = (raw silk weight ÷ cocoon weight) × 100; 1 kg silk from 8 kg cocoons = 12.5%.
  • Egg hatching % = (hatched eggs ÷ total eggs) × 100; 450 hatched from 500 = 90%.
  • Larval survival = 450 mature larvae out of 500 hatched = 90%.
  • Leaf need grows with age; fifth instar eats about four-fifths of the total leaf, so leaf supply must be planned.
  • Mulberry gardens produce leaf in several crops per year in tropical areas. Sericulture is a labour-intensive, rural income activity that suits small farmers and women.

Silkworm management details

Leaf quality and feeding: young worms need tender, nutritious leaf from the top of the shoot, finely chopped, while grown worms accept coarse leaf. Feed three to four times a day at fixed times. Overfeeding leaves wet litter, and underfeeding leaves worms weak. Wilted or sprayed leaf must not be fed. Leaf is stored in a cool, damp room covered with a wet cloth.

Environment control: temperature and humidity change with the stage of the worm. Cold and hot days are managed with ventilation, shade over the house, and charcoal heaters or humidifiers where needed. Proper spacing of beds avoids crowding; crowding causes disease spread and uneven growth.

Spinning and harvest: a mature worm turns pale, shrinks a little, stops eating and raises its head to look for a place to spin. One cocoon is spun from one continuous filament over about two to three days, and the pupa forms inside. Hygiene of the mounting area is important because dead worms rot and stain the cocoons. Good cocoons are firm and uniform; stained, double (two worms) or thin-shelled cocoons are separated.

Silk quality after reeling: raw silk is graded by evenness, cleanliness and strength (the denier is the unit of fineness, the weight in grams of 9,000 metres of silk). The twisted, finished silk is woven in sarees and fabrics; Andhra Pradesh has many handloom weaving clusters. Waste silk from broken cocoons is spun into spun silk.

Exam traps

  • Pebrine is a protozoan disease; grasserie is viral; muscardine is fungal; flacherie is bacterial/viral.
  • Chawki is young-age rearing, not the cocoon stage.
  • Fibroin is the silk protein; sericin is the gum.
  • Four moults make five instars.
  • Eri silk is from castor; tasar from Antheraea mylitta; muga from Assam.
  • DFL means disease free layings, not dead feed leaf.
  • Stifling kills pupa; reeling unwinds silk.
  • Multivoltine is hardy but gives lower silk quality; bivoltine gives better quality.

One-liners

  • Bombyx mori is the mulberry silkworm.
  • Mulberry is the food plant of Bombyx mori.
  • Larval stage has five instars.
  • Silk glands are modified salivary glands.
  • Pebrine is caused by Nosema bombycis.
  • Uzi fly is Exorista bombycis.
  • Muga silk comes from Assam.
  • Fibroin makes up most of silk.
  • Eggs of silkworm are called layings.
  • Central Silk Board is based in Bengaluru.
  • Mounting is placing mature worms to spin.
  • Cocoons are stifled before reeling.

Practice questions

  1. The scientific name of the mulberry silkworm is

    1. Samia ricini
    2. Antheraea mylitta
    3. Antheraea assamensis
    4. Bombyx mori
    Answer

    D. Bombyx mori

    Bombyx mori is the domesticated mulberry silkworm.

  2. Muga silk, known for its golden colour, is a speciality of

    1. Gujarat
    2. Punjab
    3. Karnataka
    4. Assam
    Answer

    D. Assam

    Muga silk comes from Antheraea assamensis of Assam.

  3. Eri silkworm is mainly fed on the leaves of

    1. Castor
    2. Neem
    3. Arjun
    4. Mulberry
    Answer

    A. Castor

    Eri silkworm (Samia ricini) feeds on castor.

  4. Tasar silk is produced by

    1. Bombyx mori
    2. Samia ricini
    3. Antheraea mylitta
    4. Philosamia only
    Answer

    C. Antheraea mylitta

    Antheraea mylitta is the tropical tasar silkworm.

  5. The larval stage of Bombyx mori has how many instars?

    1. Three
    2. Five
    3. Six
    4. Four
    Answer

    B. Five

    Larva passes through five instars separated by four moults.

  6. How many moults does the mulberry silkworm larva undergo?

    1. Six
    2. Three
    3. Five
    4. Four
    Answer

    D. Four

    Four moults make five instars.

  7. Pebrine disease of silkworm is caused by

    1. Exorista bombycis
    2. Nosema bombycis
    3. Nuclear polyhedrosis virus
    4. Beauveria bassiana
    Answer

    B. Nosema bombycis

    Pebrine is a protozoan (microsporidian) disease passed through eggs.

  8. Grasserie disease of silkworm is caused by

    1. A nuclear polyhedrosis virus
    2. A protozoan
    3. A fungus
    4. A mite
    Answer

    A. A nuclear polyhedrosis virus

    Grasserie (jaundice) is viral.

  9. White muscardine disease of silkworm is caused by a

    1. Virus
    2. Fungus
    3. Mite
    4. Protozoan
    Answer

    B. Fungus

    Beauveria bassiana is the fungus of white muscardine.

  10. The uzi fly that parasitises silkworm larvae is

    1. Exorista bombycis
    2. Musca domestica
    3. Nosema bombycis
    4. Bombyx mori
    Answer

    A. Exorista bombycis

    Uzi fly maggots feed inside the larva and bore out of the cocoon.

  11. The main protein of the silk filament is

    1. Sericin
    2. Collagen
    3. Fibroin
    4. Keratin
    Answer

    C. Fibroin

    Fibroin forms the core; sericin is the gum.

  12. The gummy protein that coats the silk filament is

    1. Fibroin
    2. Chitin
    3. Casein
    4. Sericin
    Answer

    D. Sericin

    Sericin is removed by degumming.

  13. DFL in sericulture stands for

    1. Double fibre layers
    2. Dead feed larvae
    3. Disease free layings
    4. Dried fresh leaves
    Answer

    C. Disease free layings

    DFLs are eggs certified free from disease, sold to farmers.

  14. Chawki rearing refers to the rearing of

    1. Pupae inside cocoons
    2. Young silkworms of the first two instars
    3. Moths for egg laying
    4. Mature worms before spinning
    Answer

    B. Young silkworms of the first two instars

    Chawki worms are reared in a clean central place up to the second moult.

  15. Stifling of cocoons is done to

    1. Disinfect the mulberry
    2. Wind the filament
    3. Soften the sericin
    4. Kill the pupa inside
    Answer

    D. Kill the pupa inside

    Stifling prevents the moth from piercing the cocoon.

  16. The silk glands of the silkworm are modified

    1. Salivary glands
    2. Fat body cells
    3. Mandibles
    4. Malpighian tubules
    Answer

    A. Salivary glands

    Silk is secreted by labial (salivary) glands of the larva.

  17. Mulberry is usually propagated by

    1. Stem cuttings
    2. Bulbs
    3. Leaf cuttings
    4. Tubers
    Answer

    A. Stem cuttings

    Stem cuttings with buds are planted for mulberry gardens.

  18. A univoltine race of silkworm produces

    1. Two generations per year
    2. Many generations per year
    3. One generation per year
    4. No eggs
    Answer

    C. One generation per year

    Univoltine means one brood per year.

  19. Mounting in silkworm rearing is

    1. Hatching of eggs
    2. Placing ripe worms on mountages to spin cocoons
    3. Cutting leaf shoots
    4. Spraying mulberry with nutrients
    Answer

    B. Placing ripe worms on mountages to spin cocoons

    Ripe worms are mounted so that they can spin.

  20. The Central Silk Board has its headquarters at

    1. Guwahati
    2. Hyderabad
    3. Chennai
    4. Bengaluru
    Answer

    D. Bengaluru

    CSB is headquartered in Bengaluru.

  21. A cocoon weighs 2.0 g and its shell weighs 0.44 g. The shell ratio is

    1. 22%
    2. 18%
    3. 4.4%
    4. 44%
    Answer

    A. 22%

    0.44 / 2.0 x 100 = 22%.

  22. 45 kg of cocoons give 5 kg of raw silk. The renditta is

    1. 5
    2. 225
    3. 9
    4. 40
    Answer

    C. 9

    Renditta = 45 / 5 = 9 kg cocoons per kg of silk.

  23. 1 kg of raw silk is reeled from 8 kg of cocoons. The reeling recovery is

    1. 80%
    2. 12.5%
    3. 8%
    4. 15%
    Answer

    B. 12.5%

    1 / 8 x 100 = 12.5%.

  24. Out of 500 eggs, 450 hatch. The hatching percentage is

    1. 45%
    2. 95%
    3. 50%
    4. 90%
    Answer

    D. 90%

    450 / 500 x 100 = 90%.

  25. 4800 eggs hatch out of 6000 laid. The hatching percentage is

    1. 88%
    2. 60%
    3. 80%
    4. 75%
    Answer

    C. 80%

    4800 / 6000 x 100 = 80%.

  26. 380 of 400 hatched larvae form cocoons. The survival is

    1. 95%
    2. 90%
    3. 85%
    4. 38%
    Answer

    A. 95%

    380 / 400 x 100 = 95%.

  27. The fifth instar eats about four-fifths of the total leaf. If a batch needs 500 kg of leaf, the fifth instar needs

    1. 250 kg
    2. 400 kg
    3. 300 kg
    4. 100 kg
    Answer

    B. 400 kg

    4/5 of 500 = 400 kg.

  28. Mulberry is planted at 90 cm x 90 cm. The number of plants per hectare is about

    1. 11,111
    2. 10,000
    3. 9,000
    4. 12,345
    Answer

    D. 12,345

    Area per plant 0.81 m2; 10,000 / 0.81 = 12,345.

  29. Mulberry planted 1 m x 0.5 m gives how many plants per hectare?

    1. 20,000
    2. 5,000
    3. 15,000
    4. 10,000
    Answer

    A. 20,000

    10,000 / 0.5 = 20,000.

  30. To make 100 litres of 2% formalin solution, the amount of formalin needed is

    1. 0.2 litre
    2. 5 litres
    3. 20 litres
    4. 2 litres
    Answer

    D. 2 litres

    2% of 100 L = 2 L.

  31. To prepare 20 litres of 5% bleaching powder solution (weight by volume), bleaching powder needed is

    1. 5 kg
    2. 100 g
    3. 1 kg
    4. 2 kg
    Answer

    C. 1 kg

    5% = 50 g per litre; 50 x 20 = 1000 g.

  32. If renditta is 8, the raw silk from 100 kg of cocoons is

    1. 80 kg
    2. 12.5 kg
    3. 800 kg
    4. 8 kg
    Answer

    B. 12.5 kg

    100 / 8 = 12.5 kg.

  33. A cocoon weighs 1.8 g and its shell weighs 0.36 g. The shell ratio is

    1. 10%
    2. 20%
    3. 18%
    4. 36%
    Answer

    B. 20%

    0.36 / 1.8 x 100 = 20%.

  34. Consider the statements. Which of the statements is/are correct? 1. Bombyx mori feeds on mulberry leaf 2. The larval stage has five instars

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are correct.

  35. Consider the statements. Which of the statements is/are correct? 1. Pebrine is a protozoan disease 2. Grasserie is a fungal disease

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Grasserie is viral.

  36. Consider the statements. Which of the statements is/are correct? 1. Fibroin is the silk gum 2. Sericin is removed in degumming

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    Sericin is the gum; fibroin is the fibre protein.

  37. Consider the statements. Which of the statements is/are correct? 1. Chawki rearing means rearing mature worms 2. Stifling is unwinding silk from the cocoon

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    D. Neither 1 nor 2

    Chawki is for young worms; stifling kills the pupa.

  38. Consider the statements. Which of the statements is/are correct? 1. Multivoltine races are hardy 2. Bivoltine races give many generations a year

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Bivoltine means two generations.

  39. Consider the statements. Which of the statements is/are correct? 1. Eri silk is obtained from castor-fed worms 2. Tasar is a wild silk

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are correct.

  40. Consider the statements. Which of the statements is/are correct? 1. Uzi fly is a predator of mulberry leaf 2. Uzi fly maggots emerge from the silkworm and damage the cocoon

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    It is a parasite of the larva.

  41. Consider the statements. Which of the statements is/are correct? 1. Silkworm moths feed on mulberry leaf 2. Cocoons are harvested before spinning is complete

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    D. Neither 1 nor 2

    Moths do not feed; cocoons are harvested after spinning.

  42. Consider the statements. Which of the statements is/are correct? 1. Mulberry is propagated by stem cuttings 2. Mulberry is raised from tubers

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    A. 1 only

    Mulberry is not tuber propagated.

  43. Consider the statements. Which of the statements is/are correct? 1. Late-age worms need lower humidity than chawki worms 2. Cocoons are harvested about 5-6 days after spinning starts

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are correct.

  44. Consider the statements. Which of the statements is/are correct? 1. Univoltine race gives many generations a year 2. Multivoltine is a tropical race

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    B. 2 only

    Univoltine gives one generation.

  45. Consider the statements. Which of the statements is/are correct? 1. Rearing houses are disinfected with bleaching powder or formalin 2. Silkworm eggs are incubated near 25 degrees C

    1. 1 only
    2. 2 only
    3. Both 1 and 2
    4. Neither 1 nor 2
    Answer

    C. Both 1 and 2

    Both are standard practice.

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