This document provides an overview of entomology and arthropods. It defines entomology as the study of insects and their classification. There are several branches of entomology including medical entomology, which deals with insects that affect human and animal health. The document describes the key characteristics of arthropods including their exoskeleton, segmented bodies, and jointed appendages. It outlines the development stages of arthropods from egg to adult and classifies the major groups, including insects, arachnids, and crustaceans. The document also discusses the medical importance of arthropods as disease vectors and outlines common vector-borne parasites.

1. INTRODUCTION
• Entomology (en-toe-mol-o-gee)is from the Greek word entomo,
meaning insect.
• Entomology: It is a science that deals with the study of arthropods
in general, and incorporates sciences like zoology, biology,
parasitology and micro-biology.
• Medical entomology This is a branch of entomology which deals
with arthropods which affect the health and well-being of man
and vertebrate animals.
• In other words, medical entomology is the medical science directly
concerned with vectors that affect human and animal health.
• Of an estimated 5–10 million species of insects, probably not more
than a fraction of 1% interact, directly or indirectly, with humans.

2. Entomology
There are also other branches of entomology for
example:
• Industrial Entomology/ Economical Entomology:
deals with industrially or economically important
arthropods (industrial pests).
• Agricultural Entomology: Agricultural pest science
dealing with arthropods that affect plants and
animals.

3. INTRODUCTION
• Arthropods: “Arthro” means jointed and
“Poda” means legs.
• Arthropods are invertebrate animals with
jointed-legs and identified by their peculiar
characteristics.
• Entomologist the scientist who specializes in
studying insect life.

4. DEVELOPMENT OF ARTHROPODS
DEVELOPMENT OF ARTHROPODS
The development of arthropods, which is called
metamorphosis, is from egg to adult.
 Metamorphosis: drastic change in shape & form for growth and
development.
 Tow types :
 Incomplete : development from the egg to nymph, which
looks like the adult
 Complete : development, which extends from the egg to
larva, pupa that later differentiate to the adult arthropod.
 The stage of developing of an insect will affect insecticide
efficacy.

7. Insects growth
Insects need to shed
(molt) an old skin to
grow in size.
The period between
molts of larvae called an
Instar.
Most insects have 4- 8
instars before becoming
adult.

8. Arthropods
• All arthropods, while varying considerably in size and shape, have
certain features in common .
• They are all bilaterally symmetrical and metamerically segmented.
• They have a hard chitinous exoskeleton, sometimes sclerotized or
calcified.
• Inside which is a hollow blood cavity containing a clear fluid
(haemolymph), a dorsal tubular heart.
• Alimentary tract.
• central nervous system of two longitudinal nerve trunks fused
segmentally to form ganglia.
• Respiration may be achieved by a variety of methods: via gills, lung-
hooks, gaseous exchange through the cuticle or by means of
spiracles.
• All arthropods have jointed appendages, which may take the form
of legs, antennae, mouthparts or cerci.
• The sexes are always separate.

9. Beneficial Effects of Insects
1- Insects pollinate flowers hence, fruit formation depends on them.
2- Insects form a source of food for man e.g. honey, termites, caterpillar.
3- Useful materials such as silk, bee wax, etc are obtained from insects
4- Insects are important in food chains, e.g. Aquatic insects form food for
the fishes
5- Insects are important as scavengers – (decomposition involving cycling
of materials)
6- Insects are important tools, e.g. Drosophila is used for research in
genetics, physiology etc.
7- Some insects are used to control others that are pests (Biological
Control)
8- Insects have aesthetic value (e.g. Butterflies are collected for their
beauty).
9- Myiasis, the infestation of animal tissues (living or dead).

10. IMPORTANCE OF ARTHROPODS IN PARASITOLOGY
Arthropods affect the health of man by being:
(a) Direct agents for disease /discomfort.
The following effects may be seen by the direct effect of arthropods.
• Annoyance – comes from disruptive activities of insects, such as
flying around or landing on the head, and from feeding, possibly causing
blood loss, though they don’t remove sufficient blood to cause a
medical problem in humans.
• Entomophobia – is an irrational fear of insects. One extreme form of
entomophobia is delusory parasitosis, in which individuals become
convinced that they are infested with insects when no actual infestation
exists.
This may cause undue alarm and anxiety, leading to unwarranted use of
insecticides, and in severe cases, requiring professional treatment.

11. IMPORTANCE OF ARTHROPODS IN
PARASITOLOGY
• Envenomization – is the introduction of a poison into the body of
humans and animals. Arthropods may also inoculate poison to the
host. E.g. Scorpion
• Allergic reactions – a hypersensitive response to insect proteins.
All of the mechanisms associated with envenomization can also cause
exposure to allergens. In fact, human deaths from bee and wasp stings
usually are associated with a hypersensitive reaction rather than direct
effect of a toxin.
• Dermatosis and dermatitis – dermatosis is a disease of the skin and
dermatitis is an inflammation of the skin. Both dermatosis and
dermatitis can be caused by arthropod activities.
Many mite species, such as scabies mites produce acute skin irritations

12. Arthropods affect the health of man by being
(b) Agents for disease transmission
Arthropods can carry disease causative agents in the following two ways.
• Mechanical carrier
Here they lodge the disease causative agent without altering its development or
multiplication.
1- Direct Mechanical carrier :
- disease agents are carried from one host to another by inoculation arthropods
simply mechanically carried.
2- Indirect Mechanical carrier: In this type of disease transmission by the body parts
(example wings, hairs, etc). simply deposited in the body, food or drink of the host
e.g. house fly.
• Biological carrier
When arthropods become biological carriers for transmission of disease, it means that
certain stages in the life cycle of parasite takes place in the body of the insect.
e.g. Anopheles mosquitoes.

13. Types of biological carrier
􀂃 Propagative- where there is multiplication of the parasite
with no developmental change .
e.g. Yellow fever virus in Aedes mosquito.
􀂃 Cyclopropagative – in this type both multiplication and
developmental change are going on.
e.g. Plasmodium species in Anopheles mosquito
􀂃 Cyclodevelopmental – here there is developmental change
of the parasite but no multiplication
E.g. Wucherera bancrofiti in Culex mosquito
􀂃 Transovarian- when the parasite passes to progeny
arthropods through the ova.
E.g. Rickettsia typhi in ticks

14. Vector-borne Parasites
 A vector: is an agent(arthropods) which
transfers a parasite from one host to another.
 Typical parasite vectors: fleas, ticks, mites,
mosquitoes, flies, and other insects.
A zoonotic disease: is any disease which may be
passed from animals to people or from people
to animals.

15. Arthropod Habitats
Arthropod Habitats
• Depending upon species, arthropods live in
various habitats.
• The following are some of the factors that
control habitats of arthropods: food, disease,
breeding media, climate, competition, natural
enemies and etc.
• The habitats of arthropod include soil, water,
ambient air, man, animal and plants.

17. CLASSIFICATION OF ARTHROPODS

18. CLASSIFICATION OF ARTHROPODS
There are three medically important classes of
Arthropods:
1. Class Insecta- (Hexapoda) consists of
mosquitoes, fleas, bugs, flies, etc.
2. Class Arachnida- (Octapoda)consists of ticks,
mites , scorpion, etc.
3. Class Crustacea- consists of Cyclops, crabs,
cray fish, etc.

19. 1. Class Insecta
The general feature of this class includes:
• Division of body into head, thorax and
abdomen.
• Possess one pair of antenna on the head.
Antenna (pl., antennae)—A segmented organ
located on the head, usually used for smell.
• 3 pairs of legs, carried by thorax.
• Wings may be present and could be one /two
pairs.

20. Insect anatomy
• The following characteristics are useful in
comparing insects with other animals:
• Three body regions.
• Wings.
• Legs.
• Antennae.
• Mouthparts.

21. Three body regions
• An adult insect’s body is made up of three parts:
- Head.
- Thorax .
- Abdomen .
However, the division between thorax and abdomen is not always
obvious.
• The thorax is made up of three segments: prothorax, mesothorax
and metathorax. Each of these segments bears a pair of legs. The
wings are attached to the mesothorax and/or metathorax, never to
the prothorax (first segment).
• The abdomen usually has 11 or 12 segments (although some insects
have fewer), but in many cases they are difficult to distinguish.
Some insects have a pair of appendages (cerci) at the tip of the
abdomen. They may be short, as in grasshoppers, termites and
cockroaches; extremely long, as in mayflies; or curved, as in
earwigs.

22. Wings
 Insects are the only flying invertebrates.
• - Most adult insects have one or two pairs of wings. Some, however, have no
wings.
- Wing function for flight varies among insects.
• - Wing surfaces may be covered with fine hairs or scales, or they may be bare.
• The thickened front wings of beetles serve as protective covering for the hind
wings when the beetle is not flying.
• The membranous hind wings are the actual flight mechanisms.
• Venation (the arrangement of veins in the wings) is different for each group of
insects thus, it serves as a means of identification. Often wing venation is
common to all members of a family or genus. There are systems for
designating types of venation for descriptive purposes.
• The names of most insect orders end in “ptera,” which comes from the Greek
word meaning wing. Thus, each name denotes some feature of the wings.
Hemiptera means half-winged; Hymenoptera means membrane-winged;
Diptera means two-winged, and so forth.

25. Legs
• Another important characteristic of insects is the presence of three
pairs of jointed legs on the thorax.
• These legs almost always are present in adult or mature insects and
generally are present in other stages as well.
• Uses of legs : - To walking.
- Jumping.
- Insects often use their legs for digging.
- Grasping, Feeling, swimming, carrying loads,
building nests and cleaning themselves.
Because insect legs vary so greatly in size and form, they are
regularly used in classification, especially the extreme part of the leg
(the feet, or tarsi).
• Prolegs (fleshy body projections or false legs) occur only on larvae
of certain insect orders. They are used for clinging to plants.

26. Antennae
• One of the main features of an insect’s head are
its antennae.
• All adult insects (except, at times, scale insects)
have one pair.
• They usually are located between or in front of
the eyes.
• Antennae are segmented, vary greatly in form
and complexity and often are referred to as horns
or feelers, which is misleading.
• They primarily are organs of smell, but serve
other functions in some insects.

27. Mouthparts
• Mouthparts:
- The most remarkable structural feature of insects,
and the most complicated.
- Vary in form and function.
- Two basic types: chewing and sucking.
- There also are intermediate types of mouthparts:
1- chewing-lapping (found in honeybees,
wasps and bumblebees).
2- Rasping-sucking (found in thrips).
-Some insects have different mouthparts as larvae and adults.
Larvae generally have chewing-type mouthparts regardless of
the kind they’ll have as adults. Nymphs have mouthparts
similar to those of adults. For some adult insects, the
mouthparts are vestigial (no longer used).

28. Type 1: Chewing Mouthparts
• Four basic parts.
• Mandibles used for
chewing.
• More primitive and
generally stronger than
sucking types.
• Cannot feed on liquids
materials.

29. Type 3 : Siphoning(coiled) mouthparts
 Only proboscis or coiled
tub are present.
 Short lived as adults,
feed intermittently.
 Vary greatly.
• Example: butterflies,
moths.

30. Type 4: Sponging mouthparts
 Reduced mouthparts
suitable for soaking up
liquids.
 No ability to eat solid
foods.
 Some flies can bite but
is actually scratching to
feed on blood.
 Example: flies (house
fly)

31. Type 5: Piercing and sucking MP.
 All mouthparts shaped
like needles that form
feeding tubes.
 Only female of
mosquitoes are bite.
 Example : mosquitoes
(6needls), plant bugs(4
needles)

32. Type 2: Chewing lapping mouthparts
Complex modification of MP.
 Mandible used for
chewing.
 Proboscis used for
drinking (lapping) and
exchanging fluids.
 Mouthparts allow
molding wax, feeding on
pollen, nectar.
 Examples: Honey bee,
wasps.

36. Classification
• The anatomy of an insect places it into a specific
insect group called an order Each order is
divided into families family
genera and finally species. A specific insect
usually is described by genus and species names;
e.g., Musca domestica is the common housefly.
• To categorize insects, professionals observe
differences in body parts through a microscope.
• Gardeners generally classify insects by common
name.

37. Class Insecta/Hexapoda
 Class Insecta/Hexapoda (the six legers).
• The insects (class insecta) are the most abundant species.
• In fact, about . million species are known, i.e. about 75% of all arthropods are
insects.
• They are the greatest pest animals as well and the greatest animals of medical
importance (lots of diseases are transmitted through insects).
• The body parts of insects are grouped into three: head, thorax and abdomen.
• The head contains eyes, one pair of antennae and three pairs of appendages
developed as mouth parts (details are discussed in chapter four).
• The thorax has three pairs of legs, and one or two pairs of wings in most insects
(some insects have no wings).
• The abdomen is segmented with the end (posterior) part serving to show the
sex of the insect.
• A “V” shaped abdomen helps for egg disposing, carrying the genital and
excretory organs. The abdomen also contains diffusion tubes called spiracles
for air exchange (respiratory organs).

38. Class Crustacea
• Class Crustacea - Cyclops, the sea- food group such as lobsters,
crabs, cry fish, etc
• The crustacean has evolved a two fold division of the body into a
cephalothrax means prosoma (head and chest) and opisthosoma
means abdomen .
• The former bears sensory organs and mouth parts to form the head
region and also five pairs of enlarged appendages for walking (in
the higher forms).
• The crustaceans have two pairs of antennae.
• The prosoma carries the main sense organs (internally and
externally) that is the antennae, the eyes and the feeding parts.
• Opisthosoma consist the spiracles (respiratory organs) and the sex
organs

39. Class Arachnida
• Class Arachnida(the eight legers) - Spiders, mites,
ticks, scorpions etc.
• The class Arachnida has four pairs of legs.
• The head and the thorax are fused forming a
cephalo-thorax.
• The appendages (legs) are located on the
cephalothorax.
• The head has no antennae, but pedipalps and
different mouth parts from that of insects.

40. `
Crustica
Archanida
Insecta
Characteristics
Body divided into
cephalothorax and
abdomen
Body divided into
cephalothorax (head
and thorax fused) and
abdomen
• Division of body into
head, thorax and
abdomen
Body
Octapoda :4 pairs of
legs
Octapoda :Possess 4
pairs of legs
Hexapoda :3 pairs of
legs, carried by thorax
Legs
2 pairs of antenna
No antennae
Possess one pair of
antenna on the head
Antennae
Wingless
wingless
Wings one /two pairs
(sometimes absent).
Wings
`
`
- Complete.
- Incomplete.
Life cycle
includes the
Cyclops,crabs,cray fish,
etc.
Includes the ticks, mites
,scorpion and spiders.
consists of mosquitoes,
fleas, bugs, lice ,flies,
etc.
Species

41. Identification
 Knowing the insect order gives you valuable information about many insects in the same order. This
information includes:
• The type of mouthparts (informing how the insect feeds and giving clues for its control)
• Life cycle (indicating best times for control)
• Type of habitation, including host(s) (where to find it)
Beyond the family category, however, identification is very difficult for all but the most common insects
without a magnifying instrument such as a microscope.
The following identification strategies are useful for gardeners:
• Experience—Periodically attend plant clinics and hands-on advanced training to gain valuable practice in
insect identification. Working with experienced master gardeners also helps you develop valuable insight
into solving plant problems when plant disease and other factors can make analysis difficult.
• Specimen approach—Use keys, photographs, drawings and descriptions, along with insect specimen data.
• Symptoms approach—Compare damage with the insect’s physical characteristics (Figure 8). For example,
because of their different mouthparts, a beetle can cause chewing damage, but an aphid cannot.
• Host approach—Check references that list hosts and potential insect damage. Like people, many insects
have preferences for their meals.
• Host location approach—Use this method to exclude certain insects. For example, large praying mantid
species are not expected to be found in Alaska unless released. Also, some insects prefer dry or wet
conditions.

42. Identification
 Knowing the insect order gives you valuable information about many insects in the same order. This
information includes:
• The type of mouthparts (informing how the insect feeds and giving clues for its control)
• Life cycle (indicating best times for control)
• Type of habitation, including host(s) (where to find it)
Beyond the family category, however, identification is very difficult for all but the most common insects
without a magnifying instrument such as a microscope.
The following identification strategies are useful for gardeners:
• Experience—Periodically attend plant clinics and hands-on advanced training to gain valuable practice in
insect identification. Working with experienced master gardeners also helps you develop valuable insight
into solving plant problems when plant disease and other factors can make analysis difficult.
• Specimen approach—Use keys, photographs, drawings and descriptions, along with insect specimen data.
• Symptoms approach—Compare damage with the insect’s physical characteristics (Figure 8). For example,
because of their different mouthparts, a beetle can cause chewing damage, but an aphid cannot.
• Host approach—Check references that list hosts and potential insect damage. Like people, many insects
have preferences for their meals.
• Host location approach—Use this method to exclude certain insects. For example, large praying mantid
species are not expected to be found in Alaska unless released. Also, some insects prefer dry or wet
conditions.

43. The medically important classes are the
following
•
Apterygota Pterygota
SiphonapteraFleas Anopluralice
Diptera Dictyoptera Hemiptera

44. 1. Class Insecta
This class is divided into four orders
(a) Order Diptera: this order consists of mosquitoes and
flies. They have one pair of wing and development is by
complete metamorphosis.
(b) Order Siphonaptera: consists of fleas. Arthropods in
this order are wingless but have strong leg to help them
jump. Their development is by complete metamorphosis.
(c) Order Anoplura: Is order consists of lice, which are
wingless and with short legs. Their development is by
incomplete metamorphosis.
(d) Order Hemiptera- This order consists of bugs. Bugs
have rudimentary wings and develop by incomplete
metamorphosis.

45. Class Insecta
Common names
Order
Flies, gnats, mosquitoes…
Diptera
sucking lice
Anoplura
Fleas
Siphonaptera
True bugs
Hemiptera
Chewing lice
Hymenoptera
Ants, bees, wasps
-Mallophaga
Butterflies, moths
Lepidoptera
Grasshoppers, Crickets
Orthroptera
Beetles, weevil’s
Coleoptera
Cockroaches
Dictyoptera
Termites
Isoptera

46. 1- Diptera
• Diptera (flies, mosquitoes, gnats, midges) :
• the order diptera are the two winged (di = two; ptera = wings).
- Undergo complete metamorphosis.
• Diptera are only able to take fluid food, which in the case of bloodsucking flies is obtained by injecting
the piercing mouthparts (proboscis) into living tissue. In other flies, food is liquidized externally by
puddling it with spongy mouth parts in digestive fluid regurgitated from the foregut (crop).
• Larvae may have mouth hooks or chewing mouthparts.
- Most are legless.
- Larvae of advanced forms (housefly and relatives) have no head capsule, possess mouth hooks, and
are called maggots.
- Lower forms, such as mosquito larvae and relatives, have a head capsule.
• Adults have only one pair of wings and are rather soft bodied and often hairy.
- They have either sponging (housefly) or piercing (mosquito) mouthparts.
- This order demonstrates a multitude of lifestyles.
• Houseflies are a nuisance as adults, but their larvae are major recycling organisms.
• Mosquitoes and others are vectors of human and animal diseases, although an important food source
for fish and wildlife populations.
• Many other members of this order are either parasitic or predaceous on other insects, which makes
them among the most important beneficial insect.

47. Differentiation between three kinds of mosquitoes
Aedes aegypti
Culex
Anopheles
Characteristics
Not in Yemen
In Yemen
In Yemen
Geographic distrib.
Black with silver
marks(tiger mosqu.)
Grey
Grey
Color
Parallel to surface.
Parallel to surface.
Makes angle 45
degrees with the
surface.
Resting position
-Non spotted.
-Non spotted.
-Spotted
Wing
Single, black &
spindle.
Eggs in group.
Single. Slipper like
with bilateral air
floats.
Egg
-C.piptens.
-A.arabinensis.
-A.sergenti.
-A.multicolor.
Common species
in Yemen.

48. Differentiation between three kinds
of mosquitoes
Aedes aegypti
Culex
Anopheles
Characteristics
Bite mainly in the
morning or evening
Most species bite
and rest outdoors.
Bite throughout the
night.
Indoors & outdoors.
During the day they
are inactive, resting
in dark
corners,treas.
Adult females bite
people, animals.
Bite active between
sunrise and sunset.
Indoors or outdoors.
Many species feed
on both or once of
humans & animals
blood.
Behavior
Dengue fever.
Rift valley fever.
Yellow fever.
Tularemia.
Avian malaria.
W.bancrofti.
-Human malaria.
-W.malayi.
Medical
importance

49. Order Siphonaptera
• Order Siphonaptera: ‘Siphon’ means tube, ‘a’ means
without, and ‘ptera’ means wing.
• These are the fleas. Fleas are wingless.
• They are all blood-sucking, temporary ectoparasites of
warm-blooded animals, mainly mammals, but a few
will feed on birds.
• Only a small proportion will attack humans.
• Fleas, like bedbugs, are comparatively host-specific,
but will often feed readily on other animals if their
preferred host is not available.

50. Order Siphonaptera
• Fleas are minute to small (from 0.8 mm to 5 mm) and have the following
characteristics: compound eyes are absent or each is represented by an single
ommatidium. Most fleas have a pair of small simple eyes (ocelli), although some
are blind, usually those which live on hosts with underground burrows.
• Antennae are short and can be folded into grooves in the head, mouth parts are
piercing-sucking, coxae are long and tarsi are five-segmented, cerci are small and
one segmented, and wings are absent.
• Fleas are flattened from side to side (laterally, as opposed to dorsoventrally in
most insects); this is a useful adaptation to enable them to move easily through
the hairs or feathers of their host.
• Their length ranges between 1-6 mm; they are oval in shape and light to dark
brown in color. The small head has a proboscis that projects down wards and small
antennae recessed into grooves.
• Fleas have powerful legs adapted for jumping and can leap 10-15 cm.
• The abdomen is the bulkiest part of the body and is conspicuously segmented.
• The ending is rounded in the female, whereas in male the genitalia are apparent.
Metamorphosis is complete. Eggs are oviposited on the host or more often in the
host’s nest; in the former case, eggs fall off prior to hatching. The legless larva
feeds upon such organic matter as may be available including fecal material from
adult fleas that contains blood residues

51. Order Siphonaptera
• They are vectors of disease. They are associated with
• mammals including man. All mammals have fleas of
their own
• (dogs, cats, etc). Diseases from these animals could be
• transmitted to one another and to human beings. The
bubonic
• plague is an epidemic between rats, flea and man.
• • Fleas are also causes for chigger on man and
• other animals.
• • Fleas are annoying and irritating.

52. Adult Flea

53. -Hemiptera
• Hemiptera (stinkbugs, plant bugs, flower bugs,
shore bugs)
• Metamorphosis is simple in this order.
• Nymphs usually resemble adults.
• Adults have piercing-sucking mouthparts and two
pairs of wings; the first pair is membranous and
thickened on the basal half, and the second pair is
membranous throughout.
• Adults and nymphs are both damaging in pest
species. Some species, however, are predators of
harmful insect pests and considered beneficials.