INSECT HORMONES

Manduca sexta Rhodnius prolixus

Main Endocrine Centres Neurosecretory cells in brain Brain Neurosecretory cells in SEG Prothoracic (ecdysial) gland Corpus cardiacum Corpus allatum Neurosecretory cells in VNC Ovary

Neuroendocrine Regulation Central nervous system Neurosecretory cells +/- +/- +/- Hormone • • • • • • • • • • • • Neurohormone Neurohemal organ +/- Neurohormone Endocrine gland +/- Hormone Target cell +/- Target cell

Physiological Actions of Hormones 1. Metabolism and homeostasis * Metabolism of carbohydrates, lipids * Water balance and diuresis (excretion of water following a blood meal) * Cardioactive and muscle stimulation/inhibition 2. Growth, molting and metamorphosis 3. Reproduction 4. Diapause = state of arrested development * Any stage - egg, larval, pupal, adult 5. Phase or caste polymorphism * Social insects - ants, termites, honeybees * Locusts and aphids show phase polymorphism 6. Behaviour * During molting process * Migration * Reproductive behavior * Social behavior * Pheromones

Sensitive periods for JH JH level Ecdysone level 4th instar 5th instar

Moulting and Hormones Outer epicuticle Epicuticle Inner epicuticle Exocuticle Procuticle Endocuticle Epidermis Basement membrane Pore canals

Moulting Cycle (Part 1) Step 1 Step 2 Step 3/4

Moulting Cycle (Part 2) Step 5-7 Ecdysis New Integument

Insect Moulting 2 1 3 4 OLD 5 epi- exo- endo- epithelial cells subcuticular space moulting fluid epi- OLD exo- 3 Ecdysial membrane New epicuticle- Undifferentiated procuticle 4 Cuticlin layer 5 Epithelial cells

Ecdysone Juvenile hormone I Juvenile hormone II 20-Hydroxyecdysone CH3 CH3 CH3 CH3 O CH3 CH2 CH2 CH3 C H C CH2 CH2 O C H C C O CH3 CH3 H Ecdysone CH3 Juvenile hormone I CH3 O CH3 CH2 CH2 CH3 C H C CH2 CH2 O C H C C O CH3 H CH3 Juvenile hormone II CH3 O CH3 CH2 CH2 CH3 C 20-Hydroxyecdysone H C CH2 CH2 O C H C C O CH3 H Juvenile hormone III

(neurosecretory cells) Action pathway for JH and Ecdysone Brain (neurosecretory cells) Production, storage and release of protothoracicotropic hormone (PTTH} Corpus cardiacum Corpus allatum PTTH stimulates Juvenile hormone (JH) Binding protein (JHBP) Ecdysone (ec) JH-JHBP 20-hydroxyecdysone chromosomes chromosomes chromosomes RNA RNA RNA Protein synthesis Protein synthesis Protein synthesis Larval structures Larval structures Larval structures

Moulting video http://www.vanderbilt.edu/exploration/news/news_bursicon.htm