1. Animal Physiology and Development Insects – 1 JCS
Lecture Outcome:
At the end of this lecture students should have:
Understood the three different types of insect life cycles and the nomenclature of different developmental stages.
Appreciated the importance, structure and properties of the insect cuticle
Been reminded that as arthropods insect growth requires a series of moults.
Seen the details of the moulting process and learnt how it is controlled by hormones.
JCS 30/10/02

2. Insect life cycles A B C A: Ametabolous – primitive (Apterygota)
B: Hemimetabolous
C: Holometabolous

3. Holometabolous - Diptera
Egg – embryo(genesis)
Larva – 3 instars
Puparium
Prepupa  Pupa
Adult - IMAGO

4. Insect cuticle Waxy layer Epicuticle Exocuticle ] Procuticle
Endocuticle ]
Subcuticular space
Epidermis
Basement membrane

5. Keratin
Chitin
Chitin myofobril

6. Resilin – elastic polymer
relaxed
stretched
polyphenols

7. Cuticle apolysis, deposition and ecdysis

8. Kopec’s experiments on gypsy moth caterpillars
Conclusions:
A hormone secreted by the brain is necessary for pupation
The brain hormone acts between the seventh and tenth day of the last instar.

9. Brain control of moulting
Brain target is the prothoracic gland
Hormone - PTTH prothoracotropic hormone
PTTH is made in the neurosecretory cells and transported to the corpora cardiaca and corpora allata by the axons (where it is stored before release into the blood).
c. cardiaca and c. allata are neurohemal organs

10. Ecdysone the moulting hormone

11. Ecdysone titres and moulting (ecdysis)
Schistocerca gregaria (locust) – hemimetabolous
Manduca sexta (tobacco hornworm) – holometabolous
E = ecdysis, W = wandering larva, PP = prepupa
Radioimmunoassay; NB log scale

12. Juvenile hormone
Moult can lead to:
larva
pupa
adult (imago)
JH titre, secreted from the corpora allata determines the nature of the moult.
JH is neither a sterol or a peptide (typical hormone molecules). It is a terpene