Integument, Molting and Endocrine Control Flashcards
What are the major constituents of an insect cuticle? (2)
- Chitin
2. Proteins
What is lamellae?
A polymer chain of N-acetylglucosamine that are bound by proteins to form sheets
How is the cuticle made unstretchable?
Lamellae are laid down at different angles every half hour
How much of the chitin in the cuticle is reabsorbed during molting?
about 85%
Where are proteins found in the insects cuticle?
Cross-linked to lamellae
What are the layers of the cuticle from the outermost layer to innermost layer? (4)
(Outermost) - Epicuticle - Exocuticle - Endocuticle - Epidermis (Innermost)
What is the function of the Epicuticle?
provides a waterproof layer for the insect and prevent water loss
What is the function of the Exocuticle?
Forms a protective shell (hardened by sclerotization
What is the function of the Endocuticle?
To be reabsorbed during molting. Not sclerotized
What is the function of the Epidermis?
To produce all the layers of the Integument. Only actual living part of the integument
How is wax formed on the Epicuticle and why?
A gland in the epidermis extends all the way up to the top most layer to create the wax covering in order to prevent water loss and waterproof the insect
What are the three stages of molting? (in order)
- Apolysis
- Ecdysis
- Sclerotization
What is Apolysis?
The separation of the epidermis from the cuticle of the previous stage
What is Ecdysis?
The casting off or escape from the residual cuticle of the previous stage. There is a fully formed insect inside the old cuticle prior to this stage
What is Sclerotization (in regard to molting)?
A chemical process that hardens the outer section of cuticle (exocuticle) after ecdysis by cross-linking cuticular proteins with oxidized phenols.
occurs from the outside in.
What is a pharate?
The fully formed insect inside the old cuticle prior to ecdysis
What is an exuvium?
The cast off cuticle after ecdysis
What is a teneral adult?
An insect that has not finished sclerotizing its integument after molting
What are the 6 stages the cuticle goes through during molting?
- Apolysis
- Production of cuticulin
- Digestion of endocuticle
- Resorption of molting fluid
- Cuticle immediately after Ecdysis
- Mature cuticle
What hormone controls sclerotization?
bursicon
What are the two types of sclerotization? Which is light and which is dark colored?
- Quinone Tanning - Dark colored
2. Beta-Sclerotization - Light colored
What are some unsclerotized parts of an insect?
the intersegmental membranes, the joints and appendages
What is sclerotized in a holometabolous larvae?
The head capsule, mandibles and true legs
What does ecdysis depend on in many species?
Blood pressure and/or air pressure
How is ecdysis performed in many insects?
Insect contracts abdomen for a prolonged period of time which forces blood into the head and thorax. can be assisted by swallowing air
What is ecdysis often aided by? How?
Aided by gravity
- insect hangs upside down, secured by claws of the hind tarsi. Rupturing of the ecdysial cleavage line on the head capsule allows the insect to slide out of the exuvium
How does the muscid fly perform ecdysis?
They have a specialized structure on the head, the ptilinum, an inflatable bladder that breaks open the puparium and allowing the adult fly to emerge
What do insects often have to do after ecdysis? why?
- Swallow air or contract specific muscles to facilitate expansion of the new cuticle prior to sclerotization.
- Pump blood to wings to make sure they are fully expanded
In some species, what must be done throughout the sclerotization process?
Muscles of the abdominal wall must remain contracted throughout
Why are insects especially vulnerable to predators during molting?
They need to remain motionless during sclerotization and have a weak state of cuticle prior to and during the process
What are 5 hormones involved in the control of molting?
- Juvenile hormone
- Ecdysone
- Prothoracicotropic hormone (PTTH)
- Eclosion hormone
- Bursicon
What role does the juvenile hormone play in molting?
determines the course of development
What role does Ecdysone play in molting?
Stimulates the molting process (Ecdysis and Apolysis)
What role does the Prothoracicotropic hormone (PTTH) play in molting?
Stimulates the release of ecdysone (stimulates prothoracic gland to synthesize and secrete ecdysone)
What role does the Eclosion hormone play in molting?
triggers molting behaviours including stereotyped sequence of behaviours involved in adult emergence from the pupa
- also stimulates release of bursicon
What role does Bursicon play in molting?
Stimulates sclerotization of cuticle
- increases permeability of epidermal cells to dopamine
- stimulates conversion of tyrosine to dopa
Describe the endocrine control of molting and development (in order and including hormone names for each step)
- PTTH stimulates Ecdysone synthesis and release
- Ecdysone tiggers molting
- JH titre determines the outcome of the molt
Where is the juvenile hormone synthesized?
In the corpora allata glands
What does the juvenile hormone act on?
Acts directly on the epidermis and internal tissues
When does juvenile hormone occur and in what levels throughout the insects life?
- Occurs throughout larval stages in gradually decreasing levels.
- Disappears during final instar except for a brief peak just prior to pupation.
- Reapears in adult stage to regulate reproduction
What happens to Juvenile hormone when it is made?
It is not stored, it is released as synthesized.
What are titres determined by with regard to juvenile hormone?
rate of degradation by specific JH esterases produced in the fat body
What is Ecdysone synthesized from?
Cholesterol or plant sterols obtained from the diet
What is ecdysone synthesized by?
The prothoracic gland
What is a substitute for ecdysone and what insects use it?
Makisterone-A
- used by some hemipterans and the honey bee
What type of hormone is the prothoracicotropic hormone?
A polypeptide
What is the prothoracicotropic hormone produced by?
Specific groups of medial neurosecretory cells in the brain
How is the prothoracicotropic hormone transported and what happens to it after it is synthesized?
Transported by nerve axons to the corpora cardiaca glands where it is stored
How is the eclosion hormone released?
Released by a circadian clock
Where is the eclosion hormone produced?
In the brain and abdominal ganglia
Where is the Bursicon hormone produced?
in the perivisceral organ
How do plants mimic Juvenile hormone?
Produce a number of secondary compounds that have JH-like bioactivity in insects
- also produce anti-JH compounds
