embryogenesis in silkworms

Embryogenesis ? ?

Developmental process that usually begins once the egg has been fertilized.

Why? To identify suitable stages for refrigeration.To know about initiation, continuation &

termination of diapause.Device strategies for long term cold storage.To identify when diapause terminates.

EMBRYOGENESIS

Fertilization

Sperm nucleus + egg nucleus (syngamy) = diploid zygote

( EMBRYO) – 2 hr@ 250 C

Cleavage

Nucleus divides mitotically to form many which lie in polar plasm

( meroblastic).

Germ band formation (24 hr)

Blastoderm cells in the ventral side of egg divides & collect to form lamelliform structure called ventral plate

Ventral plate further thickens to form germ band which later sink inside the egg – Daruma stage.

A membraneous layer forms two folds around the germ band called serosa (entire surface) & amnion

( ventral surface)

ORGANOGENESIS

Otsu –A stage:It is swelling of cephalic lobe

Otsu –B stage:It is distinct depression stage.

Hei - A stage: body becomes long & slendercephalic lobe is distinct1st 4 segments form head, next 3 segments form abdomen & last 11 segments form thorax

Hei - B stage:Development of cephalic embryo upto 80%

Period of shortening & organ formation

Embryo expands in girth & shortens , segmental

appendages develops distinctly.

Ectoderm forms fore gut & hind gut , endoderm forms

midgut.

Alimantary canal, head, thoracic legs , abdominal appendages are formed.

Eye spot stage (8th day)

Bristles grow around body surface

Dark pigmentation around mouth & head which can be

seen through egg shell as blue spot

Head pigmentation

Blastokinensis

It is an active movement of embryo from the ventral to the dorsal side of the egg and at the same time revolves

1800 on its long axis

Reference

Comprehensive sericulture - G .Ganga Introduction to sericulture - S.Ganga & J.Sulochana Chettyhttp://www.seriinfo.@10% html.http://www.seriuniv.comhttp://www.seriagro@20%.html