Entomology

Branch of zoology that focuses on study of insects i.e. everything about insects. In the strict sense, entomology is the study of insects, but entomologists often study other arthropods such as spiders, scorpions, mites, millipedes, centipedes

Insects

Insects have 3 body regions i.e. head, thorax and abdomen
Head contains antennae, mouth parts, compound eyes, ocelli (simple eyes)
Thorax contains three pair of legs and two pairs of wings
Abdomen contains spiracles and reproductive organs
Their body size may range from 1mm to 30mm (11.8 inches)

Classification of insects

Kingdom—Animalia
- Phylum—Arthropoda
- Class—Insecta
- Order— Diptera (only the true flies)
- Family —Syrphidae (only the hoverflies)
- Genus—Episyrphus (only s sub-set of the hoverflies)
- Species—balteatus

(Species): Group of individuals that actually or potentially interbreed in nature.

Interesting facts about insects

Insects are the most biodiverse group of organisms on earth in terms of abundance and number of species.
Approximately 1 million insect species have been described (comprising 80% of word’s species)
It is believed that 2 to 30 million species exist worldwide; 6,000-7,000 new species of insects are described annually

Insects are the most successful group of organisms on earth

Insects have lived on earth for at least 350 million years; 9 million years earlier than dinosaurs.
Insect live everywhere, every habitat from sands of hot deserts to cold Snowy Mountain streams; at least 40 species of insects live in Antarctica (-50°C) while hundreds of species live in deserts at 50°C.
Habitats of insects include: rain forests, fresh water, grasslands, agriculture, urban areas etc.
Fewer than 1% of all the insect species are serous pests; they may affect humans, their animals, crops, structure and can transmit diseases (pathogens) to plants (e.g. cotton leaf curl virus is spread by whitefly), humans (malaria by mosquitoes) and animals (dog tapworm by fleas).
Insects may also be beneficial e.g. pollinators, biological control, honey, wax, silk, shellac, medical therapy
A swarm of migratory locust may contain up to 10 billion individuals (1 billon=1000 million)
40,000 cicadas may feed on single large tree.
Single African ant colony may contain 20 million individuals
Brazilian Amazon ants alone may outweigh the total biomass of vertebrates by four to one.

Assignment: What are ecosystem services and which ecosystem services are performed by insects?

Characters of Phylum Arthropoda

It is largest phylum among invertebrates. (Arthro-Jointed, Poda-Legs) They have:

Segmented body
Sclerotised exoskeleton
Paired jointed appendages
Bilateral symmetry
Body cavity or haemocoel having haemolymph
Food track consisted of forgut, midgut and hindgut
Dorsal blood vessel
Ventral nervous system
Striate muscles

Classification of Arthropods

(1) Class Onychophora, (2) Class Chilopoda, (3) Class Diplopoda, (4) Class Symphyla, (5) Class Pauropoda, (6) Class Arachnida, (7) Class Crustacea, (8) Class Insects

Class Onychophora

Body is cylindrical
Two body regions i.e. head and trunk
Trunk bears 15 pair of stumpy legs
Head has two antennae and two simple eyes
Example: Peripatus

Class Chilopoda

Body is long and flattened
Two body regions i.e. head and trunk
Head has two antennae and two clusters of simple eyes
Trunk carries a pair of leg in each segment
First pair is modified into poison claws
Example: Centipedes

Class Diplopoda

Body is long and cylindrical
Two body regions i.e. head and trunk
Head has two antennae and two clusters of simple eyes
Trunk bears two pair of legs in each segment except first 4 segments
Example: Millipedes

Class Symphyla

Very small in size
Two body regions i.e. head and thorax
Head has two long antennae and no eyes
Trunk has 12 pair of legs
Example: Symphylans

Class Pauropoda

Very small arthropods
Two body regions i.e. head and trunk
Head with a pair of 3 branched antennae and no eyes
Trunk has 9 to 11 pair of legs
Example: Pauropods

Class Arachnida

Body is divided into Cephalothorax (head and thorax are fused) and abdomen
No antennae
No wings
4 pair of legs on cephalothorax
Example: spiders, scorpions, mites, ticks

Class Crustacea

Body is divided into cephalothorax and abdomen
Cephalothorax with two pair of antennae and 5 pair of walking legs
Most are aquatic and some terrestrial
Cray fish, crabs, prawns, lobsters

Class Insecta

Three body regions i.e. head, thorax and abdomen
1 pair of antennae, 1 pair of compound eyes
Three pair of legs, 2 pair of wings
Example: dragon fly, wasp, ants

Metamorphosis

The changes in form that occur as an insect approaches adulthood.

Types of metamorphosis

Ametabola:

No metamorphosis
Young ones are called nymphs
Young ones similar to adults with only few differences i.e. size and gonads
Primitively wingless (Apterygota)
Egg Nymph Adult
Example: Silver fish

Hemimetabola:

Hemi means half, simple or incomplete metamorphosis
Young ones are called nymph
Young ones are similar to adults with incomplete development of wings (wing pads present)
Wings develop externally (Exopterygota)
Egg Nymph Adult
Example: Red cotton bug

Holometabola:

Complete metamorphosis
Young ones are called larvae
Immature insects and adults are of different forms
Wings develop internally (Endopterygota)
Egg Larva Pupa Adult
Example: Butterfly

Types of Insect eggs

Spherical: Lemon butterfly, red cotton bug

Oval: Silverfish, mango mealybug

Conical: Beet army worm

Elongate: Housefly, Ack grasshopper

Stalked: Whitefly, green lacewing

Appendiculate: Water scorpion, stinkbug

Sculptured: Malarial mosquito, spotted bollworm

Elliptical: Earwigs, cotton cushion scale

Scale like: Maize borer, jelly moth

Types of insect eggs

Types of insect larvae

Campodeiform:

Elongate, flattened body
Long thoracic legs
Cerci on end of abdomen
Example: Rove beetle, diving beetle larvae

Carabiform:

Elongate, flattened body
Shorter thoracic legs
No cerci
Examples: Ground beetle, fire flies larvae

Eruciform:

Body cylindrical
Thoracic legs and abdominal legs (Pro legs)
Example: Butterflies and moths larvae

Scarabaeiform:

Body cylindrical, C-shaped
Thoracic legs well developed
Examples: Dung beetle, pulse beetle larvae

Elateriform:

Body thin, elongate and cylindrical
Short thoracic legs
Examples: darkling beetle larvae

Platyform:

Body very broad
Short or no legs
Example: Syrphid fly larvae

Vermiform:

Body cylindrical, elongate
Body narrowing from anterior
No legs
Example: Housefly larvae

Common names of Eruciform larvae

Caterpillar: Prolegs on 3^rd, 4^th, 5^th, 6^th and 10^th abdominal segments

Semilooper: Prolegs on 5^th, 6^th and 10^th abdominal segments

Looper: Prolegs present on 6^th and 10^th abdominal segments

Insect appendages

These are outgrowth of body wall which are moveable and connected with it by a membrane

Antennae

Pair of jointed sensory appendages