Pra embryonic and post-embryonic development in insect
• Pre-embryonic Development
• Embryonic Development
• Post-embryonic Development
• The sperm swim toward the micropyle -- the first one to
reach its destination enters and injects its nucleus into the
• The sperm nucleus quickly fuses with the egg nucleus to
form a diploid zygote -- a one-celled embryo.
• This event is known as fertilization.
• After the egg is fertilized, it undergoes a period of rapid
growth and development known as embryogenesis.
• The micropyle, a special opening near the anterior end of
the chorion, serves as a gateway for entry of sperm during
• A female receives sperm from her male partner during the
act of mating---insemination
• She can store that sperm for long periods of time in a
special part of her reproductive system, the
• As a developing egg moves past the opening to the
spermatheca, a few sperm are released onto its surface.
In most insects, life begins as an independent egg.
This type of reproduction is known as oviparity.
Manufactured within the female's genital system
Released from her body through an ovipositor
Production of eggs by the female is called oogenesis
The egg-laying process is known as oviposition.
• Each insect species produces eggs that are genetically
unique and often physically distinctive as well --
spherical, ovate, conical, sausage-shaped, barrel-shaped,
• Each egg is composed of only a single living cell -- the
• The egg is covered by a protective
"shell" of protein secreted before
oviposition by accessory glands in
the female's reproductive system.
• This egg shell, called the chorion ,
is sculptured with microscopic
grooves or ridges that may be
visible only under an electron
• The chorion is perforated by
microscopic pores (called aeropyles
) that allow respiratory exchange of
oxygen and carbon dioxide with
relatively little loss of water.
expulsion of egg from
eggs incubated in
upon being laid
Giving birth to
forms of this are
seen in insects.
Placental (aphids), haemocoelus
(hemocoel, gall midges), adentrophic
(nurse gland, fully grown larva tsetse fly.
The main type of Reproduction
The Other Type of
Reproduction In Insect
– Reproduction by larval insects
– Development without fertilization
– Unfertilized eggs produce:
• Males (arrhenotoky) in Hymenoptera
• Females (thelytoky)
• Both (amphitoky) in aphids, some wasps
• Found in some endoparasitic groups only
• Single egg results in 2 to ‘several thousand’
• Some larvae may be ‘defender morphs’
– Hatch more quickly
– Eliminate rival parasites
– Fail to pupate & they die
• Remaining larvae become ‘reproductive
morphs’ that complete development and
reproduce to carry on the species
A developmental process that usually begins once the
egg has been fertilized.
It involves multiplication of cells (by mitosis) and their
subsequent growth, movement, and differentiation into
all the tissues and organs of a living insect.
Developmental Fate of Insect Germ Layers
• Ectoderm: Epidermis, exocrine glands, brain and
nervous system, sense organs, foregut and hindgut,
respiratory system, external genitalia.
• Mesoderm: Heart, blood, circulatory system,
muscles, endocrine glands, fat body, gonads
• Endoderm: Midgut.
Embryonic development of
M. sexta egg
.Manduca sexta eggs.
M. sexta embryo 19
hours after fertilization
M. sexta embryo 37
hours after fertilization
M. sexta embryo 57
hours after fertilization
M. sexta embryo 115
hours after fertilization.
Newly emerged larva
showing the head
Summary of Insect Development
Yolk distribution- centralized
Cleavage type - meroblastic, only portion of yolk undergoes
Gastrulation- ingression and invagination
Blastospore type- protostome (mouth and anus from
Larval development- multiple molts, maggot, nymph, caterpillar,
pupa, adult (imago)
Developmental determination- mosaic pattern
• Once the hatching emerges, it is called a
first instar nymph (or larva).
• As it grows, it will continue to develop and
• These post-embryonic changes are known
• Once an insect hatches from the egg it is usually able to
survive on its own, but it is small, wingless, and sexually
• Its primary role in life is to eat and grow.
• If it survives, it will periodically replace its exoskeleton
(a process known as molting).
• In many species, there are other physical changes
that also occur as the insect gets older (growth of
wings and development of external genitalia, for
• Collectively, all changes that involve growth,
molting, and maturation are known as
• The molting process is triggered by hormones released
when an insect's growth reaches the physical limits of its
• Each molt represents the end of one growth stage (instar)
and the beginning of another
• In some insect species the number of instars is constant
(typically from 3 to 15), but in others it may vary in
response to temperature, food availability, or other
• Molting stops when the insect becomes an adult --
energy for growth is then channeled into production of
eggs and sperm.
• An insect cannot survive without the support and
protection of its exoskeleton, so a new, larger
replacement must be constructed inside the old one --
much like putting an overcoat under a sweater!
• An insect that is actively constructing new exoskeleton is
said to be in a pharate condition.
• During the days or weeks of this process there may be very
little evidence of change.
• Ecdysis, however, occurs quickly (in minutes to hours).
• A newly molted insect is soft and largely unpigmented
(white or ivory).
• It is said to be in a teneral condition until the process of
tanning is completed (usually a day or two).
Summary of 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
• fixed in size
• new exoskeleton
Incorporates the changes that are part of
Initially soft and is larger than the old exoskeleton.
• Stages between each molt are called instars.
first stage which emerged from the egg is the first
instar or nymph.
-- to grow must shed its skin or molt
-- may be four or five instars before the adult stage is reached
An adult cicada (Homoptera)
just after molting