Draw and explain the life style of a silk worm
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Lifecycle of Silkworm (With Diagram)
Family: Bombycidae
Genus: Bombyx,
Species: B. mori
The Silkworm, Bombyx mori produces the silk of commercial importance. It is the caterpillar of a moth whose cocoon is used to make silk. This insect is also called the silkworm-moth and the mulberry silkworm (fig. 8.12). Male and female moths are flightless and lack functional mouth parts. The moths differ in morphological features. The female has a larger abdomen whereas the male has a much larger pair of antennae. A. Larvae feeding on mulberry leaves. B. Cocoon
Female moth laying eggsThe life cycle of Bombyx mori demonstrates the most advanced form of metamorphosis. The serial progressions of four distinct stages of development complete one generation of the species; egg (ova), larvae, pupa and imago.
Ova:
Egg is the first stage of a silkworm’s life cycle. The female moth lays an egg about the size of an ink dot during summer or the early fall. The egg remains in dormant stage until spring arrives. The warmth of the spring stimulates the egg to hatch. The egg of Bombyx mori is a very small and hard structure; about the size of a pin head and resembling a poppy seed (fig. 8.13). The egg shell provides a protective covering for embryonic development. When first laid, an egg light yellow. A fertile ovum darkens to a blue-gray within a few days.
Larva:
The larva is the vegetative stage where growth takes place. The larva of Bombyx mori, commonly called a silkworm, is host specific to mulberry. During growth, the larva molts 4 times. The period between successive molts is called an instar. The silk worm, upon hatching, is about 1/8th of an inch and extremely hairy.
Young silkworms can only feed on tender mulberry leaves. However, during the growth phase they can eat tougher mulberry leaves as well. The larval stage lasts for about 27 days and the silkworm goes through five growth stages called instars, during this time. During the first molting, the silkworm sheds all its hair and gains a smooth skin.
Pupa:
As the silkworm prepares to pupate, it spins a protective cocoon. About the size and color of a cotton ball, the cocoon is constructed from one continuous strand of silk, perhaps 1.5 km long (nearly a mile). The silk cocoon serves as protection for the pupa. Cocoons are shades of white, cream and yellow depending on silkworm genetics. After a final molt inside the cocoon, the larva develops into the brown, chitin covered structure called the pupa. Metamorphic changes of the pupa result in an emerging moth (fig. 8.14).