Embryological development in insect

Embryology is the branch of biology which deals with the growth and development of an embryo of
an organism, commencing with the union of male and female gametes.
Embryology includes the development of the fertilized egg and embryo and the growth of the organ
system.
Development of an insect from egg to adult can be divided into two parts
a.Early embryonic development - takes place inside the egg and
b. Post embryonic development – occurring outside the egg.

1. DIVISION OF ENTOMOLOGY TOPIC - EMBRYONIC DEVELOPMENT IN INSECT ENTO - 501 SUBMITTED TO: DR. DEVINDER SHARMA

2. CONTENTS Early Embryonic Development Post Embryonic Development

3. INTRODUCTION Embryology is the branch of biology which deals with the growth and development of an embryo of an organism, commencing with the union of male and female gametes. Embryology includes the development of the fertilized egg and embryo and the growth of the organ system. Embryonic Development In Insects: Development of an insect from egg to adult can be divided into two parts Early embryonic development - takes place inside the egg and Post embryonic development – occurring outside the egg.

4. Early Embryonic Development FERTILIZATION: The production of male (sperm) and female (ovum) gametes is commonly considered to be The First Phase in insect development. The union of gametes (spermatozoon and ovum) is The Second Phase of development, and creates a diploid zygote with the potential to form an entire organism and this process occurs through the fertilization of ovum with sperms. The sperm of most of insects remain alive for month to years within the Spermatheca . Fertilization occurs when the eggs are about to be laid and as each passes down the oviduct . The sperm enter into the eggs through Micropyle . Several sperms penetrate into the eggs and fertilization is affected by one of the sperms to form Zygote while the rest sperms degenerate.

5. Fertilization Of The Egg Fig: Fusion of sperm and egg nucleus Fig : Fertilized egg

6. INSECT EGGS The shapes and structural parts of an insect egg are as follows: Mature insect eggs are oval, elongate, may be spherical, disc or barrel like. The eggs are covered by two shells, a tough outer shell called the Chorion , and a thinner inner shell called The Vitelline Membrane . There is an opening called Micropyle at the chorion for the entrance of sperm. The two membranes surround a large nucleus and a mass of cytoplasm. The cytoplasm consists of a large central area of Yolk and a Peripheral Bounding Layer , the Periplasm , beneath the vitelline membrane. The egg nucleus lies in a central position and embedded in cytoplasm .

7. Fig : Different shapes of insect eggs Fig : Structural parts of an insect egg

8. Early Embryonic Development The early embryonic development is started immediately after fertilization of the eggs by sperms and it is occurred through a series of events that includes Cleavage Formation Of Blastoderm Vitellophages Formation Of Germband Gastrulation Formation Of Embryonic Membrane Blastokinesis Formation Of Organ System Appendages

9. Cleavage; is the repeated mitotic divisions of a fertilized ovum zygote. Formation of Blastoderm ; a one-cell-thick layer of cells surrounding the yolk.

10. Formation of Germ Band; the thickening of a Blastoderm forms a thin layer of cuboid cells subsequently they become columnar and thicker in the ventral region.

11. Gastrulation ; is the process by which the mesoderm and endoderm are invaginated within the ectoderm. The germ band becomes differentiated into a median area called middle plates and two lateral areas called lateral plates. The gastrulation stage begins when the mesoderm is formed from the middle in one of the three ways: by an invagination of the middle plates (Figure a), by growing lateral plates over middle plate (Figure b) or by proliferation of cells from the inner surface (Figure c).

12. Formation Of The Embryonic Membrane

13. BLASTOKINESIS; The embryo begins to move within the yolk, undergoing rotation, revolutions and marked displacement, the phenomenon is called blastokinesis .

14. DEVELOPMENT OF ORGAN SYSTEM From the three germ layer- ectoderm, mesoderm, and endoderm- the various organs and tissues of the insect develop. The ECTODERM gives rise to the body wall, tracheal system, nervous system, the malpighian tubles , foregut and hindgut; The MESODERM gives rise to the muscular system, heart and gonads; The ENDODERM gives rise to midgut .

15. DIFFERENT APPENDAGES OF INSECT EMBRYO

16. GENERAL SUMMARY OF INSECT EMBRYOGENESIS FROM FERTILIZATION TO COMPLETION OF ORGANOGENESIS.

17. Alternative Strategies of Acquiring Nutrients by Embryos VIVIPARITY Pseudoplacental Viviparity Adenotrophic Viviparity Hemocoelous Viviparity PARTHENOGENESIS Thelytoky Arrhenotoky POLYEMBRYONY PEDOGENESIS Endo Parasitic Hymenoptera Like Platygaster Cecidomyids . Ovoviviparity

18. Post Embryonic Development HATCHING: During the hatching process the young insect may chew its way through the Egg's Chorion or it may swell in size by imbibing air until the egg shell "cracks" along a predetermined line of weakness. Once the hatchling emerges, it is called a First Instar Nymph (Or Larva). As it grows, it will continue to develop and mature. These post-embryonic changes are known as Morphogenesis .

19. MORPHOGENESIS Once an insect hatches from the egg it is usually able to survive on its own, but it is small, wingless, and sexually immature. Its primary role in life is to eat and grow. If it survives, it will periodically outgrow and replace its exoskeleton (a process known as Molting ). Collectively, all changes that involve growth, molting, and maturation are known as Morphogenesis .  

20. MOLTING Step 1: Apolysis -- separation of old exoskeleton from epidermis Step 2: Secretion of inactive molting fluid by epidermis Step 3: Production of cuticulin layer for new exoskeleton Step 4: Activation of molting fluid Step 5: Digestion and absorption of old endocuticle Step 6: Epidermis secretes new procuticle Step 7: Ecdysis -- shedding the old exo- and epicuticle Step 8: Expansion of new integument Step 9: Tanning -- sclerotization of new exocuticle

21. Metamorphosis Each time an insect molts , it gets a little larger. It may also change physically in other ways -- depending on its type of metamorphosis: ametabola , hemimetabola , or holometabola .

22. mOST lARVAE cAN bE gROUPED iNTO oNE oF fIVE cATEGORIES bASED oN pHYSICAL aPPEARANCE : Larval Type Common Name Examples Campodeiform Scarabaeiform Vermiform Eruciform Elateriform Crawler White grub Maggot Caterpillar Wireworm Lady beetle, lacewing June beetle, dung beetle House fly, flesh fly Moths and butterflies Click beetle, Flour beetle

23. Pupae can be grouped into one of three categories based on physical appearance: Exarate Pupa Obtecta Pupa Coarctate Pupa Chrysalis Most Of The Coleoptera I.E. Beetles Lepidoptera (Moths) Cyclorrhapha Of Diptera (Housefly) Butterflies. Examples Are:

24. REFERENCES https://projects.ncsu.edu/cals/co ......... R.F.Chapman , The insect: structure and function, fourth edition, cambridge university press, U.K. Razzabali.webs.com……. https://www.scribd.com ...... Google search……

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