Introduction
The
word silk comes from ancient English: sioloc, from ancient Greek: σηρικός,
Romanized: serikos, "silken", finally compare from Asian sources
Mandarin s ī "silk". Silk is a natural protein fiber that we get from
insects that can be woven into textiles. Silk protein fibers are composed
primarily of fibroin and are produced by insect larvae specific to cocoon
formation. The most well-known silk captive mulberry silkworm Bombyx is found
in Mori's larvae cocoon.
1st
Neolithic silk production in China. During the last half of the first
millennium BC, the Silk was confined to China until the Silk Road reached some
stage. China has maintained a virtual monopoly on silk production for thousands
of years. Not limited to clothing, silk was also used for many more
applications, including writing, and the color of the silk worn was an important
guide to social class during the Tang Dynasty. Silk cultivation spread to Japan
around 300 AD and during Byzantine time’s silkworm eggs were able to hatch and
silkworm farming was started.
Cultivation of Silk
Silk
moths lay their eggs mainly on prepared paper. The eggs hatch and the
caterpillars are fed high-quality mulberry leaves. After about 35 days and 4
hatchings, the caterpillars become 10,000 times heavier than the cubs and are
ready to start cutting a cocoon. A straw frame is placed on top of the
caterpillar tray and each caterpillar moves its head in a pattern and begins to
spin a cocoon. The two glands produce liquid silk and force it through the
opening of the head called spinnerets. Liquid silk is coated with sericin, a
water-soluble protective gum, and is strong in contact with air. Within 2-3
days, the caterpillar spins about a 1-mile filament and is completely enclosed in
a cocoon. Silk farmers heat the cocoons to kill them and turn some into insects
to breed the next generation of dry ones. The cut cocoons are boiled and the
silk fibers soaked in water hold the silk fibers together to form a cocoon. The
fibers are then unwrapped to form unbroken threads. Since the single thread is
very delicate and fragile for commercial use, a single thread of silk is made
anywhere from three to ten strands.
Which Insects produce Silk?
A.
Silkworms produce silk when undergoing larval to adult metamorphosis. These
include not only the pet bombyx mori but also a wide variety of insect species,
most of which are used commercially for silk.
B.
Raspy cricket produces silk to make nests.
C.
Honeybee and bumblebee larvae produce silk to strengthen the wax cells in which
they pupate.
D.
Bulldog ants spin cocoons to protect themselves during pupation.
E.
Weaver ants use silk to connect leaves together to make communal nests.
F.
Webspinners have silk glands on their front legs.
G.
Hornets
H.
Silverfish
I. Mayflies
J.
Thrips
K.
Leafhoppers produce silk nests under the leaves of the trees where they live to
protect them against predators.
L.
Beetles
M.
Lacewings
N.
Fleas
O.
Flies
P.
Midges
Q.
Caterpillars of many butterfly species use silk to create shelters or attach to
substrates for pupation.
R.
Parasitic wasps such as braconids use silk cocoons for pupation.
Diseases of silkworm and its prevention
There
are different kinds of diseases that are found in silkworms. Such as below-
A.
Beauveria bassiana/ Muscardine
Beauveria
bassiana is a fungus that grows naturally in soils around the world and acts as
a parasite of various arthropod species, causing white muscadine disease; It
belongs to the entomopathogenic fungus. This fungus destroys the entire
silkworm body. It generally appears when silkworms are holding in cool
conditions with high humidity. The disease is not passed from insects to eggs
because infected silkworms cannot survive in the insect stage. It can spread to
other insects.
Symptoms-
i.
The larvae lose appetite and become inactive.
ii.
The presence of moist spots on the skin.
iii.
The larvae vomit and become shiny.
iv.
After death, the larvae gradually harden and then mummification occurs which
results in the growth of gaseous mycelium and conidia on the body and the body
becomes shiny white.
Prevention-
i.
Disinfect the nursery, its surroundings, and equipment with the disinfectant.
ii.
Control mulberry insects in the mulberry garden.
iii.
Collect diseased larvae before mummification and dispose of them by burning
iv.
Avoid low temperatures and high humidity in the rearing room.
v.
Use a heater/stove to raise the temperature if necessary.
vi.
Control the humidity in the bed during the rainy season
vii.
Apply bed disinfectant, Vijetha, and Vijetha supplement / Ankush / prescribed
bed disinfectant according to schedule and amount.
B.
Grasserie
It
also is known as nuclear poly-hydrosis, milky disease, or hanging disease is
caused by infection with the Bombyx mori Nucleo poly-hydro virus. If it is
observed in the chawkie stage, then the chawkie larvae must have been infected
while hatching or during chawkie rearing. Infected eggs can be disinfected by
cleaning their surfaces before hatching. Infections may occur as a result of
improper hygiene in the chawkie rearing house. This disease develops faster in
early instar rearing.
Symptoms-
i.
The skin of the infected larva saw became brighter before it melted and failed
to molt.
ii.
Inter-segmental swelling occurs and body-color turns yellow.
iii.
Infected larvae move restlessly along the rim of the rearing bed/tray.
iv.
Infected larval bodies rupture easily and cloudy white hemolymph emerges.
Prevention-
i.
Make it a habit to completely disinfect the nursery, its surroundings, and any
recommended disinfectant equipment.
ii.
If a high incidence of the disease is observed in the previous crop, conduct
optional disinfection with 0.3% lime solution.
iii.
Practice personal and nurturing hygiene.
iv.
Collect diseased larvae and ensure their proper disposal.
v.
Maintain optimum temperature and humidity in the nursery.
vi
Feed quality mulberry leaves and avoid overcrowding.
vii.
Apply the recommended bed disinfectant according to schedule and amount.
viii
Feed Amrut as per schedule for grass root disease control.
C.
Pebrine
It
is a disease caused by a parasitic microsporidian, Nosema bombycis. Diseased
larvae show slow growth, undersized, pale, and flaccid bodies, and poor
appetite. Tiny black spots appear on the larval integument. Additionally, dead
larvae remain rubbery and do not undergo putrefaction after death.
Symptoms-
i.
Hatching irregular eggs of a silkworm.
ii.
Irregular body size and melting of larvae.
iii.
Infected larvae lose their appetite and become inactive on wrinkled skin.
iv.
Infected worms have black pepper spots on their bodies.
v.
When examined under a microscope with the presence of bright oval spores, white
pustules appear on the silk glands.
Prevention-
i.
Disinfect the nursery, neighborhood, and with the recommended disinfectant.
ii.
Strict mother moth testing and hand disinfection and disease-free layers of
silkworm eggs.
iii.
Adhere to strict hygiene rules during rearing.
iv.
Control mulberry insects in and around mulberry gardens.
v.
Apply the recommended bed disinfectant, Vijetha / Ankush according to the
schedule and quantity.
vi
Continue to monitor seed grains to eliminate microsporidian infections.
D.
Flacherie
Its
infected silkworms look weak and are colored dark brown before they die. The
disease destroys the larva's gut and is caused by viruses or poisonous food. Various
diseases caused by a variety of funguses are collectively named Muscardine.
Symptoms-
i.
The larvae become soft and shiny.
ii.
The growth of infected larvae is inhibited, becomes inactive, and vomits
intestinal juices. The stool becomes soft with more moisture.
iii.
Occasionally chain-type excretion and rectal protrusion are also observed.
iv.
The larvae's head and chest become transparent.
v.
Symptoms of toxicity such as paralysis and sudden death are observed when
Bacillus thuringiensis is infected. After death, the larvae turn black and give
off a foul odor.
vi
Sometimes, dead larvae turn red when infected by Serratia SP.
Prevention-
i.
Disinfect the nursery, its surroundings, and equipment with the germicides.
ii.
Pick up diseased larvae and burn them.
iii.
Provide good quality leaves growing under good sunlight and recommended inputs.
Do not provide mature / over-stored / dirty leaves for silkworms
iv.
Avoid starvation, overcrowding, and stool accumulation in the rearing bed.
v.
Rear silkworm under optimal temperature and humidity.
vi
Avoid larval injuries.
vii.
Apply the recommended bed disinfectant according to schedule and amount.
viii
Feed nectar according to schedule for control of the flaccid disease.
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