Insect Morphology and Systematics
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ORGANS OF RESPIRATION
SPIRACLES
Spiracles have a chamber or
atrium
with a opening and closing mechanism called
valve
.
This regulates air passage and minimise water loss. Each spiracle is set in a sclerotized cuticular
plate called a
peritreme
. Tracheae are invaginations of the epidermis and thus their lining is
continuous with the body cuticle. The ringed appearance of the tracheae is due to the spiral ridges
called
taenidia
. This allows the tracheae to be flexible but resist compression. The cuticular
linings of the tracheae are shed when the insect moults, but not the linings of tracheoles.
Tracheoles
are less than 1
m in diameter; they end blindly and closely contact the
respiring tissues. Taenidia and waxlayer is absent. Cuticulin layer is permeable to gases. It is
intracellular in nature, but enclosed only in the cytoplasm of tracheal and cell called
tracheoblast
.
Gaseous exchange occurs across tracheoles.There are four tracheal trunks viz., lateral, dorsal,
ventral and visceral, helping in the passage of air.In the trachea, thin walled-collapsable sac like
dilations are present, called as
airsacs
where taenidia is absent. Airsacs acts as oxygen
reservoir. Provide buoyancy to flying and aquatic insects. Provide space for growing organs. Acts
as sound resonator and heat insulators.
Insect Morphology and Systematics
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83
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