9/3/2009
Insects and
Human Society
Lecture 3: Insect Anatomy
External Morphology
p gy
Insects are heterotrophic invertebrates w/ an
articulated exoskeleton and 6-legged adults
Living organisms
Kingdom: Animalia
Ph l
Phylum: Arthropoda
A th d
Class: Insecta
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External Anatomy
¾ Study of external anatomy is called Morphology
¾ Morphology is coined by Goethe in 1822 from
the Greek world Morphē (= Form) and the German
world Logie (= study)
¾ Morphology is the branch of biology that deals
with form and structure of animals and plants
¾ External anatomy is important to 1) understand
the functions of the various insect designs and to 2)
allow identification of insects and their relatives
Objectives of Lecture
Describe and discuss the functions of
diff
different
t body
b d parts
t off insects:
i t
¾ Cuticle
¾ Body segmentation
¾ Structure of head, thorax,
abdomen and their appendages
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The cuticle
¾Provides the strong exoskeleton of body (that
serve to give rigid structure & protect
i
internall organs)) andd the
h apodemes
d (internal
(i l
support and attachment point for muscles)
¾Cuticle may range from rigid and armor-like
(adult beetles) to thin and flexible (many
larvae)
¾ Prevention of water loss (desiccation) is a
critical function of the cuticle
¾Key contributor of the success of insect
The cuticle
¾ Cuticle is a thin layer but a complex structure
Epidermis: Single layer that lies beneath and
secretes
t theth cuticle
ti l
Cuticle is composed of the thicker procuticle
overlaid with thin epicuticle
Epidermis and cuticle together form an
integument (or body wall) which is the outer
covering of living tissues of an insect
In between sclerites the body wall is softer –
allows for growth, expansion and movement
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The Body Wall
¾The body wall or integument is composed of a
layer of cells called the epidermis, with the
basement membrane on the inside and the cuticle
on the outside
Procuticle
The body wall-cuticle
• The epicuticle (top layer) prevents water loss,
repels excessive water, deters predation, provides
patterns for mimicry, reflect solar
• The exocuticle gives the cuticle its strength and
resilience and is formed from chitin (also base for
wood, hair, horns)
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The body wall-Pigments
¾Brown and black pigments called melanin are
present in cuticle to give insect color
¾other colors may be possible by other pigments
with clear cuticle or diffraction patterns in cuticle
to give iridescence
Some basic terminology
Rear Front
Top
Bottom
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Segmentation and Tagmosis
¾Arthropod body is composed of several segments
¾Primitive insects were worm-like with many
segments (generally
(generall 20)
¾In today’s insects, segments are grouped into
function units or regions or tagmata -- this
process is called Tagmosis
¾The 20 original segments composing insects are
grouped into 3 regions:
Head (6 segments)
Thorax (3 segments)
Abdomen (11 segments)
• Insect: Derived from the Latin word
“insecticum” meaning ‘cut into’
• Insect body is cut into three parts: Head
(H) Thorax (T) & Abdomen (A)
(H),
A T H
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Primary Functions of Tagmata
¾ Head
Sensory perception
Neural integration
Food gathering and manipulation
¾ Thorax
Locomotion
¾ Abdomen
Houses visceral organs (Digestion,
Reproduction, etc…)
Insect Head
¾Structure
Head is entirely encased in rigid exoskeleton
No sign of segmentation
A t i partt off the
Anterior th head
h d isi the
th frons
f
¾Orientation
Based on the inclination of the long axis of the head compared
to the entire body, there are 3 basic types of orientation
Prognathus: long axis of head horizontal and in line w/ long
axis of insect body
Hypognathus: long axis of head is at right angle (vertical) to
the long axis of insect body
Opisthognathus: long axis of head horizontal, but the tip
end is directed backward and arises between the anterior legs
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Insect Head
• Composed of the cranum, insect head bears eyes
(compound eyes and ocelli), antennae and
mouthparts
p
E
Eyes
Antennae
Frons
Mouthparts
Insect Head -- Eyes (Insect Vision)
¾Compound Eyes
Compound eyes are large and well developed w/ many small
individual facets or ommatidia (ommatidium in singular); has
crystalline
lli lens
l andd light
li h concentrating
i cells
ll
Form a picture of what insects see (light sensitive)
Present in most adult insects but absent from larvae
¾Ocelli (Ocellus)
Simple eyes lack crystalline lens
3 light-sensitive eyes, typically arranged in a triangle are
located in the dark surface on the face of the insect
¾Stemmata (only present on some species)
Simple eyes with crystalline lens located laterally on certain
larvae (holometabolous)
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Insect Head -- Eyes (Insect Vision)
¾Compound Eyes
Insects cannot move or focus their eyes; they have a sharp vision
for only a short distance (less than 1 yard)
they can see a broader range of light rays than people
Insects have no eye lid, their eyes are always open
¾Ocelli
Simple eyes cannot form images
can only tell differences between dark and light
A fly has huge compound eyes that
cover most of
its head
Insect Head -- Antennae
¾ One pair of antennae
Most insects have 2 antennae between their eyes
These antennae are jointed and mobile
Used chiefly to smell and feel (touch)
Some insects use antennae to taste and hear
Antennae can detect humidity changes, vibrations,
wind velocity and direction, chemical cues
Most insects become distress when antennae damaged
or removed and some are helpless
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Insect Head -- Antennae
¾ Antennae vary greatly among insects but all
follow a basic plan w/ 3 main divisions
1. basic segment called scape is generally larger than
the other segments; it is inserted into the insect head
2. the second segment or pedicel follows the scape
contains a sensory organ known as Johnston’s organ
that responds to movement of the distal part of the
antenna
3. the remaining part is the flagellum is often
filamentous w/ multiple segments
¾ Antennae are reduced or almost absent in some larval
insects (e.g. Hymenoptera)
Insect Head -- Antennae
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Insect Head -- Antennae
¾ Numerous variations in the antennae of different insects
Insect Head -- Antennae
• Numerous variations in the antennae of different insects
Type Description Found on
Filiform thread-like field cricket
Setaceous bristle-like cockroach
Capitate head-shaped nitudilid beetle
Clavate tapering club-like butterfly
Lamellate flat plate-like June beetle
Moniliform string of beads termites
Serrate saw toothed click beetle
Geniculate elbowed chalcid
Pectinate comb-like
comb like moth
Plumose with plumes mosquito
Aristate with an arista housefly
Flabellate pile of thick plates cedar beetle
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Insect Head -- Mouthparts
¾ Mouthparts
Group of structures on the lower part of the head that
are adapted to diet
Formed from modified appendages of segments
making the head
¾As insects take many forms and have a wide
range of food types, they also have various
mouthparts that can be grouped into two
main categories:
Mandibulate (chewing)
Haustellate (sucking)
Insect Head -- Mouthparts
1. Mandibulate Mouthparts
Most primitive mouthparts
Adapted to solid diets,
diets these mouthparts are generally
biting and chewing
Composed of five primary parts:
9clypeus
9the upper lip or labrum
92 jaw-like structures or mandibles
9the maxillae (singular maxilla)
9the lower lip or labium
Maxillae and labium are further divided into various
substructures
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Insect Head -- Mouthparts
Insect Head -- Mouthparts
Chewing mouthparts are present in
grasshoppers, crickets, locusts, cockroaches,
beetles caterpillars (larvae of moths and
beetles,
butterflies)
Ground Beetle
Grasshopper Cricket Black swallowtail caterpillar
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Insect Head -- Mouthparts
2. Haustellate Mouthparts
Used primarily for ‘sucking up’ liquids of fluids
from plants and animals
Haustellate mouthparts are divided into 2
groups based on:
9presence or absence of stylet
9stylet
y is a needle-like p projection
j used to penetrate
p
plant or animal tissues
Insect Head -- Mouthparts
¾ Haustellate Mouthparts
Insects w/ stylate MP
have a stylet used to
pierce and pump up
fluids (piercing-
sucking)
Insects with stylet
include aphids,
p ,
leafhopper, flies, fleas,
mosquitoes
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Insect Head -- Mouthparts
¾ Haustellate Mouthparts
Some haustellate
mouthparts lack stylet
Unable to pierce tissue
they must rely on easily
accessible liquid food
such as nectar at the
base of flower
Insects with nonstylate
MP comprise butterflies,
moths which have long
siphoning proboscis
Insect Head -- Mouthparts
¾ Haustellate Mouthparts
Some insects w/haustellate
mouthparts feed on liquid
but also on solid and semi-
solid diet by external
digestion
Solid food is liquefied by
digestive fluids before being
sucked
k d up. These
Th insects
i
have sponging MP
E.g. Housefly
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Insect Head -- Mouthparts
• Haustellate Mouthparts
¾ Some insects
w/haustellate
/h t ll t
mouthparts feed on
liquids but also semi-
solid diet by lapping
¾labium modified into a
hairy tongue
¾ E.g. Honeybee
Insect Head -- Mouthparts
¾ Most common five
mouthparts
p
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Insect Head -- Mouthparts
¾Recognition of the types of mouthparts
Insect Name Mouthpart Plant injury
type
? Chewing Hole in leaves
Aphid ? Removal of
juices
Honey bee Lapping ?
Insect Thorax
¾ Thorax is the locomotor tagma
¾ The thorax of insect consists of 3 segments
prothorax
p (pro = first))
(p
mesothorax (meso = middle)
metathorax (meta = last)
¾ Each segment consists of hardened plates or sclerites
¾ Dorsal sclerite is notum (plural nota), lateral sclerite is
pleuron (plural pleura) and ventral one is sternum (plural
sterna)
¾ Each of the 3 thoracic segment contains one pair of legs
¾ Wings are found only on the meso- and meta-thorax. No
wings on the prothorax
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Insect Thorax
Insect Thorax
Legs
• 3 pairs of legs (6 total)
Fore-legs
Fore legs (2) on the prothorax
mid-legs (2) on the mesothorax
hind-legs (2) on the metathorax
• Each leg has 6 major components
coxa (plur. Coxae)
t h t
trochanter
femur (plur. femora)
tibia (plur. tibiae)
tarsus (plur. tarsi)
pretarsus (plur. pretarsi)
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Insect Thorax
Legs
Femur and Tibia are generally the longest segments
Insect Thorax
¾ Leg modification: Insect legs are modified for adaptation to
various functions
walking (gressorial or ambulatorial) like in field cricket
runningi (cursorial)
( i l) like
lik in
i roaches
h
grasping (raptorial) like in praying mantis
digging (fossorial) like in Gryllotalpa (ground-dwelling insects)
clinging (scansorial) like in fleas
hearing (tympanum) like in prothoracic leg of grasshopper
swimming (natatorial) like in scavenger beetle
jumping (saltarorial) like in hind legs of grasshopper
clasping legs in some males to hold females, e.g. Dytiscus male
making sound (stridulatory organ) like in tettigoniid
collecting food like pollen, e.g. metathoracic leg of bees
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Insect Thorax -- Common types of legs
Insect Thorax
¾Wings
When present, wings arise from the meso- and
metathorax, but many insects are wingless (without wings or
apterygota)
Typically, there are 2 pairs of wings, but in few groups
wings are reduced to one pair (true flies or Diptera)
Wings are mostly membranous but in beetles the forewings
((elytra)
y ) are hard cases and do not take ppart of flight
g
Membranous wings are supported by thickened ribs called
veins
Pattern of arrangement of these veins used in insect
classification
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Insect Thorax
¾Wing regions
Insect Thorax -- Wing Variation
- Elytra for protection
- Halteres: hind wings completely
reduced to mere nubs used for
b l
balance andd direction
di i during
d i flight
fli h
(e.g. true flies)
- In some male insects, sound producing mechanisms (file and scraper)
are present on the underside of forewings and forelegs-- sound used
mating calls (e.g. male grasshopper).
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Insect Abdomen
• Insect abdomen has 11 segments although segment 1 may be
reduced or incorporated into the thorax (e.g. Hymenoptera) and the
last 2 segments are variously modified or diminished
• hard dorsal part of abdomen is tergum (terga) and ventral part is
sternum (sterna)
• Dorsal and ventral plates are joined together by a soft inter-
segmental membranes
• There are small dark openings (spiracles) set into the soft
membranous area, each along side the abdomen-- one pair on each
segmentt
• 2 pairs of spiracles are also present on the thorax
• a pair of cerci of the 11th abdominal segment; cerci permit
sensory pickup from the back
Insect Abdomen
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Insect Abdomen
¾Abdomen hosts major viscera, heart, and
reproductive organs
¾ Reproductive organs are located on the 9th
segment for males (aedegus or penis and often a
pair of claspers) and on the 8th and 9th
abdominal segments for females (external
ggenitalia or copulatory
p y openings
p g and ovipositor
p
for egg laying)
¾In higher Hymenoptera, the ovipositor is modified
to form a poison injecting apparatus, the sting
(wasps, bees) used for defense
Summary of Insect Body
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Study questions
• How many segments can be found on a primitive insect?
• What are the main tagmata of an insect?
• Are there spiracle on a) head?, b) thorax?
• How manyy ocelli are present
p on an insect?
• What is the function of antennae?
• Why are they modifications of insect legs?
• What are the two major groups of insect mouthparts?
• What are the major functions of an insect head and how do these
compare with those of other animal heads?
• Name the major appendages associated with the insect head?
• What is the major function of insect thorax?
• How many segments make up the thoracic region, 20, 11, 9 or 3?
• Are wings found on all stages and all insects?
• What is an ovipositor?
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