This document provides an overview of the course ZOO 305: Basic Entomology at Lagos State University. It discusses the definition and content of entomology as the study of insect biology, ecology, and importance. The course will cover the external features of insects including the head, thorax, abdomen, wings, and legs. It will also examine insect orders, ecology, population dynamics, and economic importance. The document uses the American cockroach as a model to describe insect morphology and external anatomy in detail over several pages.

1. Lagos State University, Faculty of Science
Department of Zoology and Environmental Biology
ZOO 305: BASIC ENTOMOLOGY (3 UNITS)
2016/2017 SESSION
EXTERNAL FEATURES OF INSECTS
The Team:
Abiodun A. Denloye, Ph. D ; Oyindamola Alafia,
Ph. D; Oluwakemi Ajelara, M. Sc.
1

2. DEFINITION AND CONTENT
• Entomology is the science that studies the
biology (structure & function), Ecology and
importance of insects.
– Structure and function (morphology, physiology,
genetics & ecology).
– Ecology (the study of the interrelationships
between insects and themselves as well as other
organisms relative to their environment).
– Economic importance
2

3. Content:
Diagnostic features of insects. Evolution and taxonomy of insects. Insect
orders. Insect ecology and distribution; population dynamics, sampling
methods and equipment. Economic importance of insects.
• Distribution
• Diagnostic features of insects. Evolution and taxonomy of
insects – Denloye (1st
– 3rd
wk)
• Insect orders - Alafia (4th
– 6th
wk)
• Insect ecology and distribution; population dynamics,
sampling methods and equipment – Denloye (7th
– 9th
wk)
• Economic importance of insects – Ajelara. (10th
– 11th
wk)
3

4. Diagnostic features of insects
• There many species (800, 0000 of insects but one basic body
plan.
The Model: The American Cockroach (Periplaneta americana)
• Why?
• 1. It is a large insect – Large size enables good view of various
external structures and internal organs
• 2. It is a common insect – Commonness makes it available for
studies
• 3. It is important in public hygiene – It would highlight the
role of insects in human societies
4

5. Plate 1: Dorsal view of adult American Cockroach ( Periplaneta americana)
It is such a common insect in Nigeria that it can be found in every house in Nigeria
5

6. • Invertebrates with hard chitinous exoskeleton
• Body divided into three tagmata
– Head
– Thorax
– Abdomen
• Three pairs of jointed legs
– Pro-thoracic legs
– Meso-thoracic legs
– Meta-thoracic legs
• Two pairs of wings (in Pterygote insects)
– Fore-wings
– Hind wings
6

7. Plate 2: Diagrammatic ventral view of adult female P. americana
Notice the external features of insects in the diagram
7

8. Three tagmata – The head
• It is anterior and the first tagma in the insect body
• It is made of a fusion of the prostomium with 6 – 7 post oral segments
• The fused segments bear appendages which are modified into the
mouthparts and serve as organ of food ingestion.
• The head is therefore important to the insect itself and to Man. Why?
• Basic Composition
– Cranium a.k.a head capsule (this is a hardened structure)
– Antennae (a pair) – sensory
– Eyes (simple and compound) - Sensory
– Mouthparts – Oral
Attachment to the Thorax
The head is attached to the thorax by means of a membranous region
called the cervix (the neck)
8

9. The head
The head is a fusion of the
prostomium with 6 – 7
segments
It is normally a capsule
with a sclerotized upper
portion protecting the
brain and a membranous
floor in which is situated
the oral opening or mouth.
9

10. Plate 4: Frontal section
of insect head
The head bears:
1.Simple eyes (Ocelli)
Compound eyes
2.Antennae (One pair)
3.Mouth parts
Parts and funtions
The Frons: The upper-mid
portion of an insects face. It is
that area of the face below the
top two 'ocelli‘. it supports the
'pharyngeal dilator' muscles.
The 'clypeus' is the area of the
face immediately below the
frons . It supports the 'cibarial
dilator' muscles
The 'labrum' is equivalent to
the insect's upper lip ,
The vertex: This is the
remaining part of the insect
face.
10

11. Plate 5: Side view
of insect head
The head bears:
1.Simple eyes (Ocelli)
Compound
eyes
2.Antennae (One pair)
3. Mouth parts
Parts and functions
Gena: This is the side of
the insect head.
11

12. Plate 7: Compound Eyes
(Drosophila melanogaster)
Compound eyes are commonly found
in arthropods
A compound eye consists of hundreds
or thousands of tiny lens-capped
optical units called ommatidia.
Each ommatidium has its own
1.Cornea,
2.Lens
3.photoreceptor cells for
distinguishing brightness and color.
Each ommatidium guide light through
a lens and cone into a channel, known
as a rhabdom, which contains light-
sensitive cells. These are connected to
optical nerve cells to produce the
image.
12

13. Plate 8: Compound eye of mosquito
13

14. Two types of compound eyes
A. Apposition Compound Eye
• Each ommatidium focuses
only rays that are almost
parallel to its long axis, so
that each forms an image of
only a very small part of the
visual field.
• The image of the whole
results from a combination
of these part images.
• Possessed by diurnal insects
B. Superposition Compound Eye
• The sensory cells of an
ommatidium picks up light
from a large part of the
visual field so that the image
received overlaps those
received by as many as 30
neighbouring ommatidia.
• Image gains in brightness but
loses in sharpness compared
with the apposition image
• Possessed by nocturnal
insects
14

15. More facts to note on compound eyes
• Compound eyes generally allow only a short
range of vision. eg, flies and mosquitoes can
see only a few millimeters in front of them
with any degree of resolution, although within
this short range they can see detail that we
could see only with a microscope.
15

16. Plate 9: Dragonfly
Dragonflies have one of the most elaborate eyes of any insect,
capable of pinpointing the motion of a small prey insect several
meters away, even his while the dragonfly is traveling fast. Each
compound eye of dragonflies has 30,000 ommatidia.
16

17. Plate 10: A Monarch butterfly
Butterflies have color vision that is more
enhanced than our own, enabling them to locate
food from flowers.
17

18. Plate 11: American cockroach
Each compound eye of the
cockroach has 2000 ommatidia.
18

19. Plate 11: A typical
antennae
They are a pair of movable segmented
appendages usually situated between
the eyes
The function is largely to perceive
chemical stimuli.
They are extremely varied in shape
and numbers of segments and are
important diagnostic features.
19

20. Plate 12: Modifications of
insect antennae
1. Filiform e.g Cockraoches and
grashoppers
2. Moniliform e.g wrinkeled bark
beetle
3. Clavate e.g Carrion beetle
4. Serrate e.g Click beetle
5. Pectinate e.g fire colored beetle
6. Flaballate e.g Cedar beetle
7. Geniculate e.g Honey bee
8. Plumose e.g male mosquito
9. Aristate eg. Flesh fly
10. Stylate e.g Horse fly
For more follow this link:
http://bugs.bio.usyd.edu.au/learning/resources/Entomology/externalMorphology/antennaTypes.html
20

21. Plate 12: Insect
Mouthparts
The typical mouthpart of
the insect is the chewing
type as shown in the plate
12 on the right
It consists of:
1.Clypeus
2.Labrum
3.Labium
4.Mandible
5.Maxillae
6.Hypopharynx
21

22. Plate 13: Illustrations of typical mouthparts of insects
22

23. Modification of mouthparts
• Piercing-sucking type. The mouthparts of aphids, cicadas, leaf-hoppers,
scale insects and others are modified to pierce their plant host and suck
juices from it. Predaceous insects like assassin bugs, and bloodsucking
insects such as mosquitoes are similarly modified.
• Siphoning tube type. Adult moths and butterflies feed on nectar and
other liquids sucked up through a long proboscis.
• Cutting-sponging type. The mouthparts of many flies are modified to cut
an opening into tissue and sponge up the fluid.
• Chewing-lapping type. Bees and wasps have mouthparts which permit
chewing and tearing of tissue; the fluid material is "lapped up".
• Lapping and Sponging: Houseflies liquify their food and then lap it up.
23

24. Plate 14: Mouthparts of
Honey Bee
24

25. Hypognathous: Mouthparts hang ventrally from
the head capsule . This is the commonest
orientation among plant feeders with chewing
mouthparts .
Prognathous: Mouthparts positioned anteriorly
to the head capsule. This is commonest among
predatory insects.
Opisthognathous: Mouthparts positioned
ventroposteriorly (rearwards) relative to the
head capsule.
(a) hinged, so that they can be swung forwards;
commonest among predators with piercing-
sucking mouthparts, and (b) fixed, commonest
among plant feeders with piercing-sucking
mouthparts.
25

26. The thorax
• The insect thorax consists of three segments
– Prothorax
– Mesothorax
– Metathorax
• Each thoracic segment has four sclerites (Plates).
Each segment bears one pair of wings
In mature pterygote insects each of the mesothorax
and metathorax bear a pair of wings
The mesothorax and metathorax bear one pair of
spiracles each.
26

27. Plate 15: Transverse
Section of Insect thorax
The insect thorax is a box-like
structure.
It is made up of four sclerites
(i.e cuticular plates) namely
1.Notum/tergum (Dorsal
plate)
2.Sternum (Ventral plate)
3.Pleuron (2 nos) (Lateral)
The sclerites play important
roles in the locomotion of the
insect.
27

28. The Leg of Insects
Plate 16 : A typical Insect Leg
Mainly of six sections viz:
1.Coxa - the most basal section of the
insect leg ; articulates with the 'sternites'.
2.Trochanter - joint between the 'coxa'
and the 'femur‘
3.Femur - long and stouter than the other
segments and contains the main muscles
used in running, jumping and digging
4.Tibia - generally long; increases the
length of the leg; adds an extra joint and
thus extra flexibility & the underside of
the tarsal segments may possess pads.
5.Tarsus - consists of 1 – 5 segments.
Serves as the foot of the insect leg.
6.Claws - at the end of the 'tarsus' and
assist the insect in holding onto the
substrate or to its prey. May possess
“arolium”
28

29. Plate 17: Clockwise from Top left - Variegated Grasshopper, Zonocerus
variegatus, Paper wasp, Polistes fuscatus; Common Housefly , Musca
domestica; and Rhinocerus beetle, Oryctes rhinoceros . Centre – American
Cockroach, Periplaneta americana.
29

30. Plate 18:
Cursorial (Running) – e.g
Coleoptera: Cicindelidae such as the
tiger beetle, a voracious predator. It
chases down its prey, much like the
tiger after which it is named. The long
reach of the leg allows it to move so
quickly and results from the long
femur and tibia. Even the tarsal
segments have lengthened.
30

31. Plate 19: Raptorial legs of
a giant water bug (Top)
and a Praying Mantis
(Bottom)
Raptorial: This is for grasping prey.
Egs
1. Hemiptera: Belostomatidae
The giant water bug (Lethocerus
americanus) is a ferocious predator . It
traps its prey using the large raptorial
prothoracic legs. The femur and tibia
form a pincer-like grip. Once the prey is
immobilized it sucks out the fluids of
the haemocoel of the prey .
2. Mantodea: Mantoidea
The classic example of raptorial legs is
the prothoracic leg of the preying
mantid. (Mantis religiosa) . The reach
of the pincer-like tibia and femur is
extended by elongation of the coxa.
31

32. Plate 20: Praying Mantis
(Mantis religiosa)
32

33. Plate 21: Natatorial legs of the giant water
bug (Top), Whirlgig beetle (Middle) and
Diving beetle (Bottom)
Natatorial (Swimming) legs
Hemiptera: Belostomatidae
In addition to its raptorial prothoracic legs, the mesothoracic
and metathoracic legs of the giant water bug are modified
for swimming.
The inner and outer surfaces are lined with a fringe of setal
hairs. Which fold out during the power stroke, and back
during the during the recovery stroke
Coleoptera: Gyrinidae
These beetles get their name, whirligig beetles, from the way
they swim, spinning around and then shooting off in one
direction. Instead of using setal hairs, the mesothoracic and
metathoracic legs have been modified as paddles that scull in
the water to create the propulsive force.
Coleoptera: Dytiscidae
Diving beetles swim using hind legs that are fringed with
setal hairs. They move their legs in a manner similar to
rowing. During the power stroke the hairs increase the
surface area and fold back on the recovery stroke .
33

34. Plate 22: A mole cricket
(Gryllotalpa gryllotalpa)and its
prothoracic leg
Fossorial (Digging)
Orthoptera: Gryllotalpidae
The prothoracic legs of the mole
cricket are modified for burrowing
(fossorial), the modification is when
you compare them to the
mesothoracic legs . Mole crickets dig
and burrow in soft, moist soils.
Key to lower plate: ta = Tarsus, ti =
Tibia, fe = Femur, tr = Trochanter, co =
Coxa.
34

35. Plate 23: Saltatorial legs of
grasshoppers (Top) and Flea
(Bottom)
Saltatorial (Jumping)
Orthoptera: Acrididae
Grasshoppers and crickets have the
classic example of the sartorial
jumping leg. When the muscles in the
femur contract, the joint between the
femur and tibia straightens, and the
hopper is launched into the air.
Siphonaptera: Pulicidae
Fleas are also excellent jumpers, and
when at rest the coxa, femur, and tibia
are all folded against each other.
When they jump, the legs straighten,
and the rapid increase in length lifts
the flea up and off the ground
35

36. Plate 24: Honey bee leg
Odds 'n ends
Hymenoptera: Apidae
The metathoracic leg of the honey bee
is modified for gathering pollen. The
first tarsal segment is very large, and
students often confuse it with the
tibia. The shape of the tibia and setal
hair form a pollen basket. Pollen is
packed into the basket by the spine of
cuticle on the first tarsomere and is
indicated by the pointer.
36

37. The Wings
• Insects are the only invertebrates with wings.
• Insect wings are adult outgrowths of the insect exoskeleton that enable them to
fly.
• Wings are found on the
Mesothorax (Fore wings) (Protects the hind wings)
Metathorax (Hind wings) (For flight)
Fully functional wings are present only in the adults.
Only Pterygote insects possess wings but some lose the wings e.g lice and fleas.
The wings may be present in only one sex (often the male) in some groups such as
velvet ants and strepsiptera, or selectively lost in "workers" of social insects such
as termites and ants.
In some cases, wings are produced only at particular times in the life cycle, such as in
the dispersal phase of aphids.
37

38. Plate 25
38

39. Plate 26: A typical Insect
wing
39

40. Plate 27: Insect Abdomen
It is the third functional tagma
of the insect body
Each segment of the
abdomen consists of
- a dorsal sclerite called the
tergum -
a ventral sclerite, the
sternum
Pleural membrane which
joins the sclerites
.
40

41. Features of the abdomen
• 1. Spiracles: Respiratory openings. On each of the first eight segmentS
• 2. Anus: Rear opening of the digestive tract. Sandwiched between three
sclerites namely a dorsal epicropt and a pair of paraproct.
• 3. Genital openings: Found just below the anus. Surrounded by
specialized sclerites that form the external genitalia (GO). In males, the
GO is usually enclosed in a tube-like aedeagus which functions as the
Penis.
• 4. Pincers -- In earwigs (Dermaptera), the cerci are heavily sclerotized and
look like forceps. Used for defense, courtship and in folding the wings.
• 5. Median caudal filament -- a thread-like projection arising from the
center of the last abdominal segment (between the cerci). Found only in
"primitive" orders (e.g. Diplura, Thysanura, Ephemeroptera).
• 6. Sting -- a modified ovipositor, found only in the females of aculeate 41

42. Plate 28: Insect Ovipositor
42

43. More features of the abdomen
7. Abdominal gills -- respiratory organs in the nymphs (naiads) of certain
aquatic insects.
8. Furcula -- the "springtail" jumping organ found in Collembola on the
ventral side of the 5th
segment. A clasp (the tenaculum) on the third
abdominal segment holds the springtail in its "cocked" position.
9. Collophore – This is a fleshy, peg-like structure found in Collembola. It is
located on the ventral side of the 1st
segment. It maintains homeostasis
by regulating absorption of water from the environment.
43

44. Plate 28: Spring tail (Collembola). Notice features of the abdomen
44