webinar on embryonic, organogenesis and post embryonic developments in insects with descriptive images and brief points relevant to the topic.

2. Guidance By
Dr. K. D. Shah
Assistant Professor
Department of Entomology
JAU, Junagadh
Prepared By
Varshini .K. T.
1 M.Sc. (Agri.)
Department of Entomology
JAU, Junagadh
College of Agriculture
JAU, Junagadh

3. INTRODUCTION
Ø Embryogenesis is the process by which a single egg develops into
a multicellular individual.
Ø embryonic development in insects begin when the gametes
produced by females(oocytes) fuse with gametes produced from
males (sperm) through the process of fertilization to form a zygote.
Ø The zygote then divides mitotically to produce all different cells
that comprise the body of nymph (exopterygote /hemimetabolous
species) or larva (endopterygote/holometabolous species),which
will hatch from egg

4. Ø Embryogenesis proceeds through similar series of steps in most
of the insect species, but there are also a number of variations
that in some cases are associated with unique life histories.
Ø Broadly embryogenesis can be divided into two categories.
Early embryonic development –events taking place inside the
egg
Post embryonic development – events taking place after
hatching from egg.

5. THE EGG
Ø First stage of development in all oviparous insects is egg. it is the
inconspicuous, inexpensive and inactive stage .
Ø It contains nucleus, cytoplasm, yolk (protein, lipids and
carbohydrates) surrounding these components is the egg shell
vitelline membrane(innermost)
EGG SHELL wax layer
chorion (outermost)

6. Ø Primary constituents of chorion are proteins that undergo hardening
process either before or shortly after oviposition .
Ø Hardening is due to peroxidase –catalyzed protein cross linking
Ø In some species chorion is sub divided into two anatomically
distinct layers called endochorion and exochorion
Ø Endochorion is a homogeneous electron dense layer ,while the
exochorion consists of a fibrilar network.
Ø There is an opening called micropyle at the chorion for the entrance
of sperm

7. TYPES OF EGGS
1.Sculptured eggs - Castor butterfly
2.Elongate eggs - Sorghum shootfly
3.Rounded eggs - Citrus butterfly
4.Nits - Head louse
5.Egg with float - Anopheles mosquito
6.Pedicellate eggs - Green lace wing
7.Barrel shaped eggs - Stink bug
8.Ootheca - Cockroach
9.Egg raft - Culex mosquitoes

8. EARLY EMBRYONIC DEVELOPMENT
§ Fertilization and zygote
formation
§ Cleavage
§ Formation of blastoderm
§ Formation of vitellophages
§ Formation of germband
§ Gastrulation
§ Formation of embryonic
membrane
§ Blastokinesis
§ Formation of appendages
§ Formation of organ system
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

9. FERTILIZATION AND ZYGOTE FORMATION
Ø Sperm released from the spermatheca of the females pass through the
micropyle
Ø Usually egg nucleus is diploid until the entry of sperm stimulates
meiotic division leading to the formation of one egg nucleus and three
polar bodies (which are eventually reabsorbed into the yolk)
oogonium
Polar body
spermatocyte
Egg nucleus
sperms
Ø The haploid female nucleus usually migrates toward the centre of the egg and
unites with the sperm nucleus , forming zygote

10. CLEAVAGE
Ø Cleavage is the repeated mitotic divisions of a fertilized ovum zygote.
Ø Zygotic divisions produce large numbers of nuclei lacking cell
membranes but each surrounded by a small island of cytoplasm is
called an energid.

11. FORMATION OF BLASTODERM
Ø The energids move and migrate towards the periphery (periplasm) of
the egg and arrange in a layer of circle within the yolk.
Ø The energids may undergo further, one or more mitotic divisions and
retain the distinct cell walls and subsequently form a layer of cells,
called the blastoderm.
Ø The blastoderm, in true sense, is the primary germinal epithelium. It
lies just beneath the vitelline membrane.

12. FORMATION OF BLASTODERM

13. FORMATION OF VITELLOPHAGES
Ø All energids do not migrate to the periphery to form the
blastoderm some of them lie behind within the yolk are called the
yolk cells, merocytes or vitellophages.
Ø Vitellophages digest (liquify) the yolk and make nutrients
available to the developing embryo and also may form a part of
the midgut epithelium

14. FORMATION OF GERM BAND
Ø Initially blastoderm forms a thin layer of
cuboid cells all over the yolk. Subsequently,
they become thicker in the ventral region of
the egg and become columnar.
Ø This thickening is called embryonic
primordia or germ band which develops
future embryo. The rest blastoderm
remains as extra-embryonic membrane
called serosa.

15. ØBased on initial size ,germ bands can be of three types
1.Short germ band - Come from panoistic ovaries.
Contain large yolk with relatively little cytoplasm.
Development is slow.
Eg : Orthoptera and Odonata
2.Long germ band - Come from meroistic ovaries
Contain large amount of cytoplasm with little yolk
Development is rapid
Eg :Lepidoptera,Coleoptera,Diptera&Hymenoptera
3.Intermediate band - Segmentation in thorax occurs rapidly but the
abdominal portion of germband grows slowly and
segmentation is slow

16. GASTRULATION
• During gastrulation , a part of the germ band sinks unto the ball
of blastodermal cells and germ layers are formed that will give
rise to different organs and tissues .
• Germ layers include an outer layer (ectoderm) an inner layer
(endoderm) and a middle layer (mesoderm)
• 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.

17. By an invagination of the
middle plates
eg :Clytra
i
The gastrulation stage begins when the mesoderm is formed from
the middle one in one of the three ways
By growing lateral plates
over middle plate
eg: Apis
iii

18. Ø Cells proliferation from each end of the mesoderm (derived from
middle plate) and eventually grow around the yolk. These represent
the beginning of the endoderm (derived from vitellophages), and they
form the lining of what will be the future mid gut of the insect.
By proliferation of cells
from the inner surface
eg: Locusta
iii

19. FORMATION OF THE EMBRYONIC MEMBRANE
Ø The germ band becomes covered by one or more embryonic
membranes. Soon after formation of germ band, the serosa from
either side extend until both extensions meet and fuse in the ventral
mid line.
Ø Small cavity forms on the ventral surface of the germ band called
amniotic cavity.
Ø The amniotic cavity is bound by a membrane is called amnion.

21. BLASTOKINESIS
• The embryo begins to move within the yolk, undergoing rotation,
revolutions and marked displacement, the phenomenon is called
blastokinesis.
• The movements taking place from the posterior to anterior pole of egg
are termed as the anatrepsis (ana- upward)
• Whereas those from ventral to dorsal surface of the egg are called
katatrepsis

22. anterior
posterior
dorsalvental

23. Ø The consequence of these extensive movements is that the
embryo reverses its position relative to the yolk i.e., after
blastokinesis , the yolk gets enclosed within the embryo.
Ø Various degrees of these movements occur in different insects .
Only Lepidoptera undergo marked blastokinetic movements
among Holometabola

24. Diagramatic representation consequence of blastokinesis

25. FORMATION OF APPENDAGES
• With the differentiation of germ layers, the germ band begins the
process of metamerism.
• The first division appears between the future labial and the first
thoracic segments, dividing the embryo into broad head region called
protocephalon and a long narrow posterior trunk, the protocorm.
• Soon after the prethoracic as well as thoracic segmentation
commences so that 3 segmented thoracic region is differentiated
from the long unsegmented protocorm – protopod phase
• The unsegmented protocorm represents the abdomen.

26. • Polypod stage:- segmentation of abdomen and appendage formation
occurs and
• Oligopod stage:- in which last rudiments of abdomen forms
appendages .
• Concurrently with the formation of abdominal appendages a number
of ectodermal invaginations develop from which endoskeletal
components, various glands, the tracheal system ,and certain parts
of the reproductive tract differenciate.

28. ORGANOGENESIS
• Organogenesis is the phase of embryonic development that starts
at the end of gastrulation and continues until the birth.
• During organogenesis, the three germ layers formed from
gastrulation : the ectoderm, endoderm and mesoderm form the
internal organs of the organism.
• Cells of each of the 3 germ layers undergo differentiation ,a process
where less specialized cells become more specialized through the
expression of the specific set of genes.

29. ECTODERM:- outer most germlayer of the developing embryo forms
the brain, and nervous system.
MESODERM:-middle germ layer of the embryo will form blood,
heart,kidney, muscles,and the connective.
ENDODERM:-innermost germ layer of the embryo which gives rise to
gastrointestinal and respiratory organs ,by forming
epithelial linings, and organs such as liver, lungs, and
pancreas.

30. SOURCE – Insect structure and function (by R. F. Chapman)

31. TRACHEAL SYSTEM
• The tracheal system develop from paired lateral in growth ,near the
bases of the appendages, on the meso and meta thorax and on the
first eight abdominal segments.
• The mouths of these invaginations develop and become spiracles,
and their inner ends anterior and posterior longitudinal extensions
meet and fuse to form the main tracheal system.

33. Nervous system
• Shortly after gastrulation the central nervous system develops as a
pair of longitudinal neural ridges of the ectoderm, separated by a
median neural groove.
• The neural ridges becomes segmentally constricted into
neuromeres or primitive nerve ganglia, while their intersegmental
portions give rise to connectives.

34. • It will be noted that the whole of the nervous system and the
sense organs are ectodermal in origin .
• The ganglia of the acron (the unsegmented anterior part of
procephalon) and of the first 3 head segments amalgamate to
form the brain, while the succeding 3 cephalic neuromeres fuse
to become the sub-oesophagal ganglion.
• The neuromeres that follow develop into thoracic and abdominal
ganglion.

36. Alimentary canal
• An in growth of the ectoderm, just behind the antennae, forms the
stomodeum and a corresponding posterior in growth or proctodeum.
• The mesenteron rudiments usually arise as group of cells closely
associated with the stomodeal and proctodeal in growths; these cells
multiply ,grow towards each other finally enclose the yolk in the form of
complete tube- the mesenteron .
• By the disappearance of the walls separating the mesenteron from the
stomodaeum and proctodeum respectively ,a through passage is
established in the alimentary canal.
• The malphigian tubules arise as outgrowths of proctodeum, close to its
union with the mesenteron.

38. CIRCULATORY SYSTEM, MUSCLE AND FAT BODY
• The heart, aorta, musculature ,fat body, lining of the hemocoel, and
some components of the reproductive system are derived from the
somites and median mesoderm formed after gastrulation.
• As noted earlier, the median mesoderm gives rise to hemocytes.
• In most embryos ,each somite becomes hallow and forms 3
interconnected chambers, The anterior, posterior and ventro lateral
pouches.

39. • The splanchnic walls (those facing the yolk) of the two remaining
pouches spread round the gut ,forming the the gut musculature,
some fat body ,and part of the reproductive system.
• The somatic walls (those facing the ectoderm) of the anterior and
posterior pouches give rise to extrinsic limb muscles ,dorsal and
ventral longitudinal
• Other somatic mesoderm cells adjacent to the cardioblasts
differentiate as alary muscles, pericardium septum, and pericardial
cells.
• The aorta develops from the median wall of the antennal somites
which become opposed and grow posteriorly to meet the heart.

42. Reproductive system
• Reproductive system includes both mesodermal and ectodermal
components.
• In females, the vagina and spermatheca develop after hatching as
midventral ectodermal invaginations of the 7th ,8th abdominal
segments.
• Lateral oviducts are paired long tubular canals formed from
mesoderm.
• In males, the ejaculatory duct and ectadenes (ectodermal
accessory glands) are formed from a similar midventral
invaginations of the ectoderm of the 9th or 10th abdominal segment.

44. Because of a molecule or a signalling factor
called “morphogen”
What causes the cells to differentiaate?

45. POST EMBRYONIC DEVELOPMENT
All that takes place after hatching or birth is post embryonic
development.
METAMORPHOSIS :
• It is defined as the series of changes through which an insect passes
in its growth from the egg through the larva and pupa to the adult, or
from the egg through the nymph to the adult.
• These changes are influenced by two hormones namely juvenile
hormone and moulting hormone

46. TYPES OF METAMORPHOSIS
1. Ametabola development
2. Metabola development
Ø Hemimetabola
Ø paurometabola
Ø Holometabola
Ø Hypermetabola
Anamorphic development (anamorphosis)
It is a progressive addition of abdominal segments during the development.
Anamorphosis occurs only in order protura and no any other order of insect;
however, it is known to occur in some other arthropods.

47. AMETABOLUS DEVELOPMENT (EPIMORPHOSIS)
Ø No metamorphosis
Ø More primitive type
Ø Very little or no change during development
Ø Young ones resemble adults
Ø Moulting occurs even during adulthood
Ø Fully developed genetelia found in adults
Ø Eg. Collembolla(springtails),
thysanura(silverfish), diplura(japygids)
Egg - Young one - Adult

48. HEMIMETABOLA
Ø Incomplete metamorphosis
Ø With subsequent moult the wing pads
develop fully and reach adulthood
Ø No pupal stage
Ø Young ones do not resemble adults in all
characters
Ø Habit is different
Ø Eg . Dragonflies, Damselflies,Mayflies
Ø Egg - Naiad - Adult

49. PAURAMETABOLA
Ø Gradual metamorphosis
Ø Young ones resemble adults except
for the presence of fully developed
wings and genetalia.
Ø No pupal staage
Ø Habitat is similar
Ø Eg . Grasshopper ,Cockroach
Ø Egg - Nymph - Adult

50. HOLOMETABOLA
Ø Complete metamorphosis
Ø Stages are structurally dissimilar
Ø Four stages
Ø Pupal stage is present
Ø Habitat is also different
Ø Eg . Butterflies
Ø Egg – Larva – Pupa – Adult

51. Hypermetamorphosis
Ø Holometabolous insects
Ø More than one larval stage
Ø Each larval instar assumes
different forms
Ø Eg . Blister beetle
Ø Egg – Triangulin – Grub – Pupa –
Adult

52. LARVA
• Young ones hatch out of eggs ,active growing stage
TYPES OF LARVA
Ø Mainly three types
1. Oligopod
2. Polypod
3. Apod

53. 1. OLIGOPOD
Ø Head capsule - well developed
Ø Thoracic legs - well developed
Ø Abdominal legs – absent
There are two subtypes
1.Campodeiform 2.Scarabeiform
# Resemble dipluran genus campodidae # Body is ‘C’ shaped
# Thoracic legs are long # Thoracic legs are short
# Generally predators # Sluggish ,burrow into wood or soil
# Eg. Grub of antlion. # Eg. Grub of rhinoceros beetle.

54. 2.POLYPOD OR ERUCIFORM
Ø Body – an elongate trunk
Ø Head capsule – large and sclerotized with powerful mandibles
Ø Eyes – two pairs of stemmata are found
Ø Antenna – short
Ø Three pairs of thoracic legs
Ø Abdominal legs (prolegs) are present on 3,4,5,6,and 10 th segments
Ø Eg. Caterpillar (larva of moths and butterflies)

55. There are three subtypes
1. Hairy caterpillar
• Body hairs – dense or sparsely arranged in tufts
• Eg. Red hairy caterpillar
2. Slug caterpillar
• Small retractile head
• Abdominal legs absent
• Body has poisonous spines called scoli distributed all over the body
• Also called as platyform larva

56. 3. Semilooper
• Prolegs – 3 or 4 pairs
• Prolegs are wanting in either 3rd or 3rd & 4th
abdominal segments
• Eg. Castor semilooper
4. Looper
• Only 2 pairs of prolegs are present
• Prolegs on 6th and 10th segment are present
• Eg. Daincha looper

57. 3.APOD OR VERMIFORM
• Without appendages
• Body is vermiform , appear like worms
• Based on degree of development and sclerotization of head
capsule , three subtypes
1.Eucephalous
• Head capsule – well developed
• Mandibles act – transversely
• Eg. Wriggler (mosquito larva)

58. 2. Hemicephalous
• Head capsule – reduced & can be withdrawn into thorax
• mandibles act – vertically
• Eg. Larvae of horse fly and robber fly
3. Acephalous
• Head capsule – absent
• Mouth parts – a pair of protrusible curved mouth
hooks and associated internal sclerites
• Eg. Maggot (larva of house fly)

59. TYPES OF PUPA
Ø It is the resting and inactive stage in all holometabolous
insects. During this stage. The insect is incapable of feeding
and is quiescent. During this transitional stage , the larval
characters are destroyed and new adult characters are created.
Ø There are differ different types of pupa they are
• Obtect pupa
• Exarate pupa
• Coarctate pupa

60. 1.Obtect
Ø Appendages (antenna,legs,wing pads) – glued to the body
Ø Exposed surfaces of the appendages are more
heavily sclerotized
a. Chrysalis
• Naked obtect
• Angular and attractively coloured
• Attached to substratum by hooks present at the terminal end of
the abdomen called cremaster
• Middle part of the chrysalis is attached to the
substratum by two strong threads called girdle.
• Eg. Pupa of butterfly

61. b.Tumbler
• obtect type, comma shaped with rudimentary
appendages
• Breathing trumpets – present in the cephalic end
• Anal paddles – present at the end of the abdomen
• Jerky movements are produced by the anal paddles
• Very active pupa
• Eg. Pupa of mosquito

62. 2.Exarate
Ø Appendages - not glued to the body , they are free
Ø All Oligopod larvae will turn into exarate pupa
Ø Eg. Pupa of rhinoceros beetle
3.Coarctate
Ø Pupal case – barrel shaped , smooth with no apparent appendages
Ø Last larval skin is changed into a case containing the exarate pupa
Ø Hardened dark brown pupae case is called puparium
Ø Eg. Fly pupa

63. REFERENCES
ØPrinciples of insect morphology by R. E. Snodgrass
ØThe insects: structure and function by R. F. Chapman
ØInsect physiology and biochemistry by James L. Nation