Silk Moth (Silk Worm)
Animal Husbandry of Class 12
Silk Moth (Silk Worm)
It belongs to Order-Lepidoptera, 3 genera : Bombyx, Antherea, Attacus produce different types of silk, live on different host plant. Larval stage produces silk.
Species Type of Silk Host Plant:
- Bombyx mori (reared) Mulberry silk Mulberry
- Antherea paphia (wild) Tassar silk Arjuna, Palas, Sal, Kusum
- Antherea assamensis (wild) Munga silk Champa, Oak (found in Assam)
- Attacus recini (reared) Eri silk Castor plant
- Antherea royali (wild) Tassar silk Oak tree
- Attacus atlas (the largest insect, found in Indonesia)
Life Cycle (Bombyx mori)
Adult are without mouth part and digestive system; male dies after fertilizing the female. Female lives for 3–4 days till laying of eggs. About 300–500 eggs are laid on the leaves of host plant, sticked by gluish secretion.
Larva (Caterpillar)
Is highly active and feeding stage 1.5mm larva hatches out within 5-7 days, starts feeding and growing. Feeding, locomotory and sensory organs are well developed. Undergoes 4-5 moulting within the period of 30-45 days. 5th instar larva is fully grown up (10-12cm) mature stage which stops feeding and settles at one place. Salivary gland modifies into silk gland which opens upon lower lip.
Secretion of Silk
Silk is secreted from silk glands which are extended from the 4th to 8th segments of the abdomen part of the body. Silk glands are actually modified salivary glands, when this pasty secretion comes in contact with air, it becomes hard and changes into strong and flexible silk fibres.
Silk is compoused of two types of proteins :
- Fibroin : Constitutes 75% of the silk thread.
- Secicin : Constitutes 25% of the silk thread.
Larva spins this thread around itself forming cocoon in 4-5 days, within it changes into pupa (chrysalis). Diapause (embryonic sleep) is the arrested development for a long time the pupa undergoes sometime.
Types of silk
Four types of silks are produced in India. These are mulberry silk (contributes about 91.7%), eri silk (contributes about 6.4%), tasar silk (contributes about 1.4%) and muga silk (contributes about 0.5%).
Procurement of silk
Before emergence of adult, cocoons are collected and treated with boiling water to isolate the thread. Thread is spun out on the reel and processed for making fabrics. One cocoon consists of 1000 - 2000 mtr of thread. For 450 gm of silk (i.e. for one saree) - 25,000 to 30,000 cocoons are required. Sericulture is the rearing of silk worm of commercial production of silk. The techniques were first developed in China and later smuggled to India, by a Chinese Princess married to an Indian King. China and Japan are the world leader in silk production with the facility of indoor culture. 3.5 crore tons of silk is produced in the world per annum.
Lac Insect
It belongs to order, Hemiptera the most common species is Lacifer lacca (earlier names ad Tachardia), As an ectoparasite it sucks juice of the host plant. The insect lives on trees such as Fig (Ficus bengalensis), Babool (Acacia, Zizyphus jujua), Palash (Butea frondosa), Sal (Shorea robusta), Kusum (Carthamus tinctorius). The differences between male and female insects are
Male Female
- Body with distinct head, thorax and abdomen – Body round with only rostral part distinct
- Wings, legs, antenna, eyes, well developed – All absent
- Motile form – Non-motile form
- Mouth parts and digestive system absent – Mouth part is piercing and sucking type
- Lives for only few days – Lives long
Life Cycle
After emergence male comes out of its chamber and enters female chamber, fertilizes the female Female lays 300–400 eggs within her chamber. Nymphs hatch out in a month or so, first moulting occurs within mother’s chamber 2nd instar nymphs swarm out of mother chamber and settle at new places on the tree. Starts sucking plant sap and grow, mature as male or female adults. During this period nymphs also secrete lac as their covering.
Inoculation or Infection
Before swarming 8-10 inch pieces of the branch having chambers are cut and tied to the branches of fresh trees. This way nymphs are shifted to other trees.Infection may be natural or artificial.
Two crops are procurred in a year : (1) Vasanti and (ii) Ranjini. Lac is secreted mainly by the adult female and some nymph from cutaneous gland to make its house on the tree twings. Contains Resin - 85%, water and other substances. Uses of lac for making sealing wax, shellac, varnish, paints, polishes, electric insulators, gramophone records, bangles, toys etc. Jharkhand is the largest producer of lac and India largest producer of lac in the world. Other use of the insect is for preparing coloring substance like alta, mahavar, etc from dried insect.
Other Beneficial Insects
Cochineal insects (Dactylopius coccus) Grows on cactus plant Dried powder of insect body is used to make dyes, alta, mahavar Blister beetle (Lytta) medicinal value, body extract is used to make cantheridine, widely used with hair oil.
