The document discusses various aspects of insect morphology, including types of antennae, their structure and functions. It describes 11 common types of antennae shapes seen in different insects. It also discusses the tentorium, which is the internal skeleton of the insect head, composed of the tentorial bridge and paired anterior, posterior and dorsal tentorial arms. Additionally, it covers insect sense organs like mechanoreceptors, auditory receptors, chemoreceptors, thermoreceptors and photoreceptors. It provides details on the sclerites that make up the insect head, such as the labrum, clypeus, frons, epicranium, occiput and postocciput.

1. ENTO
501

2. Insect Morphology
By Durva Santosh Zulpe

3. 1.Types of antennae
2.Functioning
3.Tentorium
4.Sclerite
5.Insect sense organs

4. Antennae
• Also called as feelers.
• Paired, mobile and segmented.
• Set in a socket of cranium called as antennal
socket.

5. Structure of antennae
• Basal segment – Scape
• Second segment – Pedicel
• Third segment – Flagellum/Clavola

6. Functions
• Detect chemicals.
• Perceives smell, humidity changes, temp.,
wind velocity, wind direction.
• Perceives the forward environment and detect
danger.
• Hearing in mosquitoes and communication in
ants.
• Useful to clasp the mate and grasp prey.

7. Types of Antennae

8. Types of antennae
• 1. Setaceous – size of segments
decreases from base to apex.
Eg. Leafhopper, dragonfly,
damselfly.
• 2. Filiform – segments are
usually cylindrical, thickness of
segments remains same
throughout. Eg. Grasshopper.
• Moniliform – segments are
either globular or spherical with
prominent constriction in
between. Eg. termites

9. • 4. Serrate – segments have
short triangular projections
on one side. Eg. Longicorn
bettle.
• 5. Unipectinate – segments
with long slender processes
on one side. Eg. Sawfly.
• 6. Bipectinate – segments
with long slender lateral
processes on both the sides.
Eg. Silkworm moth

10. • 7. Clavate – Antenna
enlarges gradually
towards the tip. Eg.
Blister beetle.
• 8. Capitate – terminal
segments become
enlarged suddenly. Eg.
Butterfly.
• 9. Lamellate – Antennal
tip is expanded laterally
on one side to form flat
plates. Eg. Lamellicorn
bettle.

11. • 10. Aristate – the terminal
segment is enlarged. It
bears a conspicuous dorsal
bristle called arista. Eg.
House fly
• 11. Stylate – terminal
segment bear a style like
process. Eg. House fly,
robber fly.
• 12. Plumose – segments
with long whorls of hairs.
Eg. Male mosquito.

12. • 13. Pilose – antennae is less
feathery with few hairs at the
junction of flagellomeres. Eg.
Female mosquito.
• 14. Geniculate – Scape is long
remanining segments are small
and are arranged at an angle to
the first resembling an elbow
joint. Eg. Ant, weevil and
honeybee.
• 15. Flabellte – very small, third
and subsequent segments with
side processes giving a fan like
arrangements. Eg.
strepsipterans, cedar beetles.

13. Sense organs
• Sensilla are the organs associated with sensory
perception and develop from epidermal cells. The
different types of sense organs are :
• 1. Mechano receptors
• 2. Auditory receptors
• 3. Chemo receptors
• 4. Thermo receptors
• 5. Photo receptors

14. Mechano receptors
• Hair like sense organ.
• Cells are sensitive to touch and located in antenna
and tropi.
Trichoid
sensilla
• Terminal end is rod like.
• Cells are sensitive to pressure and located in leg
joints and wing bases.
Campaniform
sensilla
• Specialized sensory organs that receive vibrations.
• Consists of one to many scolopidia, each of which
consists of cap cell, scolopale cell and dendrite.
Chordotonal
organ

16. Functions of Mechano receptors
• Proprioception : Positioning of their body parts in
relation to the gravity.
• Sensitive to sound waves, vibration of substratum
and pressure changes.
• Johnston’s organ : All adult insects and many
larvae have Johnston’s organ lying within second
antennal segment. Sense movements of antennal
flagellum. Function in hearing in some insects like
male mosquitoes and midges.
• Subgenual organ : Found in most insects, expcept
Coleoptera and diptera. Detect substrate
vibrations.

17. Auditory receptors
• 1. Delicate tactile hairs : present in plumose
antennae of male mosquito.
• 2. Tympanum : this membrane is stretched across
tympanic cavity responds to sounds produced at
some distance.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, cicada.
The wings of certain moths and lacewings.

19. Chemo receptors
• Detect chemical energy.
• Insect chemoreceptors are sensilla with one pore
or more pores.
• Gustatory receptor : Uniporous chemoreceptors
detect chemical of solid and liquid form by
contact.
• Olfactory receptors : Multiporous
chemoreceptors detect chemicals in vapour form,
at distant by smell.
• Each pore forms a chamber known as pore kettle.

21. Thermo receptors
• Present in poikilothermic insects and sensitive
to temperature changes.
• In bed bug it is useful to locate the host
utilizing the temperature gradient of the host.

23. Photo receptors
• Based on many individual units called ommatidia.
• Made up of two parts optic part and sensory part.
• Optic part : contain lens called corneal lens and crystalline
cone covered by primary pigment cells. Functions to gather
light.
• Sensory part : Six to ten visual cells called retinular cells called
rhabdom. Rhabdom contains light sensitve pigments called
rhodopsin.
Compound
eyes
• Visual organs of holometabolous larva.
• Helps to detect form, colour and movement, and
also to scan the environment.
Lateral ocelli
(Stemmata)
• Visual organs of nymph and it vary from 0-3 in
numbers.
• Dorsal ocelli perceive light to maintain diurnal
rhythm and is not involved in image perception.
Dorsal ocelli

25. Sclerites
• Represents the inter sutural areas.
• Common sutures found in insect head are :
• 1. The labrum
• 2. Clypeus
• 3. Frons
• 4. Epicranium
• 5. Occiput
• 6. Post occiput

26. Insect Head

27. The Labrum
• Also known as upper lip in mandibulate
insects.
• Freely attached to lower margin of the clypeus
by the clypeolabral suture.
• Internally lined with the gustatory receptors
and can be moved upwards and downwards.
• The labrum is innervated by compressor
labral, the anterior labral and posterior labral
muscles.

32. The post occiput
• The occipital foramen is encircled from the
dorsal and lateral regions by a narrow sclerite
called the post occiput.
• It lies between the occiput and the neck.
• Post occiput is seperated from the occiput by
post occipital suture.
•

33. The genae and subgenal areas
• The genae represents lateral area of the head.
• The genae extend from the compound eye to
the mandibular trochantin on both sides.
• Posterior to the occipital suture each lateral
genae is commonly called as post genae.
• The subgenal areas above and below the
mandibles are called as pleurostoma and
hypostoma resp.

34. The occular sclerites
• They form cuticular ring around each
compound eyes.
• The antennal sclerites form and annulus at the
base of each antennae.
• The mandibular trochantin occurs between
the mandibular base and the pleurostroma.

35. Insect Tentorium

36. Tentorium
• The tentorium is the internal skeleton of the head capsule
of insects.
• In insects, the integument is occasionally invaginated into
the body cavity to form and internal, skeleton support.Such
a structure is termed an apodeme.
• The various apodemes together comprise the
endoskeleton. The tentorium is the endoskeleton of the
insect head and is composed of four parts, viz., the
tentorial bridge, a pair of the anterior and posterior
tentorial arms and the dorsal tentorial arms.
• In addition to these, the tentorium often possesses various
processes arising from the anterior tentorial arm, posterior
arm or tentorial bridge in some Orthoptera.