Insects play a crucial role in ecosystems, serving as pollinators, decomposers, and maintaining the balance of nature by controlling pest populations. The study of insects, known as entomology, involves understanding their physical characteristics, including segmentation, mouthparts, and antennae, which contribute to their diverse functionalities. Various classifications of insects exist, based on traits like mouthpart types, leg adaptations, and wing structures, highlighting their complexity and importance.

2.  Insects are important to everyone, they are found
almost any place and on almost everything. As you
become more familiar with
 insects, you will be fascinated with the wide variety of
forms and their ways of life. Many people have made
the collection and
 identification of insects a useful hobby, others have
made this science of insect study their life work.
 The study of insects is a science called entomology.
A person who studies insects is called an
entomologist.

3.  Insects have three pairs of legs and no internal
skeleton (bones). The external skeleton (exoskeleton)
is a waxy, durable, flexible
 substance called CHITIN. Because of the unusually
stable character of this exoskeleton, insects can be
kept for many years without
 preservation, and still retain a lifelike appearance after
death.

5. 1. The head
2. The thorax
3. The abdomen
 The head bears the eyes, the antennae and mouth
parts.
 The next division behind the head is the thorax;
attached to it are the wings and legs.
 The third part is the abdomen. Here we find the
spiracles or openings through which insects breathe.

6. Insects as pollinators. Insects pollinate many of our fruits, flowers, and vegetables. We
would not have much of the produce that we enjoy and rely on without the pollinating
services of insects.
Many insects are predatory or parasitic, either on plants or on other insects or animals,
including people. Such insects are important in nature to help keep pest populations (insects
or weeds) at a tolerable level. We call this the balance of nature. Predatory and parasitic
insects are very valuable when they attack other animals or plants that we consider to be
pests.
Insects are very important as primary or secondary decomposers. Without insects to help
break down and dispose of wastes, dead animals and plants would accumulate in our
environment and pollution happen.
They are the sole food source for many amphibians, reptiles, birds, and mammals. hey are a
rich source of protein, vitamins, and minerals.

8. Phyllum: ARTHROPODA
There are 5 common classes:
1. Class: Crustacea eg. Crayfish, sowbugs, shrimps
2. Class: Diplopoda eg. Millipede
3. Class: Chilopoda eg. Centipede
4. Class: Arachnida eg. Mites, ticks, spiders
5. Class: INSECTA

9. Characteristics of the Class: INSECTA
1. The body is divided into 3 distinct regions:
a) The head –
b) The thorax – with 3 pairs of legs; 1 or 2 pairs of
wings
c) The abdomen – with spiracles
2. Segmented body
3. Chitinous Exoskeleton – “armour” for protection,
moisture retention, muscle attachment
4. Have 3 (three) pairs of legs

11. A. Classification of insect based on orientation of the
head in relation with the position of the mouthparts:
1. Hypognathus – mouthparts hung vertically from the
head capsule (mouthparts pointed downwards)
2. Prognathus – mouthparts directed anteriorly (pointed
forward)
3. Opisthognathus – mouthparts directed
ventroposteriorly (downward and backwards)

13. B. Classification based on types of mouthparts:
The mouthparts can be broadly divided into 2 groups:
1. Chewing mouthparts (mandibulate mouthparts) –
generally adapted to chewing activities with the
mandibles act as cutting and grinding structures eg.
Predaceous beetles
2. Sucking mouthparts (haustellate mouthparts):
2 types:
a. Stylate haustellate
b. Non-stylate haustellate

14. Haustellate mouthparts:
• generally adapted for sucking activities of various
sorts
•Many are characterized by the presence of the
stylets which are needle-like or with saw-like
modifications
•Stylets may be formed from a combination of one or
more of the mouthparts and the hypopharynx
•Not all haustellate mouthparts have piercing stylets
eg. Butterflies, moths, muscoid flies

17. Typical mouthparts consist of:
1. The anterior upper lip called the labrum
2. the hypopharynx (tongue)
3. a pair of mandibles (primary jaws)
4. A pair of maxillae ( secondary jaws)
5. A posterior lower lip called the labium

18. C. Classification by types of antenna
•Paired antennae are located between and in front of
the eyes
•Function of antennae is sensory;
•They vary in form and size and have considerable
value in identification in certain families and
•some to differentiate the sexes e.g. mosquitoes
•Usually described as being of a particular type
(capitate) or combination of types (capitate-lamellate)
•In some insects they function as grasping structure to
grab the prey

20. D. Classification by types of legs
• Typically for movement – walking or running
• Most have been extensively modified
a. Cursorial - adapted for running and walking
b. Fossorial - adapted for digging, heavily
sclerotized forelegs eg. Mole cricket, nymphs of
cicadas
c. Raptorial - modified for grabbing and holding
prey; forelegs for grasping eg. Praying mantis
d. Saltorial - adapted for jumping; Femora of hind
legs enlarged to accommodate muscle for jumping
eg. Grasshoppers
e. Natatorial - adapted for swimming; presence of
“swimming hairs”.

23. E. Classification by type of wings
•Insects may bear a single pair of wings or two pairs or
non at all
•Many wingless insects are grouped with the winged
insects on the basis of developmental and morphological
similarities
•Wing sizes vary from very small (wasps, flies) to very
large (large butterflies and moths)
•Venation – because of variation in wing venations, they
are used as a source of taxonomic characters

24. Wing Venation, Function & Texture
 Because of variation, wing venation has been used as
a taxonomic character
 Venation ranges from extensively reduced and
simplified (wasps) to highly complex (dragonflies)
 most obvious function is for flight
 In some insects (beetles) the forewings modified into
hard elytra (elytron) protecting the membranous hind
wings
 In some the forewings are partly hardened –
hemelytra or “half elytra”
 In Orthoptera, tegmen is present to protect the hind
wings
 In true flies, the hindwings are highly modified into
Halteres (balancing organ) for flight stability

26. Species are not created as “pests.
Animals or plants that are in places or at times where humans do not want them to
be are considered pests.
It is necessary to understand the role of invertebrate species in ecosystems.
In most cases, small numbers of pest insect species can be tolerated without
significant crop damage. However, when insect populations reach a threshold level,
cumulative damage from many thousands of insects becomes unacceptable.
Besides, even the most insignificant pest can become a major problem if present in
high enough numbers.