Insects have a variety of sense organs to detect mechanical, auditory, chemical, thermal, and visual stimuli. Mechanoreceptors include trichoid sensilla for touch and campaniform sensilla and chordotonal organs for vibration/pressure. Auditory receptors include tympana and tactile hairs. Chemoreceptors detect smells and tastes. Thermoreceptors sense heat. Compound eyes contain many ommatidia that form distinct images for diurnal insects or blurred images for nocturnal insects. Simple eyes include lateral ocelli in larvae and dorsal ocelli in nymphs.

1. SENSE ORGANS
IN INSECTS
Prepared by
Dr. S. Sumaiya

2. Sense organs
1. Mechano
receptors
2. Auditory
receptors
3. Chemoreceptor
s
4. Thermo
receptors
5. Photo
receptors
Sensilla – organs of
sensory perception

3. Mechano receptors
detect mechanical forces
• Trichoid sensilla
• Campaniform sensilla
• Chordotonal organs
Trichoid sensilla
• Hair like little organ
• Sense cell associated with spur and seta
• Sensitive to touch
• Located in antenna and mouthparts

4. Mechano receptors
Campaniform sensilla
• Dome sensilla
• Terminal end – rod like and
inserted into dome shaped
cuticula
• Sensitive to pressure
• Location : leg joints and wing
bases

5. Mechano receptors
Chordotonal organs
• Specialized sensory
organs that receive
vibrations are subcuticular
mechanoreceptors
• Consists of one or more
scolopidia
• Each of which consists of
cap cell, scolopale cell and
dendrite
• Attached to both ends of
body wall

6. Chordotonal organs - Functions
• Proprioception
• positioning of body parts in relation to the gravity
• Sensitive to sound waves, vibration and pressure
• Johnstons organ
• Second antennal segment (pedicel)
• Sense movements of antenna flagellum
• Hearing function – male mosquitoes
• Subgenual organ
• Located in proximal tibia
• Detect substrate vibration
• Not in coleopteran and diptera

7. Auditory receptors
• Tactile hairs: plumose antenna of male mosquito
• Tympanum: this is a membrane stretched across
tympanic cavity responds to sounds produced at some
distance, transmitted by air borne vibration.
Location Example
Between metathoracic
leg
Meta thorax
Mantids
Noctuid moths
Prothoracic legs Orthopterans
Abdomen Short horned
grasshopper
wings Moths and lace wings

8. Chemoreceptors
detect smell and taste
• Gustatory receptor – uniporous – detect chemicals
of solid and liquid form by contact
• Olfactory receptor – multiparous – located in
antenna – detect chemicals in vapour form at
distant by smell
• Each pore forms a chamber – pore kettle
Thermoreceptors
detect heat
• Poikilothermic insects
• Sensitive to temperature
changes
• Bed bug – locate host

9. Photoreceptors
• compound eyes are composed of
many similar, closely-packed
facets (called ommatidia) which
are the structural and functional
units of vision.
• Externally, each ommatidium is
marked by a convex thickening of
transparent cuticle, the corneal
lens.
• Beneath the lens, there is often a
crystalline cone secreted by a pair
of semper cells.
• The light-sensitive part of an
ommatidium is called the
rhabdom.
• The rhabdom contains an array of

10. Types of ommatidia
i. Apposition type (light tight):
• Due to the presence of primary pigment cells light
cannot enter the adjacent cells.
• The mosaic image formed is very distinct.
• The image formed by the compound eye is of a series
of opposed points of light of different intensities.
• This functions well in diurnal insects.
ii. Super position type:
• Primary pigment cells are absent allowing light to pass
between adjacent ommatidia.
• Image formed in this way are indistinct, bright and
blurred.
• This type is seen in nocturnal and crepuscular insects.

11. Simple eyes
A. 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.
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.