silk moth

Domesticated Silkmoth
Silkworm
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Paired male (above) and female (below)

Paired male (above) and female (below)
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Silkworm, 4th or 5th instar

Silkworm, 4th or 5th instar
Conservation status
Domesticated
Scientific classification
Kingdom:Animalia
Phylum:Arthropoda
Class:Insecta
Order:Lepidoptera
Family:Bombycidae
Genus:Bombyx
Species:B. mori
Binomial name
Bombyx mori
Linnaeus, 1758
Synonyms


Bombyx mori mori
The silkworm is the larva or caterpillar of Bombyx mori (Latin: "silkworm of the mulberry tree"), the domesticated silkmoth. A moth in the family Bombycidae, it is very important economically as the producer of silk. It is entirely dependent on humans for its reproduction and no longer occurs naturally in the wild. Silk culture has been practised for at least 5,000 years in China (Goldsmith et al. 2004). A silkworm's preferred food is White Mulberry leaves. It is native to northern China.

Its nearest wild relative is Bombyx mandarina which is able to hybridize with the domestic taxon (Goldsmith et al. 2004), and which ranges from northern India to northern China, Korea and Japan. It is not known when the domestic silkmoth diverged from its wild relatives, only that the domestic population originated from inland Chinese rather than Japanese or Korean stock (Maekawa et al. 1988, Arunkumar et al. 2006). Molecular clock studies suggesting an age of many millions of years cannot be taken seriously, as they assume that both species have evolved with constant speed since their divergence.

This is not correct however due to the domestication process having accelerated the pace of evolution (a similar problem affects the attempt to resolve the phylogeny of domestic Western honey bee subspecies). In fact, the domestic silkworm has undergone such strong artificial selection that it is completely unable to survive in the wild for any length of time. It is probably the most heavily domesticated animal known apart from domestic hybrids such as mules. Regardless whether the domestic silkworm is derived from a wild species that has since gone extinct, or from a stock of Bombyx mandarina that was taken into human care some 4,600 years ago (Yoshitake 1968), breeding of silkworms cannot have originated before the Neolithic as the tools necessary to make use of the silk thread on a large scale only have become available since then.

Sometimes, the Wild Silkmoth is considered a subspecies of Bombyx mori (the older specific name is used as per ICZN rules) as they are theoretically capable of full hybridization. However, due to the domesticated moth's requirement for human care to survive, gene flow is all but nonexistent and thus, despite its apparently recent origin, the domestic animal is generally treated as a distinct monotypic species today.

Development

Eggs take about ten days to hatch. Silkworms have a strong appetite, as do all lepidopteran larvae. They eat day and night, preferring White Mulberry but not being strictly monophagous they also take other species of Morus and some other Moraceae. Hatchlings and second-instar larvae are called kego (毛蚕, "hairy silkworm") in Japan, or chawki in India. They are covered with little black hairs. When the color of their heads turns darker, it means that it is time for them to molt. Later instars are white, nude, and have a horn on the back.

After they have moulted four times (i.e., in the fifth instar), their bodies turn slightly yellow and their skin becomes tighter. The larvae enclose themselves in a cocoon of raw silk produced in the salivary glands that provides protection during the vulnerable, almost motionless pupal state. Many other Lepidoptera produce cocoons, but only a few large Bombycidae and Saturniidae have been exploited for fabric production.

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Silkworm cocoons
Main article: Silk
The cocoon is made of a single continuous thread of raw silk from 300 to 900 meters (1000 to 3000 feet) long. The fibers are very fine and lustrous, about 10 micrometers (1/2500th of an inch) in diameter. About 2,000 to 3,000 cocoons are required to make a pound of silk. Based on 1 kilometer (about 1100 yards) per cocoon, ten unravelled cocoons could theoretically extend vertically to the height of Mt Everest. At least 70 million pounds of raw silk are produced each year, requiring nearly 10 billion pounds of mulberry leaves. According to E. L. Palmer (Fieldbook of Natural History 1949), one pound of silk represents about 1,000 miles of filament. The annual world production represents 70 billion miles of silk filament, a distance well over 300 round trips to the sun.

If the animal is allowed to survive after spinning its cocoon, it will release proteolytic enzymes to make a hole in the cocoon so that it can emerge as a moth. This would cut short the threads and ruin the silk. Instead, 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 also below).

The adult phase (the moth) cannot fly. The silkmoths have a wingspan of 3-5 cm (1.5 - 2 inches) and a white hairy body. Females have about twice to three times the bulk of males (for they are carrying many eggs), but are similarly coloured. Adults in the Bombycidae have reduced mouth parts and do not feed.




Females laying eggs

7-day (second instar) kego

Male adult. Scale is 15 mm

Female adult. Scale is 20 mm


Silkworm diseases

A number of commercially important diseases affect silkworms. Notable examples are:
  • Flacherie
  • Noninfectious or touffee flacherie, caused by exposure to excessive heat, particularly affects the fifth instar
  • Infectious or viral flaccherie is initially a virus infection. Caused by Bombyx mori infectious flacherie virus, Bombyx mori densovirus or Bombyx mori cypovirus 1, secondary infection by bacteria such as Serratia marcescens is common. A type of infectious flaccherie in which species of Streptococcus and Staphylococcus are the contributiong bacteria is known as thatte roga.
  • Polyhedral disease, polyhedrosis or grasserie, caused by Bombyx mori nuclear polyhedrosis virus (BmNPV, Baculoviridae)
  • Pébrine, caused by protozoans, usually Nosema bombycis and sometimes Variomorpha, Pleistophora and Thelophania species.
  • White muscardine disease, caused by the fungus Beauveria bassiana
  • Green muscardine disease, caused by the fungus Spicaria prasina
  • Aspergillosis, usually on already-sick larvae, caused by infection with the molds Aspergillus flavus or Aspergillus tamari.

Scientific and medical uses

Due to its large size and ease of culture, the silkworm has long been a model organism in the study of Lepidopteran and arthropod biology (Goldsmith et al. 2004). Fundamental findings on pheromones, hormones, brain structures and physiology were made with the silkworm (Grimaldi & Engel 2005). To characterize the first known pheromone, bombykol, extracts were needed from 500,000 individuals because only very small quantities are produced (Scoble 1995).

Currently, research is focusing on genetics of silkworms and genetic engineering. Many hundreds of strains are maintained, and over 400 Mendelian mutations have been described (Goldsmith et al. 2004). One useful mutant for the silk industry confers the ability to feed on food besides mulberry leaves, including an artificial diet (Goldsmith et al. 2004). The genome has been sequenced (Mita et al. 2004), and many projects have worked on genetic engineering of silkworms to produce desirable proteins in the place of silk. Such proteins include human drugs (Grimaldi & Engel 2005).

Silkworm is the source of the traditional Chinese medicine jiāngcán ("stiff silkworm", Simplified Chinese: 僵蚕; Traditional Chinese: 僵蠶, trade name "Bombyx batryticatus"). It is the dried body of the 4-5th instar larva which has died of the white muscardine disease. Its uses are to dispel flatulence, dissolve phlegm and relieve spasms.

Cuisine

Like many insect species, silkworm pupae are eaten in some cultures (see Entomophagy). In Korea they are boiled and seasoned to make a popular snack food known as beondegi. In China street vendors sell roasted silkworm pupae.

Silkworm legends

In China, there is a legend that the discovery of the silkworm's silk was by an ancient empress called Xi Ling-Shi (Chinese: 嫘祖; Pinyin: Léi Zǔ). She was drinking tea under a tree when a cocoon fell into her tea. She picked it out and as it started to wrap around her finger, she slowly felt a warm sensation. When the silk ran out, she saw a small cocoon. In an instant, she realized that this cocoon 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 a Chinese princess smuggled eggs to Japan, hidden in her hair. The Japanese thus began their love affair with silk. A single kimono requires the silk from 2100 silkworm moths to produce.

See also

References

  • Arunkumar, K.P.; Metta, Muralidhar & Nagaraju, J. (2006): Molecular phylogeny of silkmoths reveals the origin of domesticated silkmoth, Bombyx mori from Chinese Bombyx mandarina and paternal inheritance of Antheraea proylei mitochondrial DNA. Molecular Phylogenetics and Evolution 40(2): 419–427. doi:10.1016/j.ympev.2006.02.023 (HTML abstract). Supplementary figure 1 (JPG) Supplementary figure 2 (JPG) Supplementary figure 3 (JPG)
  • Goldsmith, Marian R.; Shimada, Toru & Abe, Hiroaki (2004): The genetics and genomics of the silkworm, Bombyx mori. Annu. Rev. Entomol. 50: 71-100. PMID 15355234. doi:10.1146/annurev.ento.50.071803.130456 (HTML abstract)
  • Grimaldi & Engel (2005): Evolution of the Insects. Cambridge University Press.
  • Maekawa, H.; Takada, N.; Mikitani, K.; Ogura, T.; Miyajima, N.; Fujiwara, H.; Kobayashi, M. & Ninaki, O. (1988): Nucleolus organizers in the wild silkworm Bombyx mandarina and the domesticated silkworm B. mori. Chromosoma 96: 263–269. doi:10.1007/BF00286912 (HTML abstract)
  • Mita, Kazuei; Kasahara, Masahiro; Sasaki, Shin; Nagayasu, Yukinobu; Yamada, Tomoyuki; Kanamori, Hiroyuki; Namiki, Nobukazu; Kitagawa, Masanari; Yamashita, Hidetoshi; Yasukochi, Yuji; Kadono-Okuda, Keiko; Yamamoto, Kimiko; Ajimura, Masahiro; Ravikumar, Gopalapillai; Shimomura, Michihiko; Nagamura, Yoshiaki; Shin-i, Tadasu; Abe, Hiroaki; Shimada, Toru; Morishita, Shinichi & Sasaki, Takuji (2004): The Genome Sequence of Silkworm, Bombyx mori. DNA Research 11(1): 27-35. PMID 15141943. doi:10.1093/dnares/11.1.27 PDF fulltext
  • Scoble, M.J. (1995): The Lepidoptera: Form, function and diversity. Princeton University Press.
  • Yoshitake, N. (1968): Phylogenetic aspects on the origin of Japanese race of the silkworm, Bombyx mori L.. Journal of Sericological Sciences of Japan 37: 83–87.

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The Silkworm (Bombyx mori) is the larva or caterpillar of a moth that is very important economically as the producer of silk.

Silkworm may also refer to:
  • Silkworm missile, a Chinese-built anti-ship cruise missile

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instar is a developmental stage of arthropods, such as insects, between each moult (ecdysis), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form.
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conservation status of a species is an indicator of the likelihood of that species continuing to survive either in the present day or the future. Many factors are taken into account when assessing the conservation status of a species: not simply the number remaining, but the
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Scientific classification or biological classification is a method by which biologists group and categorize species of organisms. Scientific classification also can be called scientific taxonomy, but should be distinguished from folk taxonomy, which lacks scientific basis.
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Arthropoda
Latreille, 1829

Subphyla and Classes
  • Subphylum Trilobitomorpha
  • Trilobita - trilobites (extinct)
  • Subphylum Chelicerata

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Insecta
Linnaeus, 1758

Orders
Subclass Apterygota
* Archaeognatha (bristletails)
* Thysanura (silverfish)
Subclass Pterygota
* Infraclass Paleoptera (Probably paraphyletic)

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Clipper Parthenos sylvia]]
The Clipper Parthenos sylvia


Scientific classification

Kingdom: Animalia

Phylum: Arthropoda
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Bombycidae

Bombycidae is a family of moths. The best-known species is Bombyx mori (Linnaeus) or silkworm, native to northern China and domesticated for millennia. Another well known species is Bombyx mandarina, also native to Asia.
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Bombyx
Linnaeus, 1758

Species

Bombyx mandarina
Bombyx mori

Bombyx is the genus of true silkmoths or mulberry silkmoths, moths of the family Bombycidae.
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binomial nomenclature is the formal system of naming species. The system is also called binominal nomenclature (particularly in zoological circles), binary nomenclature (particularly in botanical circles), or the binomial classification system.
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Carolus Linnaeus (Carl von Linné)

Carl von Linné, Alexander Roslin, 1775. Currently owned by and hanging at the Royal Swedish Academy of Sciences.
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Systema naturae was one of the major works of the Swedish doctor of medicine Carolus Linnaeus. Its full title is Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis
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In scientific nomenclature, synonyms are different scientific names used for a single taxon. Usage and terminology are different for zoology and botany.

Zoology

In zoological nomenclature, synonyms are different scientific names that pertain to the same taxon, for example
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larva (Latin; plural larvae) is a juvenile form of animal with indirect development, undergoing metamorphosis (for example, insects or amphibians).

The larva can look completely different from the adult form, for example, a caterpillar differs from a butterfly.
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caterpillar is the larval form of a member of the order Lepidoptera (the insect order comprising butterflies and moths). They are mostly phytophagous in food habit, with some species being entomophagous.
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Latin}}} 
Official status
Official language of: Vatican City
Used for official purposes, but not spoken in everyday speech
Regulated by: Opus Fundatum Latinitas
Roman Catholic Church
Language codes
ISO 639-1: la
ISO 639-2: lat
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moth is an insect closely related to the butterfly. Both are of the order Lepidoptera. The division of Lepidopterans into moths and butterflies is a popular taxonomy, not a scientific one.
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Bombycidae

Bombycidae is a family of moths. The best-known species is Bombyx mori (Linnaeus) or silkworm, native to northern China and domesticated for millennia. Another well known species is Bombyx mandarina, also native to Asia.
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Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from cocoons made by the larvae of the silkworm Bombyx mori reared in captivity (sericulture).
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M. alba

Binomial name
Morus alba
L.

The White Mulberry (Morus alba) is a short-lived, fast-growing, small to medium sized tree to 10–20 m tall, native to northern China, and widely
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China (Traditional Chinese:
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B. mandarina

Binomial name
Bombyx mandarina
Moore, 1872

Synonyms

Bombyx mori mandarina

Bombyx mandarina, the Wild Silkmoth
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A taxon (plural taxa), or taxonomic unit, is a name designating an organism or group of organisms. A taxon is assigned a rank and can be placed at a particular level in a systematic hierarchy reflecting evolutionary
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The molecular clock (based on the molecular clock hypothesis (MCH)) is a technique in genetics to date when two species diverged.
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phylogenetics (Greek: phyle = tribe, race and genetikos = relative to birth, from genesis = birth) is the study of evolutionary relatedness among various groups of organisms (e.g., species, populations).
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Artificial selection is the intentional breeding of certain traits, or combinations of traits, over others. It was originally defined by Charles Darwin in contrast to the process of natural selection, in which the differential reproduction of organisms with certain traits is
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Domestication refers to the process whereby a population of animals or plants becomes accustomed to human provision and control. Humans have brought these populations under their care for a wide range of reasons: to produce food or valuable commodities (such as wool, cotton, or
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