As it is a elective paper for UG this Topic is related to types of Silkworms includes domestic and wild type silkworms - exotic and indigenous species. Hybrid races of silkworms to increase the quality and quantity of cocoon hence to increase the silk production. Life cycle of Bombyx mori. Structure of silk gland and secretion of silk.

1. D.VISHNU PRIYA
Assistant Professor
Department of Biotechnology
Bon secours college for women
SERICULTURE

2. TYPES OF SILKWORM

4. Indigenous Species
In India, indigenous silkworm races
includes univoltine, bivoltine and
multivoltine races.

5. Voltinism is a term used in biology to indicate the number of broods or generations of an
organism in a year. The term is most often applied to insects, and is particularly in use in
sericulture, where silkworm varieties vary in their voltinism.
● Univoltine (monovoltine) – referring to organisms having one brood or generation per
year
● Bivoltine (divoltine) – referring to organisms having two broods or generations per year
● Trivoltine – referring to organisms having three broods or generations per year
● Multivoltine (polyvoltine) – referring to organisms having more than two broods or
generations per year
● Semivoltine – There are two meanings:
● (biology) Less than univoltine; having a brood or generation less often than once per year
● or (adjective) referring to organisms whose generation time is more than one year.[1]

6. Exotic Species
Species that are found in an
environment that is generally not
local and has been introduced
from some other places.
Example : Bombyx mori
Native : China

7. Hybrid Races of Silkworms:
Sericulture farmers could soon see higher yields of silkworm cocoons, with the
Central Silk Board notifying some of the recently developed races of mulberry
(which feeds on mulberry leaves) and vanya (forest-based) silkworm eggs. These
races are now authorised for commercial production.
The newly developed hybrid of mulberry silkworm (PM x FC2) can produce 60 kg
of cocoons per 100 Disease Free Layings (silkworm eggs) and is said to be ‘better
than’ the earlier race titled PM x CSR. The tropical tasar silkworm (BDR-10) has
21% more productivity than the traditional Daba breed and the Eri silkworm (C2)
race is found to be ‘better’ than the local breed, according to industry experts. It can
produce 247 numbers of Eri cocoons per 100 DFLs, says a press release.

8. Morphology of Bombyx mori
Biology of Bombyx Mori:
● The mulberry silk moth, Bombyx mori belongs to the family Bombycidae. China is the
native place of this moth, but now it is totally domesticated and successfully reared in
India, Japan, Korea, Italy, France and Russia. In India 92% of country’s silk
production comes from mulberry moth.
● The worm or larva of this moth solely feeds on leaves of mulberry plant, so named as,
mulberry worm. Its wild ancestor B.mandarina still occurs in some isolated areas of
Himalaya’s foothill.

10. Hypothesis

12. Stage 1: Egg
An egg is the first stage of the life cycle of the silkworm. The egg is laid by a female moth which is mostly the size
of small dots. A female moth lays more than 350 eggs at a time. In the springtime, the eggs hatch due to the warmth
in the air. This procedure happens once in every year.
Stage 2: Silkworm
A hairy silkworm arises after the eggs crack. In this stage of silkworms, the growth happens. they feed on mulberry
leaves and consume a large amount of these leaves for around 30 days before going to the next stage.
Stage 3: Cocoon
In this stage, silkworms spin a protective cocoon around itself. It is the size of a small cotton ball and is made of a
single thread of silk.

13. Stage 4: Pupa
The pupa stage is a motionless stage. In this stage, people kill the pupa by plunging the cocoon into boiling water and unwind the silk thread.
Stage 5: Moth
In this stage, the pupa changes into an adult moth. The female moth lays eggs after mating and thus the life cycle of silkworm begins again.

16. The silk of silkworms is secreted by a pair of labial
gland, known as silk glands. The silk glands lie
ventral to the alimentary canal. In full grown
larvae, these occupy most of the body cavity. The
silk glands are tubular in shape with different
diameters in different regions. Each gland has 3
distinct regions

17. (1) Posterior Region:
Blunt, highly folded tubular posterior regions of both glands remain attached to tracheal bushes
of silkworm. This part secretes fibroin as fibrinogen which converted to fibroin upon extrusion.
(2) Middle region:
Most prominent and widest part of silk gland. It remains folded in a W-shaped structure and thus has
3 limbs — posterior, middle and anterior limbs. The posterior arm secretes sericin-I. It gets
surrounded by serecin-II secreted from the middle limb.
This sericin again gets surrounded by sericin- III secreted from the anterior limb. The middle region
of silk gland also acts as the reservoir of fibroin where the later gets mature during the storage period.
(3) Anterior region:
The thin anterior region of silk gland has no secretory role and only transports the assembled silk to
the spinneret.

18. Spinneret:
● It is a projection of the median part of the labium, which draws the silk out in the form of fine filament. The secreted
silk comes out as a thread or filament as it passes through silk press which resembles a typical salivary pump. The two
filaments coming out of two sides are called brins. The sericin (gum) layer of the two brins then bind together into a
single filament or bave.
Histologically the entire gland has 3 layers:
(1) The outer tunica propia with uniform thickness;
(2) The middle glandular layer with gland cells which increase in size during later instar stages of larval development and
(3) The inner tunica intima: It has varying thickness.
In the anterior region of the gland, this layer is very thick and is shed at each moult. In other regions of silk gland, it is thin
and not shed at each moult.
Filippi’s gland or Lyonnet’s gland:
● In the head region of the larvae, a pair of glands is situated which open into the anterior part of silk gland near its
opening into the spinneret. It is thought that these glands contribute some waxy materials to the silk thread or lubricate
the passage of silk while coming out.

19. Secretion of silk:
● The silk of silkworms is secreted by a pair of labial gland, known as silk glands. The
silk glands lie ventral to the alimentary canal. In full grown larvae, these occupy most of
the body cavity. The silk glands are tubular in shape with different diameters in different
regions.
● The larvae possess a pair of specially-modified salivary glands called silk glands.
These glands secrete a clear, viscous fluid that is forced through openings — called
spinnerets — on the mouthparts of the larva. The fluid hardens as it comes into contact
with air to become the silk thread.

20. Thank you