prof. dr. badr el-sabah entomology lecture 1

Lecture 1

Introduction To Phylum Arthropoda

Class : Insecta

Prof.Dr. Badr El-Sabah / Lecture 11

Introduction To Phylum Arthropoda• The name Arthropoda would mean animals with jointed legs. (arthro:

jointed; poda: legs).

• The animals of this phylum have occupied almost all possible niches in this planet, be it land or water or soil; and there are parasites too.

• In terms of numbers also they are the largest group – there are about 900, 000 species.

• Their success could be attributed to a variety of factors:– Widespread distribution – Variety of habitats occupied– Varied food habits– Adaptations to overcome the harmful effects of the environment –

particularly the development of an impermeable exoskeleton –the cuticle.– Ability to adapt themselves to changing environment

Prof.Dr. Badr El-Sabah / Lecture 1 2

General Characters of Phylum Arthropoda

• The body is bilaterally symmetrical, triploblastic and metamericallysegmented.

• Jointed appendages which lie as one pair to a somite, and with varied functions as jaws, gills, legs, etc.

• The exoskeleton is composed of dead chitinous cuticle that is shed at intervals, called ecdysis or molting, for growth and development.

• The body is divisible into head, thorax and abdomen. Head and thorax are often fused to form a cephalothorax.

• True coelom is reduced and is largely replaced by a blood-filled haemocoel.

• The muscles are mostly striated, usually capable of rapid contraction.


4Prof.Dr. Badr El-Sabah / Lecture 1

General characters of Class Insecta

1) The head contains– a pair of compound eyes,

three frontal simple eyescalled ocelli

– a pair of antennae– a terminal mouth– Mouth parts modified for

different feeding habits.

– The 4 main mouthpartsare the labrum,mandibles, maxillae(plural maxilla) andlabium.

2) The thorax• The insect thorax is

divided into three parts:I. prothorax (pro=first)II. mesothorax

(meso=middle)III. metathorax (meta=last).

• Each of the threethoracic segmentscontains one pair oflegs.

• Wings are found onlyon the meso- andmetathoracic segments.

3) The abdomen• The abdomen contains

the reproductive organsand the majority of theorgan systems

• Spiracles usually can befound in the conjunctivetissue between the tergaand sterna of abdominalsegments 1-8

• Reproductive structuresare located on the 9thsegment in males and onthe 8th and 9th

abdominal segments infemales .

• The segmented body is divided into three typical regions, namely a head(6 fused segments), a

thorax (3 segments) and an abdomen(11 segments)


http://www.entomology.umn.edu/cues/4015/morpology/





• Each segment consists of hardened plates,or sclerites. The dorsal plate is calledtergum and the ventral plate is calledsternum. lateral plates are called pleura(singular pleuron)

• The respiration is by trachea. Spiracles arepresent laterally.

• Excretion by Malpighian tubules.

• Unisexual and fertilization is internal.

• Development usually takes place withmetamorphosis.

General characters of Class Insecta(cont)


Complete Metamorphosis

(Holometabolous)

• Each of the developmental stages is

structurally and functionally very different

• The egg develops into an immature larva;

eats voraciously

• Followed by a transitional stage - pupa,

contained within cocoon

Metamorphosis occurs within the pupal

exoskeleton, yielding a sexually mature

adult

(egg --> larva --> pupa --> adult).

Early developmental stages are very

similar to the adults.

only the wings and the reproductive

structures gradually develop

• The immature stages are called

nymphs

(egg --> nymph --> adult)

Incomplete Metamorphosis

(Hemimetabolous)


Basic Definition:

1. external skeleton2. 3 distinct body regions3. 3 pairs legs on 3 thoracic segments4. 1 pair sensory antennae5. (usually in adult) 1 pair compound eyes6. (usually in adult) 1 or 2 pair of wings

What Is an Insect?


Other Defining Features:

7. External mouthparts (mandible, maxillae, labium)8. Eyes primitively with 2 pigment cells9. Thoracic legs with maximum of 6 segments10. Abdomen primitively with 11 segments11. Antennae with 2 musculated segments (scape &flagellum)12. Ocelli (in addition to compound eyes)13. Gonopore on segment 8 or 9, cerci on seg. 1114. Well developed Malpighian tubules15. Embryonic development by superficial cleavage16. Epimorphic (cf. Anamorphic), number ofsegments fixed

(What Is an Insect?)


THE IMPORTANCE OF ARTHROPODS

>>Natural World<<Effects are “Neutral”

CONTRIBUTIONS OF INSECTS TO:

• Community structure - nutrient cycling, vegetation structure

(phytophagy, pollination, seed dispersal)

• Population dynamics - predators & parasites, disease

transmission

• Food webs - food for other animals.


POLLINATION – FLOWERE POLLINATORS


Negative Influences

Agriculture: competition for food & fiber apple maggot, bark beetlesDomestic: damage to property & goods termites, silverfish, dermestidsMedicine: parasites & disease malaria (via mosquitoes), bot flies, screw worm fly

THE IMPORTANCE OF ARTHROPODS

>>Anthropocentric World<<

• Defined best by Human Culture & $Economy$• Negative & Positive Effects


Positive Influences

Agriculture: biocontrol, pollination lady beetles, honey bees, solitary bees

Medicine: antibiotics, chronic disease treatment, maggot debridement,honey bee venom, maggots

Commerce: products, cochineal, silk, wax, honey scale insects, silkmoth, honey bees

Science: ideal subjects for experimentation, genetics (Drosophila)ecology, physiology vinegar “fruit” flies, tobacco hornworm,honey bees

Aesthetics: art & inspiration butterflies, beetles, fireflies

Food: nutrition, environmental, economic soundness 500 species, 17families, especially grubs & caterpillars


Beekeeping

Silk Industry

BiologicalControl


Insect Evolutionary/Ecological Success:

SPECIES RICHNESS & NUMBERSWhy are insects so diverse?

Possible reasons:

Relative size (more niches) Short generation time (rapid evolution) Holometabolism (specialization) Powered flight Sensory & motor neuron sophistication Preadapted for coevolution with other organisms Geologic age Sexual selection Phytophagy


External Morphology

Ofinsects


Tagmosis in general body regions. Insect fundamentalsegment number: 6, 3, 11.


Fig. 2.7, Gullen & Cranston 2000

a) insect larvab) “secondary’ segmentationc) “derived” secondary seg.d) advanced winged insect

Increasing sophistication of body

segmentation


1

2

6

5

4

Insect head segmentation.

post antennal segment (compound)3


Generalized insect MOUTHPARTS

!20Prof.Dr. Badr El-Sabah / Lecture 1

Insect Body-parts

A brief guide to the

main external

features of insects

and the terminology

used to describe the

various body-parts.


The insect body is divided into three main parts - head,thorax and abdomen - as shown above.Head. The head bears the mouthparts, the eyes and apair of antennae (singular: antenna). Most adultinsects and the immature stages (nymphs) ofExopterygota have a pair of large, multi-facetedcompound eyes (labelled 'eye' in the diagram above).Many of these insects also have two or more small,single-faceted eyes, called simple eyes or ocelli(singular: ocellus), usually placed on the top or front ofthe head between the compound eyes


In some insects, particularly those

belonging to the Apterygota, and in the

immature stages (larvae) of all

Endopterygota, compound eyes are

lacking and only ocelli are present, with

one or more of these simple eyes on

each side of the head. In a few adult

insects and among many larval forms,eyes are completely absent.


Thorax. The thorax consists of three segments - the

prothorax (front), the mesothorax (middle) and the

metathorax (back). Each of these segments bears a

pair of jointed legs. Each leg consists of four main

parts - the coxa, the femur, the tibia and the tarsus

(plural: tarsi) - with a small, often inconspicuous

segment between the coxa and femur, called the

trochanter. The tarsus usually consists of several

small joints, the last of which generally carries a pair

of terminal claws. The last tarsal segment may be

extended between the claws to form a pad-like

organ - the arolium (as in (1) below).


Some Diptera (true flies) have two additional pads - the

pulvilli (singular: pulvillus) - lying below the claws on

either side of the arolium (as in (2) below), although in

most flies, including the common housefly and its

relatives, the arolium is replaced by a stout central

bristle - the empodium (as in (3) below). In many

insects, the other tarsal segments also have ventral

pulvillus-like organs, called plantulae. These various

structures - the arolium, pulvilli and plantulae - produce

a sticky secretion and act like 'suction-pads', enabling

the insect to climb smooth or steep surfaces. This is the

secret of the fly's ability to walk up-side-down on the

ceiling!


Terminal Segments of the Tarsus (see text above for

details)

(1) (2)(3)

(a = arolium, c = claw, e = empodium, p = pulvillus)

In winged insects, the meso- and metathoracic segments each bear a

pair of wings (the forewings and hindwings, respectively), although in

many insects one or both pairs of wings have been lost, or modified into

other structures, during the course of evolution. Special wing

modifications include the structures called halteres found in the Diptera

(true flies), and the structures called elytra (singular: elytron) found in

the Coleoptera (beetles) and Dermaptera (earwigs):


Halteres - small, club-shaped

organs of balance found in

Diptera (flies) on each side of

the thorax (metathorax) just

behind the forewings and

thought to be modified

vestigial hindwings.


Elytra (singular: elytron) - the

hard, leathery forewings of

Coleoptera (beetles) and

Dermaptera (earwigs), that serve

as protective coverings or 'wing-

cases' for the membranous

hindwings. The hindwings (if

present) are usually folded out of

sight under the elytra when at rest.

The diagram shows a green tiger

beetle (Cicindella campestris) with

the elytra open and hindwings

outstretched, as the beetle

appears when in flight.


Abdomen. The abdomen is made up of

several, more or less similar segments

and often bears a pair of jointed, terminal

appendages called the cerci (singular:

cercus). Typical cerci are illustrated in

(a) below, although in some insects they

consist of many more joints than in the

example shown.


Abdominal Appendages of Adult Insects

(a)

typical cerci

(b)

cerci and tail

filament

(c)

cerci modified

as

forceps e.g.

earwigs

(d)

paired

cornicles

e.g. some

aphids


In the immature stages (larvae) of some

Endopterygota, e.g., those of many

butterflies and moths (Lepidoptera),

scorpion flies (Mecoptera) and sawflies

(Hymenoptera), the abdomen carries

several pairs of appendages called false-

legs or prolegs. These are unjointed, fleshy

structures different from, and additional to,

the jointed legs of the thorax. Larvae with

prolegs are commonly called caterpillars.


Caterpillar of a Sawfly -

side-view showing: (a) the

jointed legs (i - iii) of the

thorax, and (b) the fleshy

prolegs (i - vii) of the

abdomen. There are always

three pairs of thoracic legs

(as characteristic of insects

generally), but the pairs of

abdominal prolegs may vary

in number depending on

species.


THANKS
