College of Agricultyre,Rewa,(M.P.)

Class- B.Sc.(Hons.) 1st year, Semester-2ndCourse title – Fundamental of EntomologyLecture note by Alam M A April 2, 2020--------------------------------------------------------------------------------------------------------------------

CONTENTS ( 05 Lectures)1 LEC.6. Body segmentation: Structure of head & its types

2 LEC7. Body segmentation: Structure of thorax and abdomen

3 LEC 8. Structure and modifications of insect antennae4 LEC 9. Structure, function and modifications of insect mouth parts: biting andchewing andpiercing and sucking types ( bug type)5 LEC 10. Structure and modifications of insect legs---------------------------------------------------------------------------------------------------------------------------------

Lecture 6&7

LEC.6. Body segmentation: Structure of head & its types

LEC7. Body segmentation: Structure of thorax and abdomen

Lec 6 Structure of head & its types

Insect body is divided into three separate regions i.e. head, thorax and abdomenand these region are called tagmata and grouping of body segments into distinctregions is acknowledged as tagmosis .

( source- internet fig.)

I. HEAD ;It is first and anterior part of the body which shows greatvariation in shpe and size in insects of different orders . it is formed bythe fusion of six segments namely pre-antennary,antennary, intercalary,mandibular, maxillary and labial segments. Head is attached orarticulated to the thorax through neck or Cervix. Head capsule is asclerotized structure and formed by the fusion of several hard plates(sclerites) and weak lining called suture.

( source- taken from internet)

posterior view of insect head capsule

( source-taken from internet)

Sclerites of Head

i. Vertex: it is the top sclerite of the head capsule and situated betweencompound eyes.

ii. Frons: It is the facial area below the vertex and above the clypeus.

iii. Clypeus: it is the scleritesituated below the frons and the labrum is attachedto it.

iv. Gena: it is the Lateral cranial area located below the compound eyes.

v. Occiput : the posterior part of the Cranial area is the occiput

vi Post occipital ; it is inverted “u”shapedsclerite situated posterior to occiput .

Sutures of Head:

i. Epicranial suture: it is Inverted `Y' shaped suture located medially on the top ofhead . The stem of the suture is known as a median suture /coronal suture whiletwo branches are called lateral suture /frontal suture. It is the place throughwhich molting take place.

posterior view of insect head capsule

( source-taken from internet)

Sclerites of Head

i. Vertex: it is the top sclerite of the head capsule and situated betweencompound eyes.

ii. Frons: It is the facial area below the vertex and above the clypeus.

iii. Clypeus: it is the scleritesituated below the frons and the labrum is attachedto it.

iv. Gena: it is the Lateral cranial area located below the compound eyes.

v. Occiput : the posterior part of the Cranial area is the occiput

vi Post occipital ; it is inverted “u”shapedsclerite situated posterior to occiput .

Sutures of Head:

i. Epicranial suture: it is Inverted `Y' shaped suture located medially on the top ofhead . The stem of the suture is known as a median suture /coronal suture whiletwo branches are called lateral suture /frontal suture. It is the place throughwhich molting take place.

posterior view of insect head capsule

( source-taken from internet)

Sclerites of Head

i. Vertex: it is the top sclerite of the head capsule and situated betweencompound eyes.

ii. Frons: It is the facial area below the vertex and above the clypeus.

iii. Clypeus: it is the scleritesituated below the frons and the labrum is attachedto it.

iv. Gena: it is the Lateral cranial area located below the compound eyes.

v. Occiput : the posterior part of the Cranial area is the occiput

vi Post occipital ; it is inverted “u”shapedsclerite situated posterior to occiput .

Sutures of Head:

i. Epicranial suture: it is Inverted `Y' shaped suture located medially on the top ofhead . The stem of the suture is known as a median suture /coronal suture whiletwo branches are called lateral suture /frontal suture. It is the place throughwhich molting take place.

ii. Epistomal suture: (Fronto clypeal suture) found between frons and clypeus.

iii. Clypeolabral suture: Found between clypeus and labrum.

iv. Post occipital suture: Groove adjoining to occipital foramen. Line indicating thefusion of maxillary and labial segment.

Posterior opening of the cranium through which aorta, foregut,ventral nerve cord and neck muscles passes is known as Occipital foramen.Endoskeleton of insect cuticle provides space for attachment of muscles ofantenna and mouthparts, called as Tentorium. The appendages like

a pair of compound eyes, 0-3 ocelli, a pair of antenna and mouth parts are calledas Cephalic appendages.

Functions of Head

i. Food ingestion ii. Sensory awareness iii. Coordination of bodilyactivities

TYPES OF INSECT HEADS

Based on the inclination of long axis of the head and orientation of mouth partsthere are three types of insect heads.

1) HYPOGNATHOUS (Hypo – below; gnathous – jaw)

This type is also called orthopteroid type. The long axis of the head makes a rightangles to the long axis of the body. Mouth parts are ventrally placed and projectdownwards.eg .grass hopper

grasshopper

2) PROGNATHOUS (Pro- infront ;gnathous – jaw)

This type is also called coleopteroid type. The long axis of the head is horizontal. Itis in line with the long axis of the body. Mouth parts are directed foreward. Eg:groung beetles.

3) OPISTHOGNATHOUS (Opistho – behind ;gnathous – jaw)

This type is also called hemipteroid type or opisthorhychous. Head is deflexed.Mouth parts aredirected backwards and held in between the fore legs. Eg:Stinkbug

( source- internet)

A - Prognathus type insects head B – Opisthognathus type head

LEC 7 Structure of thorax and abdomen of Insects:

II. THORAX ;It is second and middle part of the body which is divided intoprothorax, mesothorax and metathorax. Meso and metathorax are wing arewing bearing segments called as Pterothorax. Each thoracic segment is made upof three hard plates namely Tergum or Nota (dorsal body plate)Sternum ( ventralbody plate) and pluran ( lateral plate).

( source- fig. taken from internet)

Generalized structure of insect thorax

Thoracic nota: Thoracic notum are called as pronotum, mesonotum andmetanotum as per their location in the region.

Pronotum: this sclerite is undivided and Saddle shaped in grass hopper, Shield likein cockroach.

Pterothoracic notum: Have 3 transverse sutures (Antecostal, Pre scutal and

Scuto-scutellar) and 5 tergites(Acrotergite, Prescutum, Scutum, Scutellum andPost-scutellum)

Thoracic sterna: Vental body plate of each thoracic segments are called asprosternum, mesosternum and metasternum. Thoracic sterna is made up of asegmental plate called Eusternun and a intersternite called Spinasternum.Eusternum is made up of three scleritesviz.,presternum, basisternum andsternellum.

( source-taken from internet)

Thoracic pleura:it is the Lateral body wall of thoracic segment between notumand sternum. Seleritesof pleuron is called as pleurites. Pleural plate is dividedinto anteriorepisternum and posterior epimeron by Pleural suture.Pterothoracicpleuron provides space for articulation of wing and leg. Thoracicappendages are three pairs of legs and two pairs of wings. Two pairs of spiraclesare also present in the mesopleuron and metapleuron.

Functions of thorax: Mainly concerned with locomotion.

III. ABDOMEN: It is third and posterior region of the body . This is made up of 9-11segments (Uromeres) and is highly flexible region . abdominal segments aretelescopic in nature and are interconnected by a membrane called conjunctiva.Each abdominal segment is made up of only two sclerite namely dorsal body plate(tergum) and ventral body plate (sternum).the plura in the abdomen is found inthe form of membrain, Eight pairs of spiraclesare present in the first eight abdominal segments besides a pair of tympanum inthe first abdominal segment. Eight and ninth abdominal segments bear thefemale genital structure in female insects whilein male ninth segment bear malegenital structure. Abdominal appendages are genital organs and cerci.

Function: Concerned with reproduction and metabolism.

( internet)

LECTURE 8,9&10:

LEC 8. Structure and modifications of insect antennaeLEC 9. Structure, function and modifications of insect mouth parts: biting andchewing andpiercing and sucking types ( bug type)LEC 10. Structure and modifications of insect legs---------------------------------------------------------------------------------------------------------

LEC 8.Structure and modifications of insect antennaeSTRUCTURE OF INSECT ANTENNAE

Antennae is exclusively a sensory organ perceive the information like motion .orientation, odour, sound, humidity, and a variety of chemical signals. Greatvariation is seen among insects, but all of them have three segments: segments1 and 2 are termed as scape and pedicel, respectively. The third antennalsegments a multisegmented part is called the flagellum and each segments offlagellum are called flagellomere. A great variation is seen in this part amonginsects,

Scape – it is a basal segment of antenna which rest in a depression in thehead capsule called antennal socket which bear a pointed structure calledantennifer on which scape is placed. the scape is provided with muscles which

help the antenna to move about. Surrounding to antennal socket there is a ring ofsclerite termed as antennal sclerite.

Pedicel- It is segment of antenna and located below the fkagellum. It bearjohnston organ which detects motion in the flagellum (third and typically finalantennal segment).

Flagellum - It is third part of antenna and a multi segmented structure.The flagellum of "true" insects do not have any intrinsic muscles betweenflagellomere (segments of flagellum) as in case of Symphyla, Collembola andDiplura. In many true insects, especially the more primitive groups such asThysanura and Blattodea, the flagellum partly or entirely consists of a flexiblyconnected string of small ring-shaped annuli.

MODIFICATIONS OF INSECT ANTENNAE

1. ARISTATE

Aristate antennae are pouch-like with a lateral bristle.it is an important sensorystructures used to detect air movement and odors.it bear sensilla in several pitswhich lie ventrally on the basal one-third of the third segment of the antenna. Theantenna is three-segmented with a branched arista projecting dorsally from thethird segment.).Examples: House flies (order Diptera).

help the antenna to move about. Surrounding to antennal socket there is a ring ofsclerite termed as antennal sclerite.

Pedicel- It is segment of antenna and located below the fkagellum. It bearjohnston organ which detects motion in the flagellum (third and typically finalantennal segment).

Flagellum - It is third part of antenna and a multi segmented structure.The flagellum of "true" insects do not have any intrinsic muscles betweenflagellomere (segments of flagellum) as in case of Symphyla, Collembola andDiplura. In many true insects, especially the more primitive groups such asThysanura and Blattodea, the flagellum partly or entirely consists of a flexiblyconnected string of small ring-shaped annuli.

MODIFICATIONS OF INSECT ANTENNAE

1. ARISTATE

Aristate antennae are pouch-like with a lateral bristle.it is an important sensorystructures used to detect air movement and odors.it bear sensilla in several pitswhich lie ventrally on the basal one-third of the third segment of the antenna. Theantenna is three-segmented with a branched arista projecting dorsally from thethird segment.).Examples: House flies (order Diptera).

help the antenna to move about. Surrounding to antennal socket there is a ring ofsclerite termed as antennal sclerite.

Pedicel- It is segment of antenna and located below the fkagellum. It bearjohnston organ which detects motion in the flagellum (third and typically finalantennal segment).

Flagellum - It is third part of antenna and a multi segmented structure.The flagellum of "true" insects do not have any intrinsic muscles betweenflagellomere (segments of flagellum) as in case of Symphyla, Collembola andDiplura. In many true insects, especially the more primitive groups such asThysanura and Blattodea, the flagellum partly or entirely consists of a flexiblyconnected string of small ring-shaped annuli.

MODIFICATIONS OF INSECT ANTENNAE

1. ARISTATE

Aristate antennae are pouch-like with a lateral bristle.it is an important sensorystructures used to detect air movement and odors.it bear sensilla in several pitswhich lie ventrally on the basal one-third of the third segment of the antenna. Theantenna is three-segmented with a branched arista projecting dorsally from thethird segment.).Examples: House flies (order Diptera).

2. CAPITATE

Capitate antennae are abruptly clubbed at the end. Examples: redflour beetle.

CLAVATE

Clavate antennae are gradually clubbed at the end. Examples: butterfly(orderLepidoptera).

4. FILIFORM

Filiform antennae have a thread-like shape. Examples: Ground and longhornedbeetles (orderColeoptera), cockroaches (order Blattaria).

5. GENICULATE

Geniculate antennae are hinged or bent like an elbow. Examples: Bees and ants(orderHymenoptera).

6. LAMELLATE

Lamellate or clubbed antennae end in nested plates. Examples: Scarab beetles(orderColeoptera).

7. MONILIFORM

Moniliform have a beadlike shape. Examples: Termites (order Isoptera).

8. PECTINATE

Pectinate antennae have a comb-like shape.Examples:fireflies(orderColeoptera).

9. PLUMOSE

Plumose antennae have a tuft of long hairs at each flagellomeres. Examples:mosquitoes (order Diptera).

10. SERRATE

Serrate antennae have a saw-toothed shape. Examples: Click beetles (orderColeoptera).

11. SETACEOUS

Setaceous antennae have a whip-like shape. Examples: cockroach.

Bipectinate antenna – Presence of comb like structure on both side of theflagellomeres. Example –silkworm moth (Lepidoptera order)

(All figures are from internet)

LEC 9. Structure, function and modifications of insect mouth parts:biting and chewing andpiercing and sucking types ( bug type)

MOUTH PARTS-

Mouthparts are the appendages of head and mainly concerned with foodingestion. It greatly vary in insects which depend upon their feeding habit Theyare mainly of two types viz., Mandibulate (feeding mainly on solid food) andhaustellate (feeding mainly on liquid foodeg..piercing-sucking, sponging, andsiphoning type mouth parts of insects).The main mouthparts are the labrum,mandibles, maxillae (pluralof maxilla) and labium.

The labrum is a simple fused sclerite, often called the upper lip, and moveslongitudinally. It is hinged to the clypeus.

The mandibles, or jaws, are highly sclerotized paired structures that

move at right angles to the body. They are used for biting, chewing and severingfood.

The maxillae are paired structures that can move at right angles to the body andpossess 5 segmented palps called maxillary palp.

The labium (often called the lower lip), is a fused structure that moves

longitudinally and possesses a pair of 3 segmented palps( labial palp).

MODIFICATIONS

Mouthparts among insects of different orders vary greatly .But ,here we are goingto discuss the mandibulate and haustellate (bug Type) mouth parts of insects.

MANDIBULATE MOUTH PART / BITING CHEWING TYPE MOUTH PART

Mandibulate (chewing) mouthparts are used for biting and grinding solid foods.Examples: Dragonflies and damselflies (order Odonata), termites (order Isoptera),adult lacewings (order Neuroptera), beetles (order Coleoptera), ants (orderHymenoptera), cockroaches (order Blattaria), grasshoppers, crickets and katydids(order Orthoptera), caterpillars (order Lepidoptera).

Biting and chewing type: It is the primitive type of mouth part and consists offollowing parts.

i. Labrum : (Upper lip) It is flap like, bilobed structure and attached to the clypeusby an articular membrane. It is the upper lip and covers the mouth cavity fromthe above. It helps to. It holds the food in positionand push it into the mouth . TheInner surface of the labrum is referred to as epipharynx. It is amembranousstructure and continuous with the dorsal wall of pharnyx. It is anorgan of taste.

ii. Mandibles: it is a paired structures. and articulate with the cranium at twopoints. They are heavily sclerotised.and bear tooth on their inner border. Theteeth have distal incisorfor cutting food and proximal molar or grinding teeth.

iii. Maxillae: it is also a paired and more complicated structure. They are calledsecondary jaws or accessory jaws.it cosist of cardo an scleritewhich joins themaxilla to head. The second sclerite is called stipes which bear a lateral scleritecalled palpifer towhich a five segmented maxillary palp is attached . The distalend of the stipes, bear two lobes. The outer lobe is called galea and inner lobe islacinia which is toothed.

Maxille direct the food into the mouth byholding the food in place whenmandibles are in action and helps mastication of food. They also perceive thesens of touch, smell and taste are abundantly found in palpi.

iv. Hypopharynx : It is a tongue like organs located centrally in the preoral cavity.Salivary gland duct opens through it.

v. Labium /lower lip: It is a composite structure and bounds the mouth cavityfrom below . It forms the base of the preoral cavity. It consists of three scleritesviz., submentum (large basalsclerite), mentum (middle sclerite) and prementum(apical sclerite). On the lateral side of the prementum there are two small lateralsclerites called palpiger bearing three segmented labial palpi. Distally prementumbears two pairs of lobes. The outer lobes is called paraglossae and inner pair as,glossae. Both pairs when fused are called ligula.

Biting and chewing type mouthpart of cockroach

HAUSTELLATE MOUTH PARTS

Haustellate mouthparts are primarily used for sucking liquids and can be dividedinto two subgroups:1 those possess stylets and 2 those do not. Stylets areneedle-like structure used to penetrate plant and animal tissue. The modifiedmandibles, maxilla, and hypopharynx form the stylets and the feeding tube. Afterpiercing solid tissue, insects use the modified mouthparts to suck liquids from thehost. . One example of nonstylate mouthparts are the proboscis of butterfliesand moths (Lepidoptera).

1. Piercing-suckingmouthparts :Piercing-sucking mouthparts are used topenetrate solid tissue and suck up liquid food. Examples: Cicadas,

aphids,andother bugs (order Hemiptera), sucking lice (order Phthiraptera), stableflies and mosquitoes(order Diptera).

Piercing and sucking / hemipterous / bug type: e.g. Plant bugs. In this typemouth parts the Labium projects downwards to froman anterior beak/ rostrum.The beak is four segmented and grooved throughout its entire length. At the baseof the labium there is a triangular flap like structure called labrum. Labium act asas a protective covering for the four stylets (fascicle) found with in the groove.Both mandibles and maxillae are modified into long slender sclerotized hair likestructure called stylets. They are lying close together and suited for piercing andsucking. The tips of the stylets may have minute teeth for piercing the planttissue. The maxillarystylets are double grooved on their inner faces. When thesegroove are closely opposed they form two canals viz., food canal and salivarycanal through sap and saliva are conducted respectively. Saliva contains enzymesor toxins that can distort plant cell walland permit the stylets to penetrate deepdown to phloem for suking the sap. Both maxillary and labial palps are absent.

Piercing and sucking type mouthpart of plant bug

LEC 10. Structure and modifications of insectlegs

Structure ofinsect legs:legs are locomotory organ of insects . insects have

three pairs of legs called: fore-legs, middle-legs, and hind-legs which arise fromprothorax . mesothorax and meta thorax,respectively .all insect legs consist ofthe following segments,

1 Coxa, It is the proximal segment and functional base of the leg. It articulateswith the pleuron and associated sclerites of its thoracic segment, and in somespecies it articulates with the edge of the sternite as well.

.2 Trochanter . it is the second segment of leg and located between the coxa andthe femur.

3 Femur,.femur is the third (counting from the body) segment in the leg of aninsect. The femur is between the trochanter and the tibia. It is often the thickestor stoutest segment in the leg.

4 Tibia,Tibia. The tibia is the fourth segment in the leg of an insect and is locatedbetween the femur and the tarsus. In many species of insect the tibia is coveredwith spines and hairs. The pollen basket In bees is found on the tibia of the hindleg.

5 Tarsi.The tarsus( pleural-tarsi) is the terminal segment in the leg of the insect.The tarsi maycontains one to five segments called tarsomeres and usually endswith one or two claws forgrasping the substrate

6 Pretarsus – The structure found on the terminal of tarsus usually are claws withare without pad called pulvillus or a central pad (Aerolium-example grasshopper)or needle like empodium( example house fly) in different insects . These structureare called pretasus.

The Insect Legs shows legs modification for numerous purposes like running;jumping; digging; grasping; catching; walking and digging; and reduced leg used

for walking and digging; while male leg modified for grasping females duringmating.

Structure of a typical insect leg

Modification of insect legs : Following type legs are found in insects

1 Ambulatorial( Walking Type) eg. Ants.Femur and tibia and tarsi are

long structureIn this case. Some time trochanter is two segmented

2 Saltatorial( jumping) eg. Hind leg of grasshopper

Femur is a long and muscular structure and tibia too is elongated and cylindricalstructure, this leg is comparatively larger than other legs of the insect

3 Raptorial (Preying Type) :egforeleg of praying mantid

The size of the coxa to be large ,femur; broad and grooved and armedwith spines and tibia is cylindrical and spined which could be fit into thegroove of femur resulting the firm grasping on prey

4 Fossorial (digging type).eg. foreleg of mole cricket

These legs are Powerful, spadelike forelegs adapted for digging andrapid burrowing. Femur and tibia broad structure bearing nail like 5tarsi.

5 Natatorial ( swimming type)eg. giant water bug & water beetle

These legs are charachterized by presence of elongated setae on tarsi

6 Cursorial ( running type) eg. cockroach

Femur .tibia and tarsi are elongated structure in this case.

7 Scansorial –( Clinging typ) eg head louce

Tarsus is a single segmented and form a hook like device which impartthe clinging support to insect,

8 Suctorial - clinging by suctionegDyticus beetle (male)

In this case first tarsus segment become a large dish like structurebearing two cups like suction pad which help the insect in adhesion onthe surface or holdIng the female insect during mating .

9 Sticking type- ---- eg house fly

The terminal tarsi bear two claws and centrally a needle like structurecalled empodium which help the insect to walk on smooth surface.

10 ForagialType ( pollen collecting Type ) eg, hind leg of honey bee

There is a pollen comb on inner surface of Ist segment of hind tarsus toremove pollen from body,

A pollen basket on outer surface of hind tibia

Spur on the apex of middle tibia to scrape pollen from the baskets

Antennal comb on the front legs to remove pollen from antennia

empodium

The terminal tarsi bear two claws and centrally a needle like structurecalled empodium which help the insect to walk on smooth surface.

10 ForagialType ( pollen collecting Type ) eg, hind leg of honey bee

There is a pollen comb on inner surface of Ist segment of hind tarsus toremove pollen from body,

A pollen basket on outer surface of hind tibia

Spur on the apex of middle tibia to scrape pollen from the baskets

Antennal comb on the front legs to remove pollen from antennia

empodium

The terminal tarsi bear two claws and centrally a needle like structurecalled empodium which help the insect to walk on smooth surface.

10 ForagialType ( pollen collecting Type ) eg, hind leg of honey bee

There is a pollen comb on inner surface of Ist segment of hind tarsus toremove pollen from body,

A pollen basket on outer surface of hind tibia

Spur on the apex of middle tibia to scrape pollen from the baskets

Antennal comb on the front legs to remove pollen from antennia

empodium