2. Introduction
• The sensory organs are primarily responsible
for the reception of stimuli and pass them on
to the neuro-muscular system, resulting in the
varied behavior patterns of insects.
• Insects can perceive light, sound, scent,
gravity and temperature in minute quantities
often far beyond what can be detected by
other animals.
3. Types of sense organs in insect:
1.Mechanoreceptors
2.Auditory receptors
3.Chemo-receptors
4.Thermo receptors
5.Photo receptors
4. 1.Mechanoreceptors
:
Respond to the sense of
touch due to contact with
external solid objects,
current of air and water or
even because of internal
body pressure.
The principal
mechanoreceptors are:
i.The tactile organs or
trichoid sensilla
ii.The campaniform organs
iii.The chordotonal organs
5. I. Tactile organs or trichoid sensilla
• Formed by two cells
Hair: by Trichogen cell
Socket:by Tormogen
cell
• The dendrite of the neuron
is enclosed at the base of
the hair by a cuticular
tubular sheath,called
scolopale.
• It is in some cases provided
with a distal cap called
scolopale cap.
• It is present on antennae,
tarsi,tibia and cerci of an
insect.
6. ii. The campaniform organs
• Cannot
externally
be seen
but
recognized
dome
from
shaped
cuticle areas
• They occur in
various parts of
body likewing-
base,halters,cerci,
palp and base of
trochanter,femora,
tibia & tarsal
segments.
7. iii. The chordotonal organs
• Consist of single unit or group of
similar units, called Scolopidia.
• They are present in legs at
femoral,distal tibial and tibio-
tarsal regions, in abdomen and
wing base.
• Each scolopidia consists of three
cells
a.Neuron
b.Scolopale cell
c.Cap cell
• Specialized chordotonal organ
a.Johnston’s organ
b.Auditory or Tympanal organ
8. 2. Chemoreceptor (detect smell and
taste)
Chemoreceptor is sensitive to chemicals, stimulation by
chemicals can occur in the following different ways:
1.Olfactory or smell chemoreceptor:
They provide sense of smell. Mechanism of perception
of chemicals in gaseous state at high concentration is
known as olfaction.
1.Gustatory or contact chemoreceptor:
They provide sense of taste. Mechanism of perception of
chemicals in liquid state at high concentration as known
as contact chemoreceptor.
9. Location of chemoreceptor
Organs of taste are common on
I. The mouthparts, especially the palps,
II. The antennae (Hymenoptera),
III. Tarsi (many Lepidoptera, Diptera, and the honeybee),
IV. Ovipositor (parasitic Hymenoptera and some Diptera) and
V. General body surface.
Organs of smell are located on
i.The antennae are the primary site of olfactory organs and
often bear many thousands of these structures.
ii.The mouthparts also carry olfactory structures in many species.
10.
11. 3. Photoreceptors (detect light
energy)
• Ability to perceive light in visible or near visible
range of the electromagnetic spectrum.
• Organism have to be a pigment capable of
absorbing light of a given wave length and a
means of producing a nervous impulse as a
result of this absorption.
Three types of photoreceptivestructures found
in insects:
A. Compound eyes
B. Dorsal ocelli
C. Lateral ocelli (stemmata)
12. A. Compound eyes
• Compound eyes occur in most
adult and hemi-metabolous
larvae on either side of the head
capsule.
• The compound eyes are composed
of a large number of alike
structural units called
ommatidium. The number of
ommatidium varies from insect to
insects.
• Absent is some groups:
a)ancient insect orders (e.g. Protura,
Diplura)
b)wingless parasite adults (lice,
fleas)
c)subterranean termites
d)female scale-insects
e)cave-dwelling forms (sensitivity to
light over the general body surface)
13. B. Dorsal ocelli:
• Visual organs of nymph and it
vary from 0-3 in numbers.
• It contains a single corneal lens
with many visual cells individually
secreting the rhabdomere.
• Dorsal ocelli perceive light to
maintain diurnal rhythm and is
not involved in image perception
C.Lateral ocelli (Stemmata):
• Visual organs of holometabolous
larva.
• Structure is similar to
ommatidium.
• It helps to detect form, colour and
movement, and also to scan the
environment
14. 4. Auditory receptors (detect sound
waves)
i.Delicate tactile hairs:
Present in plumose antenna of male mosquito.
i.Tympanum:
This is a membrane stretched across tympanic cavity
responds to sounds produced at some distance, transmitted
by airborne vibration.
• Tympanal membranes are linked to chordotonal organs
that enhance sound reception.
• Tympanal organs are located
* Between the metathoracic legs of mantids.
* The metathorax of many nectuid moths.
* The prothoracic legs of many orthopterans.
* The abdomen of short horned grasshopper and cicada.
* The wings of certain moths and lacewings.
15. 5. Thermoreceptors (detect heat)
• Present in poikilothermic insects and
sensitive to temperature changes.
• Qualities like warm and cold are most
poikilothermic
important for
organisms like insects that cannot
maintain a constant body temperature.
• During early morning hours
butterflies can be observed, spreading
and directing their wings towards the
sun so that the radiant solar energy
16. 6. Hygro-receptors (detect humidity)
• Insects are
monitor the
water/vapor
able to
amount of
in the
surrounding air.
• Insects actively seek out a
preferred humidity or
sources of liquid water.
• Humidity detectors are
typically located on the
antennae, though they
occur on the spiracles and
their surroundings
