The cuticle Flashcards
Cuticle structure
From haemolymph to outer surface of environment:
- Basal lamina - sheet of connective tissue which lines exoskeleton
- insect blood in contact, 5 microns thick - Epidermis - columnar epithelium (cubic rectangular shape)
- maintains and manufactures cuticle, nerve cells permeate layer - Pro-cuticle of 2 parts
- Epicuticle - very thin but most complex
Epicuticle parts
Starting on top of exocuticle…
- Inner epicuticle
- Outer epicuticle
- Lipid monolayer (in all insects)
- Superficial layer
- Cement layer
- pore canals run from epidermal cells into surface of epicuticle
Pore canals
•material produced in epidermal cells are carried through these to epicuticle
•pore diversify in the inner epicuticle = wax canals
-forms a waxy blood on outside of cuticle - in scale insects especially
-wax crystals on outer surface prevent parasitoids
Cement layer of Epicuticle
Cement - holds all layers together and maintains integrity
•made of shellac-like proteins which is a resin, very brittle
Lipid monolayer of Epicuticle
•forms a lipid sheet - single layer of fat molecules which provide water-proof coating
•hydrophobic on outside and hydrophilic facing haemolypmh
•hydrophilic parts lock closely together
•when warmed, hydrophilic ends face upwards more and are more likely to form gaps which allow water molecules through when big enough
=waterproof till certain temp, past monolayer breaks down
Heat chamber experiment
By Wrigglesworth:
•heat chamber with balance inside
1. Dead insect inside and heated up
2. Looked at changes in weight
Found after heating for a while lost weight massively
•molecules line themselves more vertically and gaps form, opening more causing the insect to lose water
Procuticle
Made of two parts where the ratio and actual thickness varies a lot between species and parts of the insects body
- Exocuticle (on top - closer to outside)
- Endocuticle (on bottom)
Exocuticle
- thickness varies - when stiff cuticle is needed, its thick (e.g. mandibles of locusts)
- non-existent in pleural membranes and if need mobility
- is the layer that is shed as it cannot be recycled (due to crosslinks)
2 main processes of making the cuticle hard:
- Melanisation - makes cuticle hard and darker (eumelanin is lighter than phaeomelanin)
-crosslinks make cuticle stronger - Sclerotisation - crosslinks without affecting colour - useful over compound eyes where needs to be transparent
•some places have combination
Other things that make the cuticle hard?
•can be made very strong by incorporating filaments of chitin, very tough and strong already - reinforced by chitin
-process called tanning
•micro-fibres of chitin will be incorporated parallel to one another
-different layers put at different orientations by circadian clock changing direction as layers secreted
-makes even more strong and tough
Endocuticle
•flexible areas will be only endocuticle (makes pleural membranes)
•flexible and transparent - no melanisation etc.
•incorporates resilin - novel to insects
-found in wing hinges of insects (allows fleas to jump, energy storage in pure resilin)
-99.9% efficient, will always return to original state
•incorporated in hinges and springs
•not cross-linked can be recycled
Moulting process
- Nuclei and cells get larger in epidermis
- Exuvial space forms between old cuticle and epidermis
- Space filled by moulting fluid (secreted by epidermis)
- inactive and new cuticle secreted - Ecdysial membrane forms between active and inactive fluid (stops new being digested)
- Useful substances from old recycled and new part secreted is the procuticle
After new cuticle has been secreted
A newly moulted insect is white and soft, due to procuticle not being differentiated yet.
Over next 24hrs chemicals are secreted into procuticle allowing specialisation and differentiation of endo and exo
Function of the cuticle
- Mechanical protection - support
- Provides surface for muscle attachment
- Water retention and conservation
- Location for colours - lots of pigments in camouflage, courtship and aposematism
- Active barrier against pathogens - and pesticides
