Since hardened cuticle does not permit increase in body size or change in forms of insects during life cycle , shed there old cuticle several times and synthesize new one that are soft and flexible initially to allow for expansion, but subsequently harden to a tough exoskeleton by the process of tanning or Sclerotization.(chapman, 1975) Sclerotization is not necessarily accompanied by pigmentation but tanning is always associated with pigment production. It is nothing but cross links between the proteins of cuticle.

1. Good
morn
ing

2. M.RAMAIAH
RAM/16-39

3. Contents
 Introduction
 Structure of Integument
 Moulting process
 Terms related to insect cuticle
 Tanning / Melanization and Sclerotization
 Types
 Plasticization and Examples
 Conclusion
 References

4. Introduction
The integument is the outer layer of the insect body,
comprising the epidermis and the cuticle.
The cuticle is a characteristic feature of arthropods and is
to a large extent responsible for the success of insects as
terrestrial animals.

5. Insect Integument (Exoskeleton)
1
10
100
1000
10000
100000
Carbon
nanotubes
Graphite fibres Kevlar Steel Chitin Bone
Tensile strength of sclerotized chitin (sclerotin)
kg/mm2
kg/mm2
Tensile strength of sclerotized chitin (sclerotin)

7. Summary of Moulting:
Step 1: Apolysis -- separation of old exoskeleton from epidermis
Step 2: Secretion of inactive moulting fluid by epidermis
Step 3: Production of cuticulin layer for new exoskeleton
Step 4: Activation of moulting fluid
Step 5: Digestion and absorption of old endocuticle
Step 6: Epidermis secretes new procuticle
Step 7: Ecdysis -- shedding the old exo- and epicuticle
Step 8: Expansion of new integument (plasticization)
Step 9: Tanning -- sclerotization of new exocuticle

9. Terminology related to cuticle
 Apolysis
 Ecdysis
 Stadium
 Instar
 Exuviae
 Melanization or Tanning
 Sclerotization
 Burcicon and eclosion hormones.
 Cuticular proteins
 Multiple barrier concept – Richards (1957)

10. Research on
 Among the types of cuticle so far studied, the pupal
cuticle of Manduca sexta has served as a useful model for
investigating sclerotization and the cross-link structure of
hard brown cuticle.
 Puparial cuticles of Diptera and the stiff colourless cuticle
of migratory locusts also have been extensively studied
as models for other types of sclerotization.

11. How tanning differs from
sclerotization
 Since hardened cuticle does not permit increase in body size or
change in forms of insects during life cycle , shed there old cuticle
several times and synthesize new one that are soft and flexible
initially to allow for expansion, but subsequently harden to a tough
exoskeleton by the process of tanning or Sclerotization.(chapman,
1975)
 Sclerotization is not necessarily accompanied by pigmentation
but tanning is always associated with pigment production.
 It is nothing but cross links between the proteins of cuticle.

12. Three modes of crosslinking
1.Quinone tanning.
2. β – sclerotization.
3.Quinone methide sclerotization.
Two main types of sclerotization
quinone tanning - widespread way of tanning - it is generally accompanied
by the darkening of the cuticle (melanisation) - proteins are linked to the rings
β-sclerotization - cuticle remains bright - proteins are linked to the side-
chains

13. Quinone tanning
Sequence of steps in hardening of cuticle
 Tyrosine
 Dopa -dihydroxy phenylalamine
 Dopamine
 N – acetyl dopamine
 quinone protein

14. Integument of insects
Summary of the quinone tanning process

15. (Chapman.R.F,1998)

16. (Andersen S. O.)

18. Fig. 16.8. Amounts of sclerotization of the cuticle from different
parts of the body of a mid fifth-stage larva and a 10-day-old adult
locust. (chapman, 2014)

19. (Chapman, 5th edition 2014.)

20. (Andersen S. O)

21. Plasticization
 Expansion /streching of the new cuticle.
 Resilin and procuticle
 Hormones involved – Eclosion hormone and bursicon
 Ecolosion hormone-before ecdysis
 Bursicon hormone- after ecolosion
 How it occurs?

22. (Chapman R. F, 2014)

23. Plasticization in female grass hopper/locust
 The inter segmental membrane
between abdominal segments
4 and 5, 5 and 6, 6 and 7 is made
up of elastic cuticle.

24. Plasticization in blood sucking bug
 The abdomen increases about four – fold
and cuticle become thinner.
 CNS
 Serotonin hormone
 pH change in the cuticle from 7 to below 6.
 Water content increases from 26% to 31%
 Decreasing hydrogen bonding.
 Plasticization is reversible.

25. Cuticular plasticization in blood
feeding mosquito
 Occurs as a result of the action
of hormones or neurohormones.
 Female Aedes triseriatus,
feeding."The treehole mosquito
(Aedes triseriatus) transmits
the virus that causes La Crosse
encephalitis." Courtesy CDC

26. Extent to which a region on a dorsal sclerite of a fly can be stretched.
1. During digging the cuticle is inextensible.
2. Reaches the surface and swallows air to expand new cuticle.
This causes release of bursicon.
3. Cuticle now becomes sclerotized and inextensible.

27. Fig. 16.7. The relationship between sclerotization and cuticular
stiffness. Over the period of the molt, and principally around the
time of eclosion, the degree of sclerotization of an abdominal
tergite of the honeybee increases. (Chapman, 2014)

28. Membranous connection of two sclerites forming a membranous
area. Which layer of the cuticle is lacking or minimal for the
membrane area.
Why is this so?

29. Transverse section through the thoracic wall and wing base of a
grasshopper showing the position of the wing hinge (figure on left).
On the right is an enlargement showing the resilin pad.

30. Conclusion
 Integument act as protective layer.
 Tanning helps to insects in darker areas.
 Plasticization helps to insects like locust, blood sucking bug etc.
 Sclerotized areas usages like flight and cutting.
 One major goal which is completely negleted at present is the finding
of suitable and highly effective inhibitors for sclerotization.
 Such inhibitors can effectively be used as new insecticides in future.

31. References
 Chapman R. F. 2014. The Insects: structure and function.
Cambridge university press.lec – 16, 463 – 499.
 Gour, T.B and Sriramulu, M. 2004. Insect Physiology principles
and concepts. Kalyani publishers, Hyderabad.lec-1,1-19.
 Wrigglesworth V. B. 1974. Insect physiology. Toppan
company.lec – 1, 1 – 13.
 Saxena R.C, Srivastava R.C and Somani L. L.. 2004, Entomology
at a glance. ATPA.volume – 1, 46-52.
 Advances in insect physiology edited by Evans.1998.
(M. Sugumaran, Unified mechanism for sclerotization of insect
cuticle , volume 27., page no, 229 to 324.)