The document discusses the class Insecta, describing their key characteristics including three body parts (head, thorax, abdomen), compound eyes, trachea respiration, and undergoing metamorphosis. It outlines the 31 orders of insects, divided into 4 apterygota and 27 pterygota orders. The lecture emphasizes both the beneficial and detrimental effects of insects, highlighting their importance as pollinators, food sources, and use in research, as well as some insects being parasites, disease vectors, or destroying crops and structures.

1. Lecture no. 2
Importance of class insecta
R K PANSE
Assistant Professor
Entomology

2. Class insecta
Insects are invertebrates grouped in the phylum Arthropoda
(Arthro-joint, poda-foot) and class Insecta. Characters of the
class insect are
 Insects like other mandibulates have one pair of pre-oral
antenniform appendages
 The insect body is usually divided into three parts – head,
thorax and abdomen
 The insect head consist of six segments.
 Compound eyes are present
 The thorax consists of three segments and three pairs of
walking legs ventrally and two pairs of wings dorsally
 The abdomen consists of eleven segments usually and bears
no ambulatory appendages
 Insects respire by means of trachea which open via
segmentally- arranged spiracles.
 Excretion in insects is by means of Malpighian tubules
 Insects undergo metamorphosis.

3. •The class Insecta is divided in to 31 orders (4 in Apterygota and 27 in
Pterygota).
Apterygota
1. Thysanura - Silverfish (Thysan-fringed, Ura-tail)
2. Collembola- Springtail or snowflea (coll-glue; embol-peg)
3. Protura - Proturans or Telsontail (Pro-first, Ura-tail)
4. Diplura - Diplurans or Japygids (Di-two; Ura-tail)
PTERYGOTA orders
Exopterygota division
01. Ephemeroptera - Mayflies
02. Odonata-Dragonfly, Damselfly

4. 03. Plecoptera - Stonefly
04. Grelloblatodia - Rock crawlers
05. Orthoptera-Grasshopper, locust, cricket, mole cricket
06. Mantophasmatodea- leaf stick insect
07. Phasmida-stick insect, leaf insect
08. Dermaptera-Earwigs
09. Embioptera-Webspinners/Embids
10. Dictyoptera-cockroach, preying mantis
11. Isoptera - Termites
12. Zoraptera - Zorapterans
13. Psocoptera - Book lice
14. Mallophaga - Bird lice
15. Siphonculata - Head and body louse
16. Hemiptera – Bugs
17. Thysanoptera - Thrips

5. Endopterygota division
01. Neuroptera- Antilions, aphidlion, owl flies, mantispid flies.
02. Mecoptera - Scorpionflies.
03. Lepidoptera - Butterflies and moths.
04. Trichoptera - Caddisfly.
05. Diptera - True fly.
06. Siphonaptera - Fleas.
07. Hymenoptera - Bees, wasps, ants.
08. Coleoptera - Beetles and weevils.
09. Strepsiptera - Stylopids.
10. Raphidioptera – snakefly

6. Importance of class insecta
Beneficial Effects of Insects
 Insects pollinate flowers hence, fruit formation depends on them
 Insects form a source of food for man e.g. honey, termites,
caterpillar
 Useful materials such as silk, bee wax, etc are obtained from
insects
 Insects are important in food chains, e.g. Aquatic insects form
food for the fishes
 Insects are important as scavengers – (decomposition involving
cycling of materials)
 Insects are important tools, e.g. Drosophila is used for research
in genetics, physiology etc.
 Some insects are used to control others that are pests (Biological
Control)
 Insects have aesthetic value (e.g. Butterflies are collected for
their beauty).

7. Detrimental Effects of Insects
 Some insects are parasites of animals and plants e.g. Lice, and
stem- boring caterpillars.
 Some insects e.g. mosquitoes and tsetse flies are vectors of
parasitic diseases.
 Some insects e.g. bean weevils destroy crops and stored food.
 Some insects e.g. termites destroy wooden structures.
 Some insects e.g. house fly and mosquito are often nuisance to
man. The beneficial effects of insects, however, far outweigh
their adverse effects.