Silkworm breeding:
Pupa
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 coloured 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.
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 non-commercial 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-silk-farming 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 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.
