sclerites of thoraci segment in insect

in thorax of insect which sclerites is seeing

1. SCLERITES OF THORACIC SEGMENT
Assignment on
PREPARED BY:
Rudani Gaurang K.
M.Sc.(Agri.)Entomology
Semester: 1
st
C. P. College of Agriculture,
S. D. Agricultural University,
Sardarkrushinagar
SUBMITTED TO:
Dr. P. S. Patel
Associate Professor
Dept. of Agril. Ento
C. P. College of Agriculture,
S. D. Agricultural University,
Sardarkrushinagar

2. INTRODUCTION
Thoraxisthebodyregionsituatedbetweenheadandtheabdomen.
Theinsectthoraxisdividedintothreeparts:
a)Prothorax(pro=first)
b)Mesothorax(meso=middle)
c)Metathorax(meta=last)
Theinsectthoraxisabox-likestructureandiscomposedofanumberofscleriteswhichplay
animportantroleininsectlocomotion.
Eachsegmentconsistsofhardenedplates,orsclerites.
1.Dorsalsclerites-notum
2.Lateralsclerites-pleuron
3.Ventralsclerites-sternum
Eachofthethreethoracicsegmentscontainsonepairoflegsarisefrompleura.Wings
articulatedbetweennotalandpleuralregions.

3. Fig. Three regions of the insect body

4. Legs articulated on ventro lateral position
one pair on prothorax
one pair on mesothorax
one pair on metathorax
Wing articulated on dorso-lateral position
one pair on mesothorax
one pair on metathorax
Two slit like opening present on thorax known as spiracles
one pair between prothorax and mesothorax
one pair between mesothorax and metathoax

5. Prothoraxneverberaswingsanditmayvaryinsize.Sometime,the
dorsalregionsofprothoraxenlargedandfromshieldlikestructure
knownaspronotum.e.gorthoptera.Thepronotumisthedorsalsclerites
oftheprothorax,whichcanbehighlymodifiedinvariousorderssuchas
thehemiptera,blattadiaandcoleoptera.
Scleritesofthoracicsegment
Protergumisrefersasthetergumoftheprothorax,
Mesotergumisthetergumofmesothoraxand
metatergumisthetergumofmetathorax

6. THORACICSEGMENTATION
Inlarvalholometabolousinsectsthecuticleissoftandflexible,oronlypartially
sclerotized,andlongitudinalmusclesareattachedtotheintersegmentalfolds.
Thisrepresentsaprimitiveconditioncomparablewiththatoccurringintheannelids.
Whenthecuticleissclerotized,scleritesintheintersegmentalfoldswhichhave
longitudinalmusclesattachedtothemareusuallyfusedwiththesegmentalsclerites
behind.
Anteriorlyitincorporatestheintersegmentalregion,theoriginalfoldbeingmarkedby
theantecostalsulcuswherethecuticleisinflected.

8. Thenarrowrim-acrotergitewhichneveroccursatthefrontofthe
prothoraxbecauseanteriorpartofthissegmentformspartoftheneck&
themusclesfromtheheadpassdirectlytotheacrotergiteofthe
mesothorax.
Anareaatthebackofeachsegmentremainsmembranous,forminga
newintersegmentalmembrane.
Thisbasicconditionwithamembranousareaattheposteriorendofeach
segmentoccursintheabdomenwherethisissclerotized,inthemeso
andmeta-thoracicsegmentsoflarvalinsectswithasclerotizedthorax.
IntheApterygotaandinadultBlattodeaandIsopterawherethewings
arenotmovedbyindirectmuscles

9. SUTURE OF TERGUM, STERNUM AND
PLEURON

10. TRANSVERSE STRUCTURE OF AN INSECT THORAX:

11. 1.TERGUM
Thetergumoftheprothoracicsegments-pronotum.
Prothoracictergumisanundividedskeletalplate.
Tergumissimpleinwingless/immaturewingedinsectsandmodifiedin
wingedinsects.
Inwingedinsectsthetergumdividedinto2parts-
a)Alinotum:anterior,wing-bearingportion,
-internallybearsanteriorphragma(antecosta)
a)Postnotum:posteriorportion,wingless;
-bearsposteriorphragma-modifiedforwingsupport
Notumofwingbearingsegmentsisdividedbytransversesutures.
Theyaretheprescutum,scutumandscutellum.

12. Fig. Tergum and there sutures

13. 2.STERNUM
Theprimarysclerotizationsonventralsidearesegmentalandintersegmental
plateswhichoftenremainseparateinthorax.
Theprosternumresembleswithsternaofthepterothorax.
Thesternumofanythoracicsegmentiscomposedofasegmentalplate,the
eusternumandthefrontalintersegmentalsclerite,spinasternum.
Eusternum:Largeanteriorplate,dividedinto3sclerites,thepresternum,the
basisternumandthesternellum.
Sternocostalsuturewhichseperatesbasisternumfromthesternellum.
Spinasternumcalledaspoststernellum,smallerposteriorplate
Spinaandfurcaprovideareasforattachmenttoventrallongitudinalmuscles.

14. Fig. Sternum region of insect thorax.

15. Fig. Sternum and there suture

16. Basisternumisbigger,providingforattachmentofthelarge
dorsoventralflightmuscles.
Sternumisattachedtopleuronbypreandpost-coxalbridges.
Arisingofeusternumareapairofapophysescalledassternal
apophyses.
Theoriginsoftheseonsternumaremarkedexternallybypits
joinedbyasulcus.

17. Inhigherinsects,twoapophysesarisetogetherinmidlineand
onlyseparateinternally,formingaY-shapedfurca.

18. 3.PLEURON
Pleuralregionsaremembranousinmanylarvalinsects,buttypically
becomesclerotizedinadult.
Consistsofthreesclerites;oneventral,thesternopleuriteandtwodorsal,
theanapleuriteandcoxopleuritewhichmayoriginallyhavebeenderived
fromcoxa.
Sternopleuritearticulateswithcoxa.Itisfusedwithsternumandbecomes
itsintegralpart.

19. Theanapleuriteandcoxopleuriteareseparatedfromoneanotherinthe
ApterygotaandlarvaeofPlecoptera.
Intheadultpterygoteinsects,theyfusetoformacommonpleuron.The
coxopleuriteoritsanteriorremnantsremainpartiallyseparatedinlower
pterygoteinsects.
Intheseinsectstheyformadistinctsclerite,trochantinasanadditional
ventralarticularscleriteforarticulationwithcoxa.
Stonefly

20. Fig. Pleuron and there suture

21. Inhigherinsects,trochantinmayreduceorfusewithlowermarginof
episternum.
Trochantin and coxal articulationis used as in many cases, important for
leg movements.
Pleuron of the pterothoracic segments is divided by a pleural suture which
extends from pleural ring process onward to pleural coxal process into two
pleurites;
a)Anteriorepisternum
b)Posteriorepimeron.

22. Pleural suture: internally forms Pleural ridge
-Gives strength to pleuron
-Bears Pleural apophyses in winged segments
-Arm like projection directed ventrally, associated with a Sternal
apophyses
Insomeinsects,episternaandepimeraaredividedintotwopartsbya
transversesuture.