Prepared by : Reem Alajmi
• Insect in relation to other Arthropod (introduction)
• Insect general morphology
• Head and its appendages
• Thorax and its appendages
• Abdomen and its appendages
• The structure and function of integument
• Internal organs:
• The digestive system
• The execratory system
• The circulatory system
• The nervous system
• The respiratory system
• The endocrine system
• Insect development (Metamorphosis)
• Insects classifications
• Lab Exam
• Lab Notebook
• Insect Collection
All arthropods possess
• Exoskeleton - a hard protective covering around the
outside of the body (divided by sutures into plates
• Segmented body - that allows movement
• Jointed limbs and jointed mouthparts - that allow
• Bilateral symmetry - whereby a central line can
divide the body into two identical halves, left and
• Ventral nerve chord - as opposed to a vertebrate
nerve chord which is dorsal
• Dorsal blood vessel
Major groups of Arthropods
Class Arachnida (Scorpions & Spiders)
Class Chilopoda (Centipedes)
Class Diplopoda (Millipedes)
Class Crustacea (Shrimps, Crabs, Lobsters)
Class Insecta (Insects)
All insects possess
• 3 body parts (head, thorax and abdomen)
• 6 legs
• 1 pair antennae
• Most adults have wings
• Strongly sclerotized rigid capsule.
• Insect head carrying:
- sense organs (Antennae)
- compaound eyes and ocelli.
Rigidity of head
• Head is continously sclerotized capsule with
no outward appearance of segmentation, but
it is marked by a number of grooves known as
• The sulci are variable in position in different
species, and some of them may be completely
• Sulcus: impressed line separating sclerites.
• Suture: is the groove marking the boundaries
Rigidity of head con…
• The need of culci for strengthening the head.
• Examples of sulci:
- Epistomal (frontoclypeal) sulcus.
- Subocular sulcus.
- Circumocular sulcu.
- Circumantennal sulcu.
• The sulci defined into different areas:
Rigidity of head Con…
- The Front of the head, the frontoclypeal area
is divided by the epistomal sulcus (fronto-
clyeleal sulcus) into the frons above and the
clypeus below (both attached to variable
muscles run into the pharynx, labrum,
hypopharynx and cibarium).
- Dorsally the frons contenious into the vertex
which separated from the occiput by the
Rigidity of head Con…
• The lateral area of the head beneath the eyes
is called the gena, from which the subgena is
cut off below by the subgenal sulcus.
• The region of the subgena above the mandible
is called the pleurostoma and that part behind
the mandible is the hypostoma.
Rigidity of head Con…
• In all insects the rigidity of the head is
increased by four deep cuticular invagination,
known as apodemes, which usually meet
internally to form a brace for the head and for
the attachment of muscle. The structure
formed by these invagination called tentorium
- internal support for the head capsule
Cut away view of the head capsule
1- Hypogantous: If the head is oriented so that the
mouthparts lie ventrally. In this position mouthparts
directed downward toward the ground
2- Prognathous: If head is directed anteriorly. In some
insects, especially those that pursue their prey or use
their mouthparts in burrowing the mouthparts are
directed anteriorly in front of the insect.
3- Opisthognathos: mouthparts are directed
posteroventral in position. So mouthparts are
directed backward below the insect's body
• All insects posses a pair of antennae, but they
maybe greatly reduced, especially in larval
• Antennal structure
Each antenna consists of :
1 - Basal scape. It is inserted into a
membranous region of the head wall and
pivoted on a single marginal point, the
antennnifear so it is free to move in all
3- Flagellum. It is divided into a number of
similar annuli joined to each other by
membranes, so the flagellum as a whole is
flexible. The number of annuli varies
considerably depending on the species and
• The antennae are moved by levator and
depressor muscle inserted into the scape, and
by flexor and extensor muscles arising in the
scape and inserted into the pedicel.
• There are no muscle in the flagellum (in the
anullated type of antennae ex: locust,
• In Collembola and Diptera, there is intrinsic
musclature in each unit of the flagellum.
• The antennae are primarily sensory structure and
they are rich with sensilla in most insects.
• It is characteristics of insects that the pedicel
contains a chordotonal organ (Johnstons organ),
which respond to movement of the flagellum with
respect to the pedicel.
• Both scape and pedicel have hair plates and a group
of campaniform sensilla that provide information on
the positions of the basal segment with respect to
the head and to each other.
Antennal sensillae Con…
• Scattered mechanoreceptor hairs are also present on
• The principle of sensilla on the flagellum of many
insect are olfactory, and these have a variety of
forms. It is common to contact chemoreceptors,
mechanorecpetor and thermoreceptor.
• Some time the sensilla are concentrated in particular
region of the flagellum ex: in Lepidotera, most
sensilla are aggregated in terminal club.
Function of flagellum
1- It act as sense organ (mainly olfactory), sometime
tactile function. Johnstons organ is important in
regulation of air speed in flying insect. Some time in
female Drosophila and honey bee workers,
perception of near-field sounds.
2- Formation of air funnel (water beetles)
3- In newly hatched form Hydrophilus, the antenna is
facilitated with a number of sharp spines on the
inside of the antenna, assist the mandible in
masticating the prey.
Function of flagellum Con….
4- In fleas and Collembola, the antennae are
used in mating (male used inner surfac bear
large number of adhesive discs with a gland
secreting adhesive material)
Aristate antennae Setaceous
Shore fly antennae
Capitate antennae Lamellate or
Speckled wood clubbed antennae
Clavate antennae Moniliform
Carrion beetle antennae
Plumose antennae Serrate antennae
Male mosquito Click beetle
Filiform antennae Pectinate antennae
Longhorn beetle Firefly
• Insect mouthparts presents in two forms:
- Endognathous (where m.p. lie in cavity of head
produced by the gena. ex: Collembola, Diplura and
- Ectognathous: This form of m.p. is related to diet,
but two basic types can be recognized, one adapting
for biting and chewing solid food, and the other
adapted for sucking up fluids.
This form of m.p. is consists of :
1- Labrum: is a broad lobe suspended from
clypeus in front of the mouth and forming the
upper lip. On its inner side it is membranous.
Different use of muscles can produce a lateral
rocking movement of the labrum. It contains
2- Mandibles: It is rotated about its articulation
by anterior and posterior muscles arising from
the head. It is short, strongly sclerotized, and
the cuticle of the casps is often hardend by
the presence of zinc or manganese.
3- Maxillae: Occupy a lateral position, one on each
side of the head behind the mandibles. The proximal
part consists of
a- Basal cardo, which has a single articulation with the head.
b- Flat plat, the stipes, hinged to the cardo, both are capable of
• Distally on the stipes are two lobes (one or both maybe
a- Inner lacinea.
b- Outer galea.
c- More laterally on the stipes is a jointed-leg-like palp made
up of a number of segments (maxillary palp).
4- Labium: It is similar in structure to maxillae, but
with the appendages of the two sides fused in
the midline so forming a median plate. The basal
part is called postmentum, then is the
prementum which close the pre-oral cavity from
behind. Terminally it bears four lobes, two inner
glossae and two outer paraglossae. Which are
collectively known as ligula. A palp arises from
each side of the prementum, often being three
can be fused to
5- Hypopharynx: is a median lobe immediately
behind the mouth. The salivary duct usually
opens behind it, between it and the labium.
Most of it is membranous, but the dorsal face
is sclerotized distally.
Carpenter ant Stag Beetle Caterpillar
Cockroach Damselfly eating mosquito Termite
Sensilla on mouthparts
• Most senilla on m.p. contact chemo-receptors, but
mechanoreceptors are also common and olfactory
sensilla are often present on the chordotonal organs.
Probably function as pressure receptors, are present
at the tips of mandibular cusps and also in the
lacinea where this is heavily sclerotized.
• The neck is a membranous region which gives
freedom of movment to the head. It extends
from the post-occiput at the back of the head
to the prothorax.
• Latteraly to the neck membrane are the
cervical sclerites (1-3) where muscles are
attached to move the head
Describe the different types of sensilla
that presents on both antenna and