2. CONTENTSCONTENTS
Advantages of an exoskeletonAdvantages of an exoskeleton
Insect growth and developmentInsect growth and development
Strategies for growthStrategies for growth
Instars, stadia, and hidden phasesInstars, stadia, and hidden phases
Structure of the integumentStructure of the integument
Modified features of the integumentModified features of the integument
Chemistry of the cuticleChemistry of the cuticle
The molting processThe molting process
Endocrine control of moltingEndocrine control of molting
Endocrine control of metamorphosisEndocrine control of metamorphosis
Metamorphosis and the radically changing cuticleMetamorphosis and the radically changing cuticle
3. Insect IntegumentInsect Integument
Insect integument system – exoskeleton
– like the skin of vertebrates - provide a barrier to
the environment
water (*high surface-to-volume ratio)
ions
parasites
environment chemicals, including pesticides
– as the skeleton system in insects - allow for the
insertion of muscles to locomotion
– as food reservoir (???) / molting & starvation
– mating recognition - responsible for releasing
particular behavioral sequences
– many other functions
4. Insect IntegumentInsect Integument
Advantages
– significant mechanical strength over an
endoskeleton of the same weight
(next slide)
Disadvantages
– restrict insect growth - molt
– molting is dangerous to insects
– molting consumes time, energy, and
metabolic resources
5. Insect Growth and DevelopmentInsect Growth and Development
The growth and development of insects
are largely a function of the growth and
development of their integuments.
– Molting
– Metamorphosis
6. Strategies for GrowthStrategies for Growth
Metamorphosis: the change that occurs as an
insect develops from an immature to an adult;
separates and early feeding stage from a later
reproductive stage.
– Ametabolous development - continue to molt as
sexually mature adults and there is no real
metamorphosis
– Hemimetabolous (incomplete) development -
immatures lack wings and genitalia (exoptergotes)
– Holometabolous (complete) development - a
sometimes very radical change in form and ecological
habits between immatures and adults
(endopterygotes)
7. Three Major Types of Metamorphosis in InsectsThree Major Types of Metamorphosis in Insects
8. Instars Stadia and Hidden PhaseInstars Stadia and Hidden Phase
Instars: a term to describe an immature insect between
ecdyses
Stadium: a term to describe the length of time spent
between ecdyses
Pharate instar (adult): a term to describe an insect within
the loosened, but not yet shed, cuticle
9. Structure of the IntegumentStructure of the Integument
The outer covering of insects is referred to both as an
exoskeleton and an integument.
The integument consists of
– basement membrane
– epidermal cell layer – epidermis
– nonliving cuticle
10. Structure of the IntegumentStructure of the Integument
Basement membrane: a continuous sheet of
mucopolysaccharide, as much as 0.5 µm in
thickness; initially secreted by hemocytes
Epidermis: the only living portion of the
integument; modifications of these cells produce
dermal glands, sensory receptors and their
support cells, and oenocytes.
Cuticle: secreted by epidermis; divided into two
main regions
– epicuticle: consists of cement layer, wax layer, outer
epicuticle (cuticulin layer), and inner epicuticle
– procuticle: consists of exocuticle, mesocuticle, and
endocuticle, contains largely of chitin and protein
11. The ProcuticleThe Procuticle
The procuticle is secreted by the epidermal cells
and consists largely of chitin and protein. (next
slide)
– exocuticle: the proteins become heavily cross-linked
and insoluble; are not broken down during the molting
cycle; pigments deposited within it
– endocuticle: synthesis continues after the old cuticle
is shed, often in daily layers; cross-linking is reduced;
completely broken down during molting process
– mesocuticle: as a transitional layer in which the
proteins are untanned like the endocuticle but
impregnated with lipid and proteins like the
exocuticle.
12. The EpicuticleThe Epicuticle
The epicuticle is a complex consisting of several
layers that are produced by both the epidermal cells
and dermal glands. (next slide)
– Cement layer: consists mostly of lipoprotein secreted by
dermal glands.
– Wax layer: are mixtures of hydrocarbons with 25-31 carbon
atoms, alcohols of 24-34 carbon atoms, and esters of fatty
acids; produced by the epidermal cells
– Outer epicuticle (i.e. cuticulin): synthesized by epidermal
cells; present in all insects; the first layer of the new cuticle
to be synthesized
– Inner epicuticle: contains both polyphenols and the
enzyme polyphenol oxidase, which involved in tanning the
cuticle.
13. Fig. The relative water loss in two insects as aFig. The relative water loss in two insects as a
function of temperature.function of temperature.
14. Modified Features of the IntegumentModified Features of the Integument
Arthrodial membrane: the flexible membranes
between body segments where the exocuticle is
absent; untanned endocuticle contains special acidic
proteins and resilin (a flexible protein) to provide the
flexibility in the region. (next slide)
Ecdysial line: areas of reduced exocuticle that they are
programmed areas of weakness that serve as
emergence points during ecdyses. (next slide)
Pore canals: cytoplasmic extensions of the epidermal
cells extend from the epidermis through the cuticle to
its surface. (next slide)
17. Chemistry of the CuticleChemistry of the Cuticle
The insect cuticle is composed largely of
– Proteins
comprise more than half the dry weight of the insect
cuticle
primarily located within the procuticle
synthesized mainly by epidermal cells
– Chitin
consisting of 20-40% of the total dry weight of the
cuticle (the other major component of procuticle)
a polymer of N-acetyl-D-glucosamine (-
galactosamine)
synthesized by epidermal cells
– Lipids
mainly located in the wax layer of epicuticle
18. Families of protein in insect
Class C proteins
Class BD proteins
Class H proteins
Class T proteins
Kinds of cuticular proteins
Varies
Heavily sclerotized: hydrophobic, positively charged proteins
Flexible cuticle: acidic proteins (bind water)
R. prolixus, lower the pH of portions of cuticle to below 6
more plastic to expand when blood meal
20. The Steps in the Synthesis of CuticularThe Steps in the Synthesis of Cuticular
Tanning PrecursorsTanning Precursors
(NADA)
(NBAD)
(*less dark than NBAD)
More dark
Less dark
21. Fig. Differences between quinone sclerotization and β-
sclerotization in where the cross-linked proteins are attached.
Catecholamines
phenolosidases
quinones
22. The Molting ProcessThe Molting Process
The molting process involves an elaborate
sequence of events that produces a new
cuticle capable of significant expansion before
the old one is discarded.
The molting process begins with apolysis and
ends with ecdysis.
– Apolysis: the separation of the epidermal cells from
the old cuticle
– Ecdysis: the casting off of the old cuticle
23. The Steps of Molting ProcessThe Steps of Molting Process
Exuvial space: the area between the cuticle and epidermis; fills with
a molting gel that contains inactive enzymes including a chitinase
and proteases for digesting the old cuticle.
24. The Steps of Molting ProcessThe Steps of Molting Process
• The epidermal cells secrete a new outer epicuticle (lipoprotein: cuticulin);
• The activation of the enzyme in the molting gel, now called the molting fluid;
• The molting fluid begin the digestion of the old unsclerotized endocuticle;
• The epidermal cells begin to secrete the new procuticle;
•
25. The Steps of Molting ProcessThe Steps of Molting Process
• Formation of the new epicuticle;
• Absorption of the molting fluid;
• Ecdysis: induced by eclosion hormone.
26. Eclosion Behavior andEclosion Behavior and
Its Endocrine RegulationIts Endocrine Regulation
Behavior of ecdysis are divided into two phases:
(control by central nervous system)
– Pre-ecdysis behavior: loosen the old cuticle through
rotational movements of the abdomen
– Ecdysis behavior: shed the old cuticle by means of
peristaltic contractions
A cascade of neurohormones is responsible for
eliciting eclosion behavior
– Ecdysis-triggering hormone: from epitracheal glands
– Eclosion hormone: from CC
– Crustacean cardioactive peptide (CCAP): from the
ventral ganglion
27. Endocrine Control of MoltingEndocrine Control of Molting
Control of PTTH release
Prothoracico tropic hormone
–nervous stimuli such as stretch
receptors and critical size (or body
mass)
–environmental stimuli such as
photoperiod, temperature
28. Endocrine Control ofEndocrine Control of
MetamorphosisMetamorphosis
Two major hormones are involved in
the metamorphosis
– juvenile hormone
– ecdysteroids
30. SclerotizationSclerotization
CuticularCuticular sclerotizationsclerotization, also known as, also known as
tanningtanning, stabilizes the protein matrix of the, stabilizes the protein matrix of the
cuticle to make it stiffer and harder, morecuticle to make it stiffer and harder, more
insoluble, and more resistant to degradation.insoluble, and more resistant to degradation.
The process of sclerotizationThe process of sclerotization cross-links thecross-links the
functional groups of cuticular proteins whenfunctional groups of cuticular proteins when
they react withthey react with quinonesquinones..
The amino acidThe amino acid tyrosinetyrosine provides one of theprovides one of the
precursors (DOPA or NADA) for sclerotization.precursors (DOPA or NADA) for sclerotization.
The precursors are oxidized byThe precursors are oxidized by
phenoloxidasesphenoloxidases to form reactive quinones.to form reactive quinones.
31. Hormonal Regulation ofHormonal Regulation of
SclerotizationSclerotization
At least two hormone are involved in
the regulation of sclerotization
– Ecdysteroids: induce the epidermal
cells to synthesize the dopa
decarboxylase (to synthesize NADA)
– Bursicon: induced by declining
ecdysteroid titers; increase the
permeability of epidermal cells to
tyrosine and to hemolymph
catecholamines.
34. The OenocytesThe Oenocytes
TheThe oenocytesoenocytes are large polyploid cellsare large polyploid cells
associated with the basement membrane.associated with the basement membrane.
– some oenocytes might be involved in thesome oenocytes might be involved in the
production ofproduction of cuticular lipidcuticular lipid that are depositedthat are deposited
in the epicuticle.in the epicuticle.
– other types of oenocytes may secreteother types of oenocytes may secrete
ecdysteroid hormonesecdysteroid hormones..
