Download Mouthparts

Entomology
By Dr. Fan dong
Insecta Characteristics
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Three body regions: the head, thorax, and abdomen.
Each body region has specialized functions.
The head bears the mouthparts, the eyes, antennae, and
other sense organs, and it houses the brain.
The thorax is the locomotory unit bearing the three pair
of legs and the wings.
The abdomen contains many internal organ systems, for
example, the digestive tract, reproductive organs, and
excretory system.
External morphology
Insecta
External morphology
External morphology of a beetle
THE INSECT'S HEAD

The head capsule is a sturdy compartment that houses
the brain, a mouth opening, mouthparts used for
ingestion of food, and major sense organs (including
antennae, compound eyes, and ocelli).
Other insects’ heads
beetles
moth
truefly
mosquitoes
Grasshopper’s head
Lines and grooves in the head capsule

Ecdysial line: coronal suture usually runs along the
midline of the vertex and splits into two frontal sutures as
it extends downward across the front of the head capsule.
 Midcranial
sulcus: Ecdysial line
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Frontoclypeal sulcus： boundary of frons and
clypeus
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Frontogenal sulcus ：compound eye- mandible,
boundary of frons and gena, Orthoptera and Dermaptera
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Ocular sulcus：skeleton around the compound eye sink
inside
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Subgenal sulcus: between frontoclypeal sulcus
and postoccipital sulcus
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Occipital sulcus
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postoccipital sulcus ：
Grasshopper’s head
Region on the insect’s head
Site on the head
Top
Front
Profile
Region name
vertex
Frontoclypeal area
Ocular sclerite
Back
gena
Subgenal area
Occipital area
Postoccipital area
Frons and clypeus
frons
clypeus
vertex
vertex
Insect tentorium-endoskeleton
Dorsal tentorial arms
Posterior tentorial arms
Anterior tentorial arms
Antenna
The insect antenna consists of three kinds of
segment:
 the first proximal segment termed the scape
 the second segment termed the pedicel
 the larger group of similar distal segments
collectively termed the flagellum
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The joints connecting each flagellar segment are
flexible but can only move passively, whereas those
between the scape and the pedicel and between the
head and the scape are supplied with muscles
allowing them to move actively.
Thus, mechanoreceptors on the flagellum make
actual contact with objects


Johnston's organ in pedicel (second segment) of
antenna.
This organ is a collection of sensory cells that detect
movement of the flagellum
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Detection of object position may be computed centrally
when the tactile outputs from the flagellum and the
proprioceptive outputs from mechanoreceptors at the
scape and pedicel are combined in the central nervous
system.
Functions of antenna

As multimodal sensors for monitoring the chemical
and physical environment.
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Chemoreceptors on the antenna are important in
searching for, recognizing and discriminating
appropriate foods, mates and habitats.
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Mechanoreceptors on the antennae play critical roles
in avoiding sudden attacks by predators and in
perceiving physical objects around an animal
The tactile sense from the antennae
may be especially important in nocturnal insects,
which often have to recognize the physical
environment in more-or-less complete darkness.
 A particular behaviour seen in insects is that they
move their antennae in an exploratory fashion during
environmental searching
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This active antennal movement (scanning) may provide
tactile information about the physical environment that
is more effective than the information that could be
obtained by a walking insect with immobile antennae.
Antenna types
Filiform Antennae
Setaceous -- bristle-like
Dragonflies
Plumose Antennae
moth
Whorled antenna
Mosquitoes
pectinate：elateridae
Capitate antennae
clavate antennae
Butterflies
Antlion
Moniliform -- bead-like

Termites are generally pale in color and have
antennae that look like small beads in a string.
Serrate -- sawtoothed

pea weevil
Geninculate (elbowed ) antennae
Weevils and Ants
Aristate Antenna: house flies
Lamellate Antenna of Scarab Beetle
Antenna groove (x285)
compound eyes
The compound eyes are often the most prominent
structures on the head of the insects that possess
them, as is shown in the dragonfly below
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
Horse flies (order Diptera) have spectacular
compound eyes
The compound eye is made
up of thousands of sensory
units called ommatidia, each
of which has an hexagonal
lens and 6-8 light sensitive
cells.
Ommatidia of mosquito (x3080)
Each omnatidium has a limited field of view, but sensory
information from adjacent ommatidia combines to allow for
an image to be 'compiled' in the optic lobe of the insect brain
Compound Eye
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In most insects there is one pair of large, prominent
compound eyes.
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It is composed of several units called ommatidia.
There may be up to 30,000 ommatidia in a
compound eye.
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This type of eye gives less resolution than the
vertebrate eye, but it gives acute perception of
movement -important in flight.
ocelli ：When present,
ocelli(either 2 or 3), detect low light
or small changes in light intensity
 The 'simple eye' of many adult insects which
consists of a single bead-like lens.
 Ocelli may also be absent in some insects
ocelli
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It is believed that they help to find the sea-level or
horizontal during flying.
We still not exactly sure their functions.
Compound eyes
and ocelli on
halictid bee (order
Hymenoptera).
Mouthparts
Mouthparts have evolved for special needs for
different insects.
 They can chew, suck, pierce, lap, and sponge-up their
food.
 Grasshopper has the most primitive type of
mouthparts for chewing.
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Basically all other types of mouthparts are evolved
from the chewing type.
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The labrum is suspended from the clypeus and form
the upper lip.
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Their function is to help keep food in the mouth.
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The mandibles are transverse jaws for cutting and
grinding.
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Behind the mandibles there is the maxillae.
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The maxillae also function as a set of jaws for food
manipulation.
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The labium functions as a lower lip.
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Maxillary palpus and labial palpus are used for
touching, tasting, and sensing temperature
Types of mouthparts
Chewing mouthparts
 Chewing –lapping mouthparts
 Sponging mouthparts
 Scratching mouthparts
 Siphoning mouthparts
 Grasping-sucking mouthparts
 Rasping mouthparts
 Piercing- sponging mouthparts
 Piercing- sucking mouthparts
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Chewing mouthparts
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labrum
mandible
maxilla
labrum
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maxilla
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labium
mandible
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hypopharynx
hypopharynx
labium
Generalized Insect Head with
Chewing Type Mouthparts
Labrum
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The labrum is the 'upper lip' of the mouth; it is a broad
plate structure that is an extension of the head.
The labrum helps pull food into the mouth.
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Labium
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The labium is the 'lower lip' of the mouth, made up of a
fused set of jaws and is a true mouthpart (not part of
the head).
The labium also consists of a pair of labial palps.

 Labial
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palps
The labial palps are often covered with sensory hairs
and scales and test whether something is food or not.
 Mandible

The mandibles are a hard pair of jaws, with teeth and
grinding surfaces that work sideways to chew and
grind food.
 Maxillae
The maxillae (singular: maxilla) are the second pair of
jaws with teeth and maxillary palps. The teeth work
sideways, to select and chew food.
Maxillae structure
Cardo
 Stipes
 Galea
 Lacinia
 Maxillary palps
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 Maxillary
palps
The maxillary palps are sensory organs with tiny hairs
and they also have organs of taste and smell.
Hypopharynx
Dense hair on the wall
 Function：
 Sense of taste
 Its muscle can control expand and contract : food
can be delivered and swallowed
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Modifications of Chewing
Mouthparts
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Elongate rostrum of chewing insect (Hollyhock weevil)
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Chewing mouthparts of yellow jacket Wasp
Insects which have chewing mouthparts :

Orthoptera and Coleoptera: adults and larvae
 Neuroptera: adults
 Lepidoptera : larvae

Hymenoptera: most of adults and sawfly larvae
Mouthparts prolong
Piercing Sucking
proboscis
Insect which feed on plant liquid or animal blood
 Mouthparts can pierce into host and absorb its body liquid.
 Hemiptera, Homoptera and some mosquitoes in Diptera
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Mandibles and maxillae are formed into stylets which
are enclosed by the labium.
Once the stylets penetrate, a secretion is injected to
dissolve tissue, act as a toxin in predacious species,
or as anticoagulant for mosquitoes
Piercing Sucking of plant feeders
(True bugs, aphids, scale insects)

Mouthparts are shaped to brace the proboscis (beak)
as the needle like mouthparts (stylets) penetrate the
leaf tissue.
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The head is musculated with a cybarial pump that
helps insect suck plant fluid
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Labrum of cicada reinforces proboscis which is a tube
made of the rolled up labrum(lower lip)
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Mandibular stylets lay curved in the tube and are
used to pierce the plant tissue
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Maxillary stylets are contained within the mandibular
tube and form 2 tube.
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The salivary tube is used to secrete enzymes that
prevent the plant phloem sieve tubes from sealing or
plant tissue from suberizing.
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The food channel is used to suck up the plant fluid.
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Note that some predaceous bugs have a similar
morphology that allows them to skewer insects and
suck out their body fluids.
Piercing sucking blood feeder
(female mosquito)
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Note that the same mouthparts are used to produce
a penetrating proboscis.
Adaptations are to allow continual tissue cutting by
maxillary and mandibular stylets, while a much larger
food canal is used to suck up the blood.
Salivary ducts are key to secreting anticoagulant
enzymes.
Chewing-Lapping mouthparts
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Adult honeybees and bumble bees. Mouthparts are
modified to utilize liquid food, honey and nectar.
A central "tongue" is used to draw liquid into the
body.
The mandibles are not used for feeding but function
to cut floral tissue to gain access to nectar, for
defense, and for manipulating wax.
Rasping mouthparts
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Thrips have rasping mouthparts to scrape foliar
surfaces so they can then consume the fluid exuded
from the damage.
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These insects have an unusual adaptation in that the
mouth has 3 stylets and lacks bilateral symmetry.
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The left mandible is modified into a stylet as well as
the part of each of the maxillae (lacinea).
Siphoning mouthparts
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Moths and butterflies. When feeding the proboscis is
uncoiled and extended.
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Nectar is sucked up into the mouth or oral cavity.
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Note this modification is just for sucking nectar out of
plants, and water out of puddles.
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There is no need to pierce anything.
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The curled tube of the mouth is formed by a
specialized, musculated, part of the maxilla called
the galea.
Sponging mouthparts
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Found in adults of specialized flies. During feeding the
proboscis (modified labium) is lowered and salivary
secretions are pumped onto the food.

The dissolved or suspended food then moves by
capillary action into the pseudotracheae (sponge)
and is ingested.
There may be sharp teeth on the pseudotracheae to
rasp flesh and draw up blood.
 The labella is the fleshy distal end of the labium that
functions as a sponge-like organ to sop up liquids
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Grasping-sucking mouthparts
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Neuroptera : adults and larvae have different kinds
of mouthparts
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Adults : chewing mouthparts
Larvae: grasping-sucking mouthparts
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characteristics:
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long and wide mandible with sharp tip, which is like a sickle
Very small cardo and stipe , developed galea like a fine sickle
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Scratching mouthparts
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Larvae of flies
Degenerative head draws back into prothorax
Degenerative mouthparts, only a pair hooks with which
the larva could scratch food and take the juice and solid
scrap
Mouthpart Orientation
Hypognathous
Hypognathous (Ventral) –Many herbivores
 Grasshoppers, caterpillars, tiger beetles
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Mouthpart Orientation
Prognathous (Anterior) –Many Predators
 Great for predators trying to eat an insect it
catches. lacewing larvae
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Mouthpart Orientation:Opistognathous
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mouthparts directed toward posterior
Some Sucking insects, great for drilling
through wood (Cicada)
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Fixed toward posterior (herbivore)