Reproductive system in insect and its types

Prepared by:
Nandini HK
Suresh R. Jambagi
M.Sc. (Agri) Agril. Entomology
University of Agricultural Sciences
Dharwad, Karnataka-580005
Email: jambagisuru@gmail.com
GENERAL ENTOMOLOGY
Presentation: 8
Topics covered : i) Male reproductive system in insects
ii) Female reproductive system in insects
iii) Types of reproduction in insects

REPRODUCTION IN INSECTS
 Usually Insects are bisexual. But sometimes reproduction also
occurs by Parthenogenesis and hermaphroditism (Cotton
cushion scale).
 The reproductive system is divided in to two parts namely internal
genitalia and external genitalia. The internal genitalia serve to the
development of germ cells.
 The external genitalia accomplish the union of two sexes and
enable the female to deposit eggs.
Suresh Jambagi M.Sc (Agri) Entomology UAS
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A. FEMALE REPRODUCTIVE SYSTEM
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It consists of:
 a pair of ovaries which possess number of ovarioles,
 a pair of oviducts,
 Common oviduct / Median oviduct,
 Spermatheca,
 a pair of accessory glands and
 Bursa copulatrix or copulatory pouch or genital
chamber or vagina
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1. Ovaries:
 These are the prominent visceral organs present on the either
side of alimentary canal.
 Anteriorly the ovaries get connected with the body wall by
means of thread like suspensory ligaments.
 The ovaries are covered with fat body and are richly covered
with trachea.
 Each ovary consists of a no of ovarioles or egg tubes.
 Ovarioles: Each ovariole is enveloped by a double layered
cellular wall.
 The outer wall is called ovarial sheath which has an
abundant supply of tracheae.
 The inner layer called tunica propria is elastic in nature.
 Each ovariole at its terminal has a filament which unites with
other filaments.
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 Suspensary ligament: The ligament is attached to the
body wall or dorsal diaphragm and thus helps the ovaries
to remain suspended at a proper place .
 The eggs are discharged in to the lateral oviducts.
Lateral oviducts: Proximal end of the ovarioles of each
ovary join to form a lateral oviduct on each side.
 The wall of oviduct is glandular and muscular.
Median Oviduct: Two lateral oviducts combine to form
a median oviduct.
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 Vagina: In most of the insects median oviduct does not
open directly to outside.
 It opens in to a tubular genital chamber or vagina formed
by invagination of bodywall from VIII segment.
 The vagina opens outside and the opening is called vulva.
Vulva serves both purposes of receiving the sperms and
discharging the eggs.
 Bursa Copulatrix: In some insects the genital chamber
or vagina develops a separate pouch called Bursa
Copulatrix .
 Insects have two reproductive openings. One is vulva for
receiving the sperms open on VIII sternum and another
one is ovipore or gonopore on IX segment for discharging
eggs.
Ex: Lepidoptera and water beetles
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 Spermatheca: It is a sac like structure consisting of a
spermathecal gland and opens in to vagina through
spermathecal duct.
 This is mainly used for storing the sperms.
 It also produces some fluids responsible for longevity of
cells for several hours.
Accessory glands: These are a pair of collateral glands
which open in to the distal portion of vagina and secrete
the substance responsible for the formation of ootheca of
cockroach, preying mantid.
 Poisonous secretions in case of Hymenoptera.
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 Each ovary in insects consists of a group of tapering units
called ovarioles.
 The number of ovarioles in an ovary varies greatly in
different insects, usually 4 to 8.
 In Isoptera more than 2000.
 Typical ovariole or egg tube consists of 3 parts namely
1. Terminal filament
2. Egg tube
3. Supporting stalk or pedicel
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1. Terminal filament: of all the ovarioles in a ovary
unite distally with one another in a suspensory
ligament.
 The ligaments from the two ovaries are combined in
a single median ligament which is attached to the
tergal plated of thorax.
 The Egg tube is divided in to two parts
a. Egg chamber or Germarium
b. Zone of growth or vitellarium
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a. Germarium: Also called as egg
chamber which contain the primordial
germ cells or undifferentiated cells.
These cells give rise to three types of
cells.
a. Germ cells developing in to oogonia
and dinally oocytes
b. Nutritive cells or nurse cells
trophocytes.
c. Follicle cells
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b. Vitellarium or Zone of growth: It occupies the major
part of the ovariole and contains large number of oocytes
and eggs in different stages of development.
• The egg cells grow and attain their mature stage.
• In the anterior region of vitellarium the nurse cells and
oocytes remain mixed up and assume the central position
while follicle cells take peripheral position.
• In posterior end oocytes are enclosed by follicle cells to
form follicular layer.
• The nurse cells absorb nutrients from haemolymph
through follicular cells and transmit them to oocytes.
• In some case follicle cells provide nutrients to the
oocytes where nurse cells are absent.
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 Types of ovarioles:
Based on the presence or absence of nutritive cells
and their location ovarioles are categorized in to two-
1. Panoistic ovarioles: In these, the nutritive cells are
absent and the development of oocytes takes place with
the help of follicular epithelial cells.
Ex: Odonata, Dictyoptera, Orthoptera and Ephemeroptera
2. Meriostic ovarioles: They contain trophocytes / nutritive
cells which vary in their position.
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 Based on the position of trophocytes Meriostic ovarioles
are classified into
(i) Polytrophic ovarioles: where developing oocyte and
trophocytes arranged alternatively within the vitellarium.
Ex: Mecoptera, Dermaptera, Psocoptera
(ii) Acrotrophic ovarioles: Also called teletrophic ovarioles
where the trophocytes are present in the germarium (apex)
and are connected with the growing or developing oocytes
by cytoplasmic strands.
Ex: Hemiptera and Coleoptera.
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 Internal male reproductive
organs consists of
 a pair of testis,
 a pair of vasa deferens,
 seminal vesicle
 ejaculatory duct
 accessory glands-
a) mesodenia b) ectodenia
 Genitalia
B. MALE REPRODUCTIVE SYSTEM
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1.Testis: The size of testis is practically same as that of
ovaries in Apterygota and very much smaller in Pterygota .
 They lie in visceral cavity above the alimentary canal and
are connected to the body wall through translucent ducts
and are well supplied with trachea and fat body tissues.
 Each testis consists of number of oval shaped structures
known as follicles or sperm tubes.
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 Each follicle has a layer of epithelial cells. The entire
follicle is covered by a peritoneal membrane where as the
testis is completely enveloped within a coat known as
scrotum.
Structure of follicle: Each individual follicle is divided
into a series of zones (or) areas characterized by the
presence of the sex cells i.e. sperms in different stages of
development.
 These zones are zone of germarium, zone of growth, zone
of division and reduction and zone of transformation.
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i. Germarium: It is the region containing primordial
germ cells or spermatogonia which undergo
multiplication (Zone of spermatogonia).
ii. Zone of growth: It is the area where spermatogonia
increase in size, undergo repeated mitosis and
develop in to spermatocytes (Zone of spermatocytes)
iii. Zone of division and reduction: It is the area
where spermatocytes undergo meiosis and give rise
to spermatids (Zone of spermatids)
iv. Zone of transformation: It is the area where
spermatids get transformed in to spermatozoa (Zone
of spermatozoa).
• Spermatozoa are a group of cells which are enclosed
in testicular cyst cells from which they are released
in to vasa efferens, the tubular connections of the
follicles which combine together to form the vasa
deferens.
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2. Vasa deferens: These are the long tubes formed by the
union of vasa efferens which receives the sperms from
testis and allow their transport to the ejaculatory duct.
3.Seminal vesicles: Each vasa deferens becomes enlarged
posteriorly to form a sac like structure called seminal
vesicle for storage of spermatozoa for some time.
4. Ejaculatory duct: Both the vasa deferens of the two testes
unite posteriorly to form a common median ejaculatory
duct.
 The terminal section of ejaculatory duct is enclosed in a
finger like evagination of body wall, male copulatory organ
or aedeagus or penis.
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5. Accessory glands: These are 1-3 pairs of glands which
open in to the ejaculatory duct. In most cases their
secretion mix with spermatozoa. These glands are called
mushroom glands in cockroaches and mantids because of
their appearance as mushrooms. This secretion facilitates
sperm transmission from male to female.
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 Types of Reproduction:
Insects are bisexual, they can undergo sexual reproduction
for producing either the eggs (or) the young ones. However they
also reproduce by other means.
 Different types of reproduction in insects are:
1. Oviparity: Insects reproduce by laying eggs by the female on
any substrate either singly (or) in mass (or) in groups which
later hatch and produce the young ones.
Ex: moths and butterflies.
2. Viviparity: It is the phenomenon of reproduction where the
female gives birth to the young ones instead of laying eggs.
 Embryonic development is completed within the female and the
embryo gets nourishment from the mother and produces the
larva/young ones within the haemocoel.
 These young ones after some time emerges out from the
mother, based on the source of nourishment.
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Viviparity is classified in to 4 types-
i. Ovo-viviparity: Insects retain the eggs within the genital track
until the eggs are ready to hatch (or) giving birth to young ones.
 However immediately after hatching , the young ones will be
released outside.
 Hence, no special structures are developed for nourishment.
Ex: Thysanoptera
ii. Adenoparous viviparity: It is a type of viviparity where the
eggs have sufficient yolk, complete their embryonic
development and retain in the uterus.
 Eggs hatch and the young ones get nourishment from special
nourishment glands called milk glands which contains milk that
have lipids and proteins.
 When young ones are fully developed, it emerges from the
mother and forms in to a pupa within short time and no
feeding phase is seen.
Ex: Glossina pupipara of Diptera.
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iii. Pseudo placental viviparity: It is a phenomenon where insect
have eggs with little (or) no yolk.
 Hatching takes place within the mother and the nourishment for
the young one is received through embryonic maternal structure
called pseudo placenta.
Ex: Psocoptera, Dermaptera, aphids etc
iv. Haemocoelous viviparity: It is a type of reproduction where
the eggs are retained within the haemocoel and the embryonic
development as well as the nourishment of young one takes
place through the transfer of nutrients from the haemolymph
of mother.
 After development, young one comes out either through
genital canal or by the rupture in the walls of the parent.
 Eggs have no chorion but become surrounded from an early
stage by a trophic membrane through which nutrient material
are supplied from the maternal tissues.
Ex: strepsipterans & some larvae of cecidomyids (Diptera)
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3. Parthenogenesis: It is the ability of the females to
reproduce without fertilization / copulation with males. This
usually occurs due to the genetic characters, due to heredity,
failure in finding a mate, hormonal changes within the body
and weather factors.
 This parthenogenesis is classified as
I. Based on the occurrence-
i. Sporadic parthenogenesis: occurs occasionally. Ex:
silkworm.
ii. Constant parthenogenesis: occurs regularly. Ex: thrips
iii. Cyclic parthenogenesis: it is nothing but the alternation
of generations where parthenogenesis occurs in alternation
with the sexual reproduction. Ex: aphids.
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II. Based on the sexes of the off springs produced-
i. Arrhenotoky: only males are produced
e.g.: Hymenoptera
ii.Thelytoky: only females are produced e.g.: acridids
iii. Amphytoky: Both females and males are produced e.g.:
hymenopterans
4. Paedogenesis (or) Neoteny: It is a phenomenon where the
immature insects or stages give birth to young ones.
 This usually occurs due to the hormonal imbalance.
 Most of the insects which reproduce by paedogenesis also
reproduce by parthenogenesis.
Ex: cecidomyids.
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5. Polyembryony: It is a type of reproduction where insects reproduce
by giving birth to two or more young ones instead of a single one, as
two or more embryos are produced from a single egg.
Ex: Endo parasitic Hymenoptera like platygaster
6. Hermaphroditism: It is a type of reproduction where both male and
female gonads are present in the same individual.
 It may be a functional hermaphroditism as in case of Icerya purchsi
(or) non functional as in case of stonefly, Perla marginata.
7. Castration: It is a type of reproduction where the separation of the
individuals occurs mainly due to the development of the reproductive
organs.
 The insects with well developed ovaries develop in to females
(queens), the insects with well developed testis develop in to males
(drones) and insects with underdeveloped ovaries develop in to
workers.
Ex: social insects such as honey bees.
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8. Alternation of generation: Insects reproduce by
parthenogenesis and bisexual reproduction by alteration of
generations. Ex: aphids which reproduce by
parthenogenesis in summer and undergo sexual
reproduction in winter.
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