Respiratory system in insect

Prepared by:
Vidya K. C
Suresh R. Jambagi
M.Sc. (Agri) Agril. Entomology
University of Agricultural Sciences
Dharwad, Karnataka-580005
Email: jambagisuru@gmail.com
GENERAL ENTOMOLOGY
Presentation: 5
Topics : Respiratory system in insects

Tracheal system: In insects, exchange of gases takes place through tubular structures,
called trachea.
 They are distributed throughout the body collectively forming tracheal system. These
trachea open outside on the body wall through small openings called spiracles.
 Spiracles occur on the pleural surfaces of the body, one on either side of each
segment.
 The tracheae are divided in to very fine branches known as tracheoles. They supply
oxygen to the body tissues.
 The tracheal system with functional spiracles is called the open tracheal system and
with non-functional spiracles is called closed tracheal system.
RESPIRATORY SYSTEM
Suresh Jambagi M.Sc (Agri) UAS Dharwad
2

 Tracheae are fine elastic tubular structures which are
ectodermal in origin.
 They consist of cuticle, epidermis, basement
membrane as in case of general body wall but arranged
in reverse manner, i.e. basement membrane forms the
outermost coat of trachea.
 The inner cuticular lining forms the intima inside.
 Tracheae are circular or elliptical in their cross
section.
 The cuticular lining (intima) appear as a spiral
thickening throughout the length of the tube of trachea.
 These spiral thickenings are known as ‘taenidia’
which give support to the trachea without being
collapsed when there is no air.
Suresh Jambagi M.Sc (Agri) UAS Dharwad 3

 It consists of chitin, resilin in protein-chitin matrix.
 The trachea ramify into very fine branches known as ‘tracheoles’ which are about 0.1 –
1 μm in diameter (Fig. 32).
 These tracheoles are formed in to cells called ‘tracheoblast’ or tracheolar end cell,
which are derived from epidermal cells, lining the trachea.
 Tracheoles form a network over the visceral organs including the alimentary canal as
well as the gonads (ovaries, testis) and penetrate in to the tissues of the organs and
become intracellular and supply oxygen directly to the tissues.

Differences between trachea and tracheoles
Trachea
• These are large tubes running from
spiracles
• Taenidia present
• Intima layer is shed during moulting
• Never become intracellular
• The intima layer consist of protein –
• chitin matrix with resilin
Tracheoles
• Fine tubes arising distally from
trachea
• Absent
• Intima layer is retained, unchanged
during moulting
• Intracellular
• Chitin – protein matrix present,
resilin absent

Tracheal trunks: The trachea coming from spiracles through out the body join with
those of neighbouring spiracles forming ‘longitudinal trunks’. Likewise, these
tracheae by combining with those coming from dorsal, lateral and ventral sides of the
body fuse to form transverse commissures and longitudinal connectives. All these
in total form into dorsal trunk, lateral trunks which are two in number and one
ventral trunk.
The dorsal trunk supply oxygen to proximal part of the body as well as to heart
where as the ventral supplies to the central nervous system. The two lateral
longitudinal trunks spread tracheoles to alimentary canal, legs, gonads and wings.
As the head do not contain spiracles, air is supplied through the first pair spiracles by
means of two main branches of the dorsal longitudinal trunk, where one branch
supply O2 to eyes, antenna, brain; other branch to mouthparts and muscles of the
head.
6

Spiracles: They are the openings of the internal tubular trachea. Except in Diplura, in all
the orders, spiracles are absent in prothorax and distributed in meso, metathorax and
abdomen.
 A total of 10 pairs are present in general, 2 pairs in thorax and 8 pairs in abdomen.
Spiracles are situated on pleural surface. They consist of a small ring like sclerite at
opening called ‘peritreme’ leading to a cavity known as ‘atrium’.
 The closing and opening of spiracles is accompanied by atrial valve lined with
fibrous processes and form so called felt chamber which reduces water loss in the
absence of closing mechanism.
 In some dipterans, coleopterans, lepidopterans, spiracles consists of sieve plate
containing large number of small apertures through which gas exchange takes place.
This modification is to prevent entry of water especially in aquatic forms.
 In most of the terrestrial insects, water loss through spiracles is controlled by the
closing mechanism which consists of one or two valves or a constriction from the
trachea or by muscular activity. The hydrophobic nature of spiracles is also due to the
presence of modified epidermal glands known as peristigmatic glands which secrete
a hydrophobe material preventing the wetting of these organs.
7

Classification of tracheal system based on number and
arrangement of functional spiracles
In most of the insects, 10 pairs of spiracles are present. Some of the modifications
are as follows
I. Holopneustic: These are primitive type with 2 pairs of spiracles on thorax and 8 pairs on
abdomen. All the spiracles are functional. 1 + 1 + 8.
Ex: Dragonflies, Grasshoppers and Cockroach
II. Hemipneustic: One or more pairs of spiracles become non-functional. They are
a) Peripneustic: Metathoracic spiracle is closed. 1 + 0 + 8.
Ex: larvae of Lepidoptera, Hymenoptera, Coleoptera.
b) Amphipneustic: Only mesothoracic and last pair of abdominal spiracles are
open. 1+0+ 1.
Ex: larva of cyclorrhaphan Diptera.
c) Propneustic: Only one pair i.e. mesothoracic spiracles are open, 1 + 0 + 0
Ex: mosquito pupa
d) Metapneustic: Only last pair of abdominal spiracles are open. 0 + 0 + 1.
Ex: mosquito larvae
e) Apneustic: No functional spiracles.
Ex: mayfly larva, nymph of Odonata
8

III. Hypopneustic: 1 or 2 pairs of spiracles may completely disappear or absent
Ex: Siphunculata, Mallophaga
IV. Hyperpneustic: More than 10 pairs of spiracles are present
Ex: Japyx sps. (dipluran)
Other types of respiration:
1. Cutaneous respiration: When the spiracles are absent, respiration occurs through body
wall which forms main source for gaseous exchange.
Ex: Protura, Collembola and endoparasitic insects.
2. Tracheal gills: Also called as abdominal gills which occur as the outgrowths of the
trachea in the form of gills distributed on the lateral sides of the body. They are useful for
absorption of dissolved oxygen. They may vary in shape as lamellate or filamentous.
Ex: larva of Trichoptera, nymphs of Ephemeroptera
3. Spiracular gills: Peritreme or atrium of spiracles is drawn out in to a long filament like
structure known as spiracular gills. These gills are adapted for both aquatic and aerial
respiration, enabling the insect to live in air and moist places or completely in water or at
the edges of water structures.
Ex: In some aquatic pupae

4. Blood gills: These are tubular or digitiform or eversible structures present at the anal end of
body ranging from 4-6 in larva of Trichoptera. In chironomid larva of Diptera, 2 pairs of
blood gills are present on penultimate segment and a group of 4 shorter anal gills are present.
These are called blood gills as they contain blood but some times have trachea. Function of
these structures is the absorption of water and inorganic ions rather than respiration.
5. Rectal gills: In dragonfly nymphs (naiads), the rectum modifies in to a barrel like
chamber where the rectal wall forms in to basal thick pads and distal gill filaments which are
richly supplied with tracheoles. They help in respiration.
6. Air sacs: In many winged insects, the trachea get dilated at some points to form thin walled
air sacs which do not contain the taenidia. These can be seen as glistening sac like structures
mainly function as storage structures of air which change their volume with respiratory
movement.
7. Plastron respiration: The plastron is a special type of air store in the form of a thin film
held by a system of hydrofuge hairs, scales or other cuticular processes whose volume
remains constant. If there is adequate oxygen dissolved in water, the plastron can act as a
permanent physical gill. The trachea opens in to plastron.
Ex: aquatic beetles.

Respiratory system in insect

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Respiratory system in insect

Similar to Respiratory system in insect (20)

More from Mr. Suresh R. Jambagi

More from Mr. Suresh R. Jambagi (16)

Recently uploaded

Recently uploaded (20)

Respiratory system in insect