Bombyx mori
Encyclopedia
The silkworm is the larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

 or caterpillar
Caterpillar
Caterpillars are the larval form of members of the order Lepidoptera . They are mostly herbivorous in food habit, although some species are insectivorous. Caterpillars are voracious feeders and many of them are considered to be pests in agriculture...

 of the domesticated silkmoth, Bombyx mori (Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

: "silkworm of the mulberry
Mulberry
Morus is a genus of flowering plants in the family Moraceae. The 10–16 species of deciduous trees it contains are commonly known as Mulberries....

 tree"). It is an economically important insect, being a primary producer of silk
Silk
Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity...

. A silkworm's preferred food is white mulberry
White Mulberry
Morus alba, known as white mulberry, is a short-lived, fast-growing, small to medium sized mulberry tree, which grows to 10–20 m tall. The species is native to northern China, and is widely cultivated and naturalized elsewhere...

 leaves, but it may also eat the leaves of any other mulberry tree (i.e., Morus rubra or Morus nigra) as well as the Osage Orange. It is entirely dependent on humans for its reproduction and does not occur naturally in the wild. Sericulture
Sericulture
Sericulture, or silk farming, is the rearing of silkworms for the production of raw silk.Although there are several commercial species of silkworms, Bombyx mori is the most widely used and intensively studied. According to Confucian texts, the discovery of silk production by B...

, the practice of breeding silkworms for the production of raw silk, has been underway for at least 5,000 years in China, from where it spread to Korea
Korea
Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...

 and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, and later to India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

 and the West.

The silkworm was domesticated from the wild silkmoth Bombyx mandarina
Bombyx mandarina
Bombyx mandarina, the Wild Silkmoth, is an insect from the moth family Bombycidae. It is the closest relative of Bombyx mori the Domesticated Silkmoth or "silkworm" . Unlike the domesticated relative which is unable to fly or indeed persist outside human care, the Wild Silkmoth is a fairly ordinary...

which has a range from northern India to northern China, Korea, Japan and far the eastern regions of Russia. The domesticated silkworm derives from Chinese rather than Japanese or Korean stock. It is unlikely that silkworms were domestically bred before the Neolithic
Neolithic
The Neolithic Age, Era, or Period, or New Stone Age, was a period in the development of human technology, beginning about 9500 BC in some parts of the Middle East, and later in other parts of the world. It is traditionally considered as the last part of the Stone Age...

 age: it was not until then that the tools required to facilitate the manufacturing of larger quantities of silk thread had been developed. The domesticated B. mori and the wild B. mandarina
Bombyx mandarina
Bombyx mandarina, the Wild Silkmoth, is an insect from the moth family Bombycidae. It is the closest relative of Bombyx mori the Domesticated Silkmoth or "silkworm" . Unlike the domesticated relative which is unable to fly or indeed persist outside human care, the Wild Silkmoth is a fairly ordinary...

can still breed and sometimes produce hybrids.

The moth – the adult phase of the life cycle – cannot fly. Silkmoths have a wingspan of 3–5 cm (1.5–2 inches) and a white hairy body. Females are about two to three times bulkier than males (for they are carrying many eggs), but are similarly colored. Adult Bombycidae
Bombycidae
Bombycidae is a family of moths. The best-known species is Bombyx mori or silkworm, native to northern China and domesticated for millennia...

s have reduced mouth parts and do not feed, though a human caretaker can also feed them.

Process

Eggs take about fourteen days to hatch into larvae, which eat continuously. They have a preference for white mulberry
White Mulberry
Morus alba, known as white mulberry, is a short-lived, fast-growing, small to medium sized mulberry tree, which grows to 10–20 m tall. The species is native to northern China, and is widely cultivated and naturalized elsewhere...

, having an attraction to the mulberry oderant cis-jasmone. They are not monophagous since they can eat other species of Morus as well as some other Moraceae
Moraceae
Moraceae — often called the mulberry family or fig family — are a family of flowering plants comprising about 40 genera and over 1000 species. Most are widespread in tropical and subtropical regions, less so in temperate climates...

. Their droppings are black. Hatchlings and second-instar larvae are called kego and chawki in India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

. They are covered with tiny black hairs. When the color of their heads turns darker, it indicates that they are about to molt
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...

. After molting, the instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...

 phase of the silkworm emerges white, naked, and with little horns on the backs.

After they have molted four times (i.e., in the fifth instar phase), their bodies become slightly yellow and the skin become tighter. The larvae will then enter the pupa
Pupa
A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...

 phase of their life cycle and enclose themselves in a cocoon
Pupa
A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...

 made up of raw silk produced by the salivary glands. The cocoon provides a vital layer of protection during the vulnerable, almost motionless pupal state. Many other Lepidoptera
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...

 produce cocoons, but only a few—the Bombycidae
Bombycidae
Bombycidae is a family of moths. The best-known species is Bombyx mori or silkworm, native to northern China and domesticated for millennia...

, in particular the Bombyx
Bombyx
Bombyx is the genus of true silkmoths or mulberry silkmoths of the family Bombycidae. It traditionally contained two species as well as one natural hybrid and one human-dependent hybrid.-Species:* Bombyx horsfieldi...

 genus, and the Saturniidae
Saturniidae
The Saturniidae, commonly known as saturniids, are among the largest and most spectacular of the moths. They form a family of Lepidoptera, with an estimated 1,300 to 1,500 described species worldwide...

, in particular the Antheraea
Antheraea
Antheraea is a moth genus belonging to the family Saturniidae. Several species of this genus have caterpillars which produce wild silk of commercial importance...

 genus—have been exploited for fabric production.

If the animal is allowed to survive after spinning its cocoon and through the pupa phase of its life cycle, it will release proteolytic enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s to make a hole in the cocoon so that it can emerge as a moth. These enzymes are destructive to the silk and can cause the silk fibers to break down from over a mile in length to segments of random length, which ruins the silk threads
Yarn
Yarn is a long continuous length of interlocked fibres, suitable for use in the production of textiles, sewing, crocheting, knitting, weaving, embroidery and ropemaking. Thread is a type of yarn intended for sewing by hand or machine. Modern manufactured sewing threads may be finished with wax or...

. To prevent this, silkworm cocoons are boiled. The heat kills the silkworms and the water makes the cocoons easier to unravel. Often, the silkworm itself is eaten (see Cuisine).

Cocoon

The cocoon is made of a thread of raw silk from 300 to about 900 meters (1,000 to 3,000 feet) long. The fibers are very fine and lustrous, about 10 micrometers (1/2,500th of an inch) in diameter. About 2,000 to 3,000 cocoons are required to make a pound of silk. At least 70 million pounds of raw silk are produced each year, requiring nearly 10 billion pounds of mulberry leaves. The FAO estimates the world production of raw silk at 164971 tonnes in 2009 . According to E. L. Palmer, one pound of silk represents about 1,000 miles of filament. The annual world production represents 70 billion miles of silk filament. This silk is usually processed to remove natural waxes or gums such as the sericin, a water-soluble protective layer that solidifies immediately when exposed to air. It is sometimes subsequently dyed.

Research

Due to its miniature size and ease of culture, the silkworm has become a model organism
Model organism
A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to...

 in the study of Lepidopteran and arthropod biology. Fundamental findings on pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...

s, hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...

s, brain structures and physiology have been made with the silkworm. One example of this was the molecular identification of the first known pheromone, bombykol
Bombykol
Bombykol is a pheromone released by the female silkworm moth to attract mates. Discovered by Adolf Butenandt in 1959, it was the first pheromone to be characterized chemically...

 which required extracts from 500,000 individuals, due to the very small quantities of pheromone produced by any individual worm.

Currently, research is focusing on genetics of silkworms and the possibility of genetic engineering. Many hundreds of strains are maintained, and over 400 Mendelian mutation
Mendelian inheritance
Mendelian inheritance is a scientific description of how hereditary characteristics are passed from parent organisms to their offspring; it underlies much of genetics...

s have been described. Another source suggests 1000 inbred domesticated strains are kept worldwide. One useful development for the silk industry are silkworms that can feed on food other than mulberry leaves, including an artificial diet. Research on the genome also raises the possibility of genetically engineering silkworms to produce proteins, including pharmacological drugs, in the place of silk proteins.

The company Kraig Biocraft Laboratories
Kraig Biocraft Laboratories
Kraig Biocraft Laboratories, Inc. is a biotechnology company focused on the commercialization of new textiles and high performance fibers including spider silks. Kraig Biocraft Laboratories was founded in April 2006 to develop and commercialize spider silks and other high performance polymers using...


has used research from the Universities of Wyoming
University of Wyoming
The University of Wyoming is a land-grant university located in Laramie, Wyoming, situated on Wyoming's high Laramie Plains, at an elevation of 7,200 feet , between the Laramie and Snowy Range mountains. It is known as UW to people close to the university...

 and Notre Dame
University of Notre Dame
The University of Notre Dame du Lac is a Catholic research university located in Notre Dame, an unincorporated community north of the city of South Bend, in St. Joseph County, Indiana, United States...

 in a collaborative effort to create a silkworm that is genetically altered to produce spider silk. In September 2010 it was announced at a press conference at the University of Notre Dame that the effort had been successful.

In January 2010, National University of Singapore
National University of Singapore
The National University of Singapore is Singapore's oldest university. It is the largest university in the country in terms of student enrollment and curriculum offered....

 together with Republic Polytechnic
Republic Polytechnic
Republic Polytechnic , commonly abbreviated to RP, is a tertiary institution located in Singapore. It was the first school system in Singapore to use Problem-based learning pedagogy for all its diplomas....

 were in the process of creating "super" silk. The "super" silk are produced by coaxing "silkworms to spin stronger silk by exposing them (silkworms) to an electric field before they (silkworms) spin" . Silk produced through this new method is so strong as to be bullet-proof.

Domestication

The domesticated variety, compared to the wild form, has increased cocoon size, growth rate and efficiency of its digestion. It has also gained tolerance to human presence and handling and living in crowded conditions. It also cannot fly and lacks fear of potential predators. These changes have made it entirely dependent upon humans for survival.

Silkworm breeding:

The silkworm is one of the world's most genetically modified animals. Silkworms were first domesticated during the Han Dynasty in China about 2000 years ago. Since then, the silk production capacity of the species has increased nearly tenfold. Silkworm is one of the few organisms wherein the principles of genetics and breeding were applied to harvest maximum output. It is next only to maize in exploiting the principles of 'heterosis' and 'cross breeding'.
Silkworm breeding is aimed at the overall improvement of silkworm from a commercial point of view. The major objectives of silkworm breeding are improving fecundity, healthiness of larvae, quantity of cocoon and silk production, disease resistance, etc.
Fecundity refers to the egg laying capacity of a breed. It is a very important factor, since commercial sericulture is strongly dependent on silkworm egg availability.
Healthiness of larvae leads to a healthy cocoon crop. Healthiness is dependent on factors such as better pupation rate, less number of dead larvae in the mountage, shorter larval duration (the shorter the larval duration, the lesser the chances of infection) and bluish tinged fifth instar larvae (it is observed that bluish colored fifth instar larvae are healthier than the reddish brown ones).
Quantity of cocoon and silk produced is directly related to the pupation rate and larval weight. Healthier larvae have greater pupation rates and cocoon weights.
Quality of cocoon and silk depends on a number of factors including genetics.
Specific purposes apart from commercial purpose are given attention by advanced countries to breed development for specific purposes like sericin production, sex limited breeds, thin/thick filament production etc.
Disease resistance breeding is important, as the major reason for crop losses is pathogen infection. Efforts are being made to select breeds which are tolerant or resistant to various pathogens.
http://silkwormmori.blogspot.com/2008/08/silkworm-breeding-certain-fundamental.html

Silkworm Raising For Entertainment and School Science Project:
In the USA, teachers may sometimes introduce insect life cycle to their students by raising silkworms in the classroom as a science project. Students have a chance to observe complete life cycles of insect from egg stage to larvae, pupa, moth and eggs.

The silkworm has been raised for entertainment in China and South Africa. Children often pass on the eggs, creating a noncommercial population. The experience provides children with the opportunity to witness the lifecycle of silkworms.
The practice of raising silkworms by children as pets has, in the non-silkfarming country of South Africa, led to the development of extremely hardy landraces of silkworm. This is because they are invariably subjected to hardships not encountered by commercially-farmed members of the species. However, these worms, not being selectively bred as such, are probably inferior in silk production and may exhibit other undesirable traits.

Genome

The full genome of the silkworm was published in 2008 by the International Silkworm Genome Consortium.

The genome of the silkworm is mid-range with a genome size
Genome size
Genome size is the total amount of DNA contained within one copy of a single genome. It is typically measured in terms of mass in picograms or less frequently in Daltons or as the total number of nucleotide base pairs typically in megabases . One picogram equals 978 megabases...

 of ~432 Mb. It was published in 2008 by the International Silkworm Genome Consortium. A draft sequence was published in 2004.

High genetic variability has been found in domestic lines of silkworms, though this is less than that among wild silkmoths (~83%). This suggests a single event of domestication, and that it happened over a short period of time, with a large number of wild worms having been collected for domestication. Major questions, however, remain unanswered: “Whether this event was in a single location or in a short period of time in several locations cannot be deciphered from the data,” Research also has yet to identify the area in China where domestication arose.

Cuisine

Like many insect species, silkworm pupae are eaten in some cultures (see Entomophagy
Entomophagy
Entomophagy is the consumption of insects as food. Insects are eaten by many animals, but the term is generally used to refer to human consumption of insects; animals that eat insects are known as insectivores...

). This unusual food may go by the English phrase "ground cucumber."
  • In Korea
    Korea
    Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...

    , they are boiled and seasoned to make a popular snack food known as beondegi
    Beondegi
    Beondegi are a popular snack food in Korean cuisine. Literally meaning "chrysalis" or "pupa" in Korean, Beondegi are steamed or boiled silkworm pupae which are seasoned and eaten as a snack. Beondegi are often served by street vendors, as well as in restaurants and drinking establishments...

    .
  • In China
    China
    Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

    , street vendors sell roasted silkworm pupae.
  • In Vietnam
    Vietnam
    Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...

    , this is known as .
  • Silkworms have also been proposed for cultivation by astronauts as space food
    Space food
    Space food is food products, specially created and processed for consumption by astronauts in outer space. The food has specific requirements of providing balanced nutrition for the health of individuals working in space, while being easy and safe to store, prepare and consume in the machinery...

     on long-term missions.

Silkworm legends

In China, there is a legend that the discovery of the silkworm's silk was by an ancient empress Lei Zu, the wife of the Yellow Emperor
Yellow Emperor
The Yellow Emperor or Huangdi1 is a legendary Chinese sovereign and culture hero, included among the Three Sovereigns and Five Emperors. Tradition holds that he reigned from 2697–2597 or 2696–2598 BC...

 and the daughter of XiLing-Shi. She was drinking tea
Tea
Tea is an aromatic beverage prepared by adding cured leaves of the Camellia sinensis plant to hot water. The term also refers to the plant itself. After water, tea is the most widely consumed beverage in the world...

 under a tree when a silk cocoon fell into her tea. As she picked it out and started to wrap the silk thread around her finger, she slowly felt a warm sensation. When the silk ran out, she saw a small larva. In an instant, she realized that this caterpillar larva was the source of the silk. She taught this to the people and it became widespread. There are many more legends about the silkworm.

The Chinese guarded their knowledge of silk. It is said that about AD 550, Christian
Christian
A Christian is a person who adheres to Christianity, an Abrahamic, monotheistic religion based on the life and teachings of Jesus of Nazareth as recorded in the Canonical gospels and the letters of the New Testament...

 monks smuggled silkworms, in a hollow stick, out of China and sold the secret to the Byzantine Empire
Byzantine Empire
The Byzantine Empire was the Eastern Roman Empire during the periods of Late Antiquity and the Middle Ages, centred on the capital of Constantinople. Known simply as the Roman Empire or Romania to its inhabitants and neighbours, the Empire was the direct continuation of the Ancient Roman State...

.

Silkworm diseases

Nosema bombycis is a microsporidium that kills 100% of silkworms hatched from infected eggs. This disease can be carried over from worms to moths, then eggs and worms again. This microsporidium comes from the food that silkworms eat. If silkworms get this microsporidium in their worm stage, there are no visible symptoms. However, mother moths will pass the disease onto the eggs, and 100% of worms hatching from the diseased eggs will die in their worm stage. To prevent this disease, it is therefore extremely important to rule out all eggs from infected moths by checking the moth’s body fluid under a microscope.

Botrytis bassiana is a fungus that destroys the entire silkworm body. This fungus usually appears when silkworms are raised under cold conditions with high humidity. This disease is not passed on to the eggs from moths, as the infected silkworms cannot survive to the moth stage. This fungus can spread to other insects.

Grasserie: If grasserie is observed in chawkie stage, then the chawkie larvae must have been infected while hatching or during chawkie rearing. Infected eggs can be disinfected by cleaning their surface prior to hatching. Infections can occur as a result of improper hygiene in the chawkie rearing house. This disease develops faster in early instar rearing.

Pebrine
Pébrine
Pébrine is a disease of silkworms, which is caused by microsporidian parasites, mainly Nosema bombycis and to a lesser extent Variomorpha, Pleistophora and Thelophania species....

is a disease caused by a parasitic microsporidian, Nosema bombycis Nageli. Diseased larvae show slow growth, an undersized, pale and flaccid body, and poor appetite. Tiny black spots appear on larval integument. Additionally, dead larvae will remain rubbery and do not undergo putrefaction after death.

Traditional Chinese medicine

Silkworm is the source of the "stiff silkworm", which is made from dried 4th or 5th instar larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

e which have died of white muscardine disease. Its uses are to dispel flatulence
Flatulence
Flatulence is the expulsion through the rectum of a mixture of gases that are byproducts of the digestion process of mammals and other animals. The medical term for the mixture of gases is flatus, informally known as a fart, or simply gas...

, dissolve phlegm
Phlegm
Phlegm is a liquid secreted by the mucous membranes of mammalians. Its definition is limited to the mucus produced by the respiratory system, excluding that from the nasal passages, and particularly that which is expelled by coughing . Phlegm is in essence a water-based gel consisting of...

 and relieve spasm
Spasm
In medicine a spasm is a sudden, involuntary contraction of a muscle, a group of muscles, or a hollow organ, or a similarly sudden contraction of an orifice. It is sometimes accompanied by a sudden burst of pain, but is usually harmless and ceases after a few minutes...

s.

External links

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