Bombyx mori | |
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Paired male (above) and female (below) | |
Fifth instar | |
Domesticated | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | Insecta |
Order: | Lepidoptera |
Family: | Bombycidae |
Genus: | Bombyx |
Species: | B. mori |
Binomial name | |
Bombyx mori | |
Synonyms | |
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Bombyx mori, commonly known as the domestic silk moth, is a moth species belonging to the family Bombycidae. It is the closest relative of Bombyx mandarina , the wild silk moth. Silkworms are the larvae of silk moths. The silkworm is of particular economic value, being a primary producer of silk. The silkworm's preferred food are the leaves of white mulberry, though they may eat other species of mulberry, and even leaves of other plants like the Osage orange. Domestic silk moths are entirely dependent on humans for reproduction, as a result of millennia of selective breeding. Wild silk moths, which are other species of Bombyx, are not as commercially viable in the production of silk.
Sericulture, the practice of breeding silkworms for the production of raw silk, has existed for at least 5,000 years in China, [1] whence it spread to India, Korea, Nepal, Japan, and then the West. The conventional process of sericulture kills the silkworm in the pupal stage. [2] The domestic silk moth was domesticated from the wild silk moth Bombyx mandarina , which has a range from northern India to northern China, Korea, Japan, and the far eastern regions of Russia. The domestic silk moth derives from Chinese rather than Japanese or Korean stock. [3] [4]
Silk moths were unlikely to have been domestically bred before the Neolithic period. Before then, the tools to manufacture quantities of silk thread had not been developed. The domesticated Bombyx mori and the wild Bombyx mandarina can still breed and sometimes produce hybrids. [5] : 342 It is unknown if B. mori can hybridize with other Bombyx species. Compared to most members in the genus Bombyx, domestic silk moths have lost their coloration as well as their ability to fly. [6]
Mulberry silkworms can be divided into three major categories based on seasonal brood frequency. Univoltine silkworms produce only one brood a season, and they are generally found in and around Europe. Univoltine eggs must hibernate through the winter, ultimately cross-fertilizing in spring. Bivoltine varieties are normally found in East Asia, and their accelerated breeding process is made possible by slightly warmer climates. In addition, there are polyvoltine silkworms found only in the tropics. Their eggs typically hatch within 9 to 12 days, meaning there can be up to eight generations of larvae throughout the year. [7]
Eggs take about 14 days to hatch into larvae, which eat continuously. They have a preference for white mulberry, having an attraction to the mulberry odorant cis-jasmone. They are not monophagous, since they can eat other species of Morus , as well as some other Moraceae, mostly Osage orange. They are covered with tiny black hairs. When the color of their heads turns darker, it indicates they are about to molt. After molting, the larval phase of the silkworms emerge white, naked, and with little horns on their backs.
After they have molted four times, their bodies become slightly yellow, and the skin becomes tighter. The larvae then prepare to enter the pupal phase of their life cycle, and enclose themselves in a cocoon made up of raw silk produced by the salivary glands. The final molt from larva to pupa takes place within the cocoon, which provides a layer of protection during the vulnerable, almost motionless pupal state. Many other Lepidoptera produce cocoons, but only a few — the Bombycidae, in particular the genus Bombyx, and the Saturniidae, in particular the genus Antheraea — have been exploited for fabric production.
The cocoon is made of a thread of raw silk from 300 to about 900 metres (980 to about 3,000 ft) long. The fibers are fine and lustrous, about 10 μm (0.0004 in) in diameter. About 2,000 to 3,000 cocoons are required to make one pound (0.45 kg). At least 70 million lb (32 million kg) of raw silk are produced each year, requiring nearly 10 billion cocoons. [8] [ better source needed ]
If the animal survives through the pupal phase of its life cycle, it releases proteolytic enzymes to make a hole in the cocoon so it can emerge as an adult 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 reduces the value of the silk threads, although these damaged silk cocoons are still used as "stuffing" available in China and elsewhere in the production of duvets, jackets, and other purposes. To prevent this, silkworm cocoons are boiled in water. The heat kills the silkworms, and the water makes the cocoons easier to unravel. Often, the silkworm is eaten.
As the process of harvesting the silk from the cocoon kills the pupa, sericulture has been criticized by animal welfare and rights activists. Mahatma Gandhi was critical of silk production based on the ahimsa philosophy "not to hurt any living thing". This led to Gandhi's promotion of cotton spinning machines, an example of which can be seen at the Gandhi Institute, [9] and an extension of this principle has led to the modern production practice known as Ahimsa silk, which is wild silk (from wild and semiwild silk moths) made from the cocoons of moths that are allowed to emerge before the silk is harvested.
The moth is the adult phase of the silk worm's life cycle. Silk moths have a wingspan of 3–5 cm (1.2–2.0 in) and a white, hairy body. Females are about two to three times bulkier than males (due to carrying many eggs). All adult Bombycidae moths have reduced mouthparts and do not feed.
The wings of the silk moth develop from larval imaginal disks. [10] The moth is not capable of functional flight, in contrast to the wild B. mandarina and other Bombyx species, whose males fly to meet females. Some may emerge with the ability to lift off and stay airborne, but sustained flight cannot be achieved as their bodies are too big and heavy for their small wings.
The legs of the silk moth develop from the silkworm's larval (thoracic) legs. Developmental genes like Distalless and extradenticle have been used to mark leg development. In addition, removing specific segments of the thoracic legs at different ages of the larva resulted in the adult silk moth not developing the corresponding adult leg segments. [10]
Due to its small size and ease of culture, the silkworm has become a model organism in the study of lepidopteran and general arthropod biology. Fundamental findings on genetics, pheromones, hormones, brain structures, and physiology have been made with the silkworm. [11] [ citation needed ] One example of this was the molecular identification of the first known pheromone, bombykol, which required extracts from 500,000 individuals, due to the small quantities of pheromone produced by any individual silkworm.[ citation needed ]
Many research works have focused on the genetics of silkworms and the possibility of genetic engineering. Many hundreds of strains are maintained, and over 400 Mendelian mutations have been described. [12] Another source suggests 1,000 inbred domesticated strains are kept worldwide. [13] One useful development for the silk industry is silkworms that can feed on food other than mulberry leaves, including an artificial diet. [12] Research on the genome also raises the possibility of genetically engineering silkworms to produce proteins, including pharmacological drugs, in the place of silk proteins. Bombyx mori females are also one of the few organisms with homologous chromosomes held together only by the synaptonemal complex (and not crossovers) during meiosis. [14] In the oocytes of B. mori, meiosis is completely achiasmate (lacking crossovers). [15] Even though synaptonemal complexes are formed during the pachytene stage of meiosis in B. mori, crossing-over homologous recombination does not occur between the paired chromosomes. [16]
Kraig Biocraft Laboratories [17] has used research from the Universities of Wyoming and Notre Dame in a collaborative effort to create a silkworm that is genetically altered to produce spider silk. In September 2010, the effort was announced as successful. [18]
Researchers at Tufts developed scaffolds made of spongy silk that feel and look similar to human tissue. They are implanted during reconstructive surgery to support or restructure damaged ligaments, tendons, and other tissue. They also created implants made of silk and drug compounds which can be implanted under the skin for steady and gradual time release of medications. [19]
Researchers at the MIT Media Lab experimented with silkworms to see what they would weave when left on surfaces with different curvatures. They found that on particularly straight webs of lines, the silkworms would connect neighboring lines with silk, weaving directly onto the given shape. Using this knowledge they built a silk pavilion with 6,500 silkworms over a number of days.
Silkworms have been used in antibiotic discovery, as they have several advantageous traits compared to other invertebrate models. [20] Antibiotics such as lysocin E, [21] a non-ribosomal peptide synthesized by Lysobacter sp. RH2180-5 [22] and GPI0363 [23] are among the notable antibiotics discovered using silkworms. In addition, antibiotics with appropriate pharmacokinetic parameters were selected that correlated with therapeutic activity in the silkworm infection model. [24]
Silkworms have also been used for the identification of novel virulence factors of pathogenic microorganisms. A first large-scale screening using transposon mutant library of Staphylococcus aureus USA300 strain was performed which identified 8 new genes with roles in full virulence of S. aureus. [25] Another study by the same team of researchers revealed, for the first time, the role of YjbH in virulence and oxidative stress tolerance in vivo. [26]
The domestic species B. mori, compared to the wild species (e.g., B. mandarina), has increased cocoon size, body size, growth rate, and efficiency of its digestion. It has gained tolerance to human presence and handling, and also to living in crowded conditions. The domestic silk moths cannot fly, so the males need human assistance in finding a mate, and it lacks fear of potential predators. The native color pigments have also been lost, so the domestic silk moths are leucistic, since camouflage is not useful when they only live in captivity. These changes have made B. mori entirely dependent upon humans for survival, and it does not exist in the wild. [27] The eggs are kept in incubators to aid in their hatching.
Silkworms were first domesticated in China more than 5,000 years ago. [28] [29]
Silkworm breeding is aimed at the overall improvement of silkworms from a commercial point of view. The major objectives are improving fecundity, the health of larvae, quantity of cocoon and silk production, and disease resistance. Healthy larvae lead to a healthy cocoon crop. Health is dependent on factors such as better pupation rate, fewer dead larvae in the mountage, [30] shorter larval duration (this lessens the chance of infection) and bluish-tinged fifth-instar larvae (which are healthier than the reddish-brown ones). Quantity of cocoon and silk produced are 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.
In the U.S., teachers may sometimes introduce the insect life cycle to their students by raising domestic silk moths in the classroom as a science project. Students have a chance to observe complete life cycles of insects from eggs to larvae to pupae to moths.
The domestic silk moth has been raised as a hobby in countries such as China, South Africa, Zimbabwe, and Iran. Children often pass on the eggs to the next generation, creating a non-commercial population. The experience provides children with the opportunity to witness the life cycle of silk moths.
The full genome of the domestic silk moth was published in 2008 by the International Silkworm Genome Consortium. [13] Draft sequences were published in 2004. [31] [32]
The genome of the domestic silk moth is mid-range with a genome size around 432 million base pairs. A notable feature is that 43.6% of the genome are repetitive sequences, most of which are transposable elements. At least 3,000 silkworm genes are unique, and have no homologous equivalents in other genomes. The silkworm's ability to produce large amounts of silk correlates with the presence of specific tRNA clusters, as well as some clustered sericin genes. Additionally, the silkworm's ability to consume toxic mulberry leaves is linked to specialized sucrase genes, which appear to have been acquired from bacterial genes. [13]
In 2018, Illumina's short reads for 137 strain genomes were published. [33] In 2022, Nanopore's long reads for 545 strain genomes were published. [34]
Silk moth pupae are edible insects and are eaten in some cultures:
Silkworms have also been proposed for cultivation by astronauts as space food on long-term missions. [37]
In China, a legend indicates the discovery of the silkworm's silk was by an ancient empress named Leizu, the wife of the Yellow Emperor, also known as Xi Lingshi. She was drinking tea 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 this caterpillar larva was the source of the silk. She taught this to the people and it became widespread. Many more legends about the silkworm are told.
The Chinese guarded their knowledge of silk, but, according to one story, a Chinese princess given in marriage to a Khotan prince brought to the oasis the secret of silk manufacture, "hiding silkworms in her hair as part of her dowry", probably in the first half of the first century AD. [38] About AD 550, Christian monks are said to have smuggled silkworms hidden in a hollow stick out of China, selling the secret to the eastern Romans.
According to a Vietnamese folk tale, silkworms were originally a beautiful housemaid running away from her gruesome masters and living in the mountain, where she was protected by the mountain god. One day, a lecherous god from the heaven came down to Earth to seduce women. When he saw her, he tried to rape her but she was able to escape and was hidden by the mountain god. The lecherous god then tried to find and capture her by setting a net trap around the mountain. With the blessing of Guanyin, the girl was able to safely swallow that net into her stomach. Finally, the evil god summons his fellow thunder and rain gods to attack and burn away her clothes, forcing her to hide in a cave. Naked and cold, she spit out the net and used it as a blanket to sleep. The girl died in her sleep, and as she wished to continue to help other people, her soul turned into silkworms.[ citation needed ]
Bombyx mori is essentially monophagous, exclusively eating mulberry leaves (Morus spp.). By developing techniques for using artificial diets, the amino acids needed for development are known. [39] The various amino acids can be classified into five categories:
Silk is a natural protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is most commonly produced by certain insect larvae to form cocoons. The best-known silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity (sericulture). The shimmering appearance of silk is due to the triangular prism-like structure of the silk fibre, which allows silk cloth to refract incoming light at different angles, thus producing different colors.
Morus, a genus of flowering plants in the family Moraceae, consists of 19 species of deciduous trees commonly known as mulberries, growing wild and under cultivation in many temperate world regions. Generally, the genus has 64 subordinate taxa, though the three most common are referred to as white, red, and black, originating from the color of their dormant buds and not necessarily the fruit color, with numerous cultivars and some taxa currently unchecked and awaiting taxonomic scrutiny. M. alba is native to South Asia, but is widely distributed across Europe, Southern Africa, South America, and North America. M. alba is also the species most preferred by the silkworm, and is regarded as an invasive species in Brazil and the United States.
Saturniidae, members of which are commonly named the saturniids, is a family of Lepidoptera with an estimated 2,300 described species. The family contains some of the largest species of moths in the world. Notable members include the emperor moths, royal moths, and giant silk moths.
Sericulture, or silk farming, is the cultivation of silkworms to produce silk. Although there are several commercial species of silkworms, the caterpillar of the domestic silkmoth is the most widely used and intensively studied silkworm. This species of silkmoth is no longer found in the wild as they have been modified through selective breeding, rendering most flightless and without defense against predators. Silk is believed to have first been produced in China as early as the Neolithic period. Sericulture has become an important cottage industry in countries such as Brazil, China, France, India, Italy, Japan, Korea, Russia, and Thailand. Today, China and India are the two main producers, with more than 60% of the world's annual production.
Bombykol is a pheromone released by the female silkworm moth to attract mates. It is also the sex pheromone in the wild silk moth. Discovered by Adolf Butenandt in 1959, it was the first pheromone to be characterized chemically.
Bombyx is the genus of true silk moths or mulberry silk moths of the family Bombycidae, also known as silkworms, which are the larvae or caterpillars of silk moths. The genus was erected as a subgenus by Carl Linnaeus in his 10th edition of Systema Naturae (1758).
Samia cynthia, the ailanthus silkmoth, is a saturniid moth, used to produce silk fabric but not as domesticated as the silkworm, Bombyx mori. The moth has very large wings of 113–125 mm (4.4–4.9 in), with a quarter-moon shaped spot on both the upper and lower wings, whitish and yellow stripes and brown background. There are eyespots on the outer forewings. The species was first described by Dru Drury in 1773.
Bombyx mandarina, the wild silk moth, is a species of moth in the family Bombycidae. It is the closest relative of Bombyx mori, the domesticated silk moth. The silkworm is the larva or caterpillar of a silk moth. Unlike the domesticated relative which is unable to fly or indeed persist outside human care, the wild silk moth is a fairly ordinary lepidopteran. Its main difference from the domesticated taxon is the more slender body with well-developed wings in males, and the dull greyish-brown colour.
The production of silk originated in Neolithic China within the Yangshao culture. Though it would later reach other places in the world, the art of silk production remained confined to China until the Silk Road opened at 114 BC. Even after trade opened, China maintained a virtual monopoly over silk production for another thousand years. The use of silk within China was not confined to clothing alone, and silk was used for a number of applications, such as writing. Within clothing, the color of silk worn also held social importance, and formed an important guide of social class during the Tang dynasty of China.
Thai silk is produced from the cocoons of Thai silkworms. Thailand's silkworm farmers cultivate both types of the domesticated silkworms that produce commercial silk: Samia ricini, commonly known as the eri silkworm, which produces matte eri silk, and the Bombyx mori, producer of the better known, glossy mulberry silk. The latter is by far the larger silk producer of the two.
China is the world's largest and earliest silk producer. The vast majority of Chinese silk originates from the mulberry silkworms. During the larval stage of its life cycle, the insects feed on the leaves of mulberry trees. Non-mulberry silkworm cocoon production in China primarily focuses on wild silk from the Chinese Tussah moth. This moth typically feeds on trees and its larvae spin coarser, flatter, yellower filament than the mulberry silkworms.
Wild silks have been known and used in many countries from early times, although the scale of production is far smaller than that from cultivated silkworms. Silk cocoons and nests often resemble paper or cloth, and their use has arisen independently in many societies.
Eri silk is a type of peace silk produced by the domesticated silkworm Samia ricini. It is primarily produced in the northeastern Indian states of Assam, Nagaland and Meghalaya, but it is also found in Bihar, Odisha, West Bengal and Andhra Pradesh on a smaller scale. It was imported to Thailand in 1974.
Antheraea pernyi, the Chinese oak tussar moth, Chinese tasar moth, or temperate tussar moth, is a large moth in the family Saturniidae. The species was first described by Félix Édouard Guérin-Méneville in 1855. Antheraea roylei is an extremely close relative, and the present species might actually have evolved from ancestral A. roylei by chromosome rearrangement.
The Bombyx hybrid is a hybrid between a male Bombyx mandarina moth and a female Bombyx mori moth. They produce larvae called silkworms, like all species of Bombyx. The larvae look a lot like the other variations. They are brown in the first half and gray at the bottom half, but they get larger black spots than other variations. Generally, they look like a normal Bombyx moth, but a bit darker. Hybrids are not used for silk, but for research. Because Bombyx mori males lost their ability to fly, their females are much more likely to mate with a male Bombyx mandarina. The reverse is possible, but both species have to be kept in the same container. Since Bombyx hybrids are much more common than the other variation, more is known about them.
Bombyx huttoni, or the chocolate-tipped silk moth, is a moth belonging to the silk moth family, Bombycidae. It is closely related to the domestic silk moth.
Antheraea paphia, known as the South India small tussore, the tasar silkworm and vanya silkworm is a species of moth of the family Saturniidae found in India and Sri Lanka. The bulk of the literature on this species uses a junior synonym, Antheraea mylitta, rather than the correct name, A. paphia. It is one of a number of tasar silkworms, species that produce Tussar silk, a kind of wild silk that is made from the products of saturniid silkworms instead of the domesticated silkworm.
Commercial butterfly breeding or captive butterfly breeding is the practice of breeding butterflies and moths in controlled environments to supply the stock to research facilities, universities, zoos, insectariums, elementary and secondary schools, butterfly exhibits, conservation organizations, nature centers, individuals, and other commercial facilities. Some butterfly and moth breeders limit their market to wholesale customers while other breeders supply smaller volumes of stock as a retail activity. Some small scale and larger scale breeders limit their businesses to the provision of butterflies or moths for schools. Others provide butterflies to be used and released in commemorative events. The release usually occurs in the natural range of the butterfly.
Ahimsa silk, also known as peace silk is a method of nonviolent silk breeding and harvesting. Wild silk moths are bred rather than the domestic variety. It allows the completion of the metamorphosis of the silkworm to its moth stage, whereas most silk harvesting requires the silkworms to be killed in their cocoon stage. No animals suffer or die for the silk to be produced, making it a favorable alternative to normal silk for those who object to harming animals.
Borocera cajani, also known as landibe in Malagasy, is a species of silk-producing lasiocampid moth endemic to Madagascar. It is often confused with the similar Borocera madagascariensis, which has the same Malagasy name. However, B. cajani is the species associated with silk production in highland Madagascar, while B. madagascariensis is found in the coastal portion of the island.
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