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Pupa mystery

A demonstration to show how insects use hormone to co-ordinate metamorphosis.
Useful information
Kit List: 

10 tubes containing the maggots.
The pictures of the maggots and lifecycle of flies.
Pictures of human endocrinological diseases - diabetes, increased and decreased growth hormone, hypertestosteronism.


*** OVERVIEW ****

(Warning: Quite advanced) A demonstration to show how insects use hormone to co-ordinate metamorphosis.

Possible activities:
1. Verbal description of the material. Lifecycle of an insect. How development is controlled by hormones.

Other things to talk about:
1. Hormones in humans
2. Insects can survive gross mutilation of their bodies.
3. Some plants make very potent form of insect hormones for defence.

Tips for demonstrating: This is quite difficult, not for the very young.


Ask them whether they know what a maggot is. Explain the lifecycle of the fly.

Explain the concept of communication and hormone in insects.

Depending on the age, explain to/ask the child why tying a string to the maggot would stop the hormone from spreading. Show them the specimens.

Show + explain the specimens that are tied too late (hence both sides become pupa)

Show + explain the 'tied up both end' specimen. (Oxygen/air is needed for the pupa to turn red, tying a string at both ends cut off air supply)

This is quite difficult, not for the very young (you have to decide on the day). But to avoid accusing someone's child is stupid, explain it to their parents instead.

Make it simple. Associate it with situations which are familiar to the child (e.g. explain the concept of communication by saying: if you want your mum to get you a glass of lemonade, you'll shout: 'Mum I wanna lemonade'. In the same way the brain of the maggot need to tell the rest of the body...)

If the kid is old enough, ask them to try to figure out what is going on. Explain the lifecycle of the fly and show them the half maggot half pupa specimen and ask them 'why does this happen?'


Insecty Stuff:

Insects can survive gross mutilation of their bodies! Decapitated larvae of many insects can survive for over a year under sterile conditions. (Indeed scientists used to stick decapitated larvae to an adult and see what happens to the adult.

Some plants make very potent form of insect hormones, so that when insect larvae (caterpillars, for example)eat the leaves they will die because they will moult too early - imagine your skin falling off after eating cabbage!

Human Stuff:

Humans also use hormones to co-ordinate growth and other body processes (insulin, adrenaline, etc). Look at the pictures of endocrinological diseases. Ask a medic for some help if you get stuck on this. Extra info to help you, the demonstrator know a bit more about what you're talking about!


No-one really knows what causes type one (juvenile onset) diabetes. Problem is autoimmune destruction of pancreatic islet cells which produce insulin. Problem in type two (which is associated with increased age and obesity) is that the body becomes "insulin resistant", ie. the receptors for it don't respond as well as they should. That last fact's probably easier to explain to older kids or parents. Pre-diabetes (insulin resistance) is where the receptors are heading in the direction of being unable to respond to insulin.
If cells can't take in glucose via insulin-mediated pathways they become starved. Meanwhile the patient's blood is full of sugar. This is what makes you drink a lot, because sugar is sucking all the water out of your cells. Untreated diabetes, certainly, type 1, is fatal. The person goes into a coma due to the brain running out of glucose.
Treatment -
Inject insulin in type 1. Type 2 might be controllable by dietary means - cutting down on sugar means that the cells don't have too much sugar to deal with. Severe type two diabetes needs insulin injections (the cell receptors can respond to high concs of insulin). Blood pressure control is essential in type two diabetics to prevent heart attack and stroke. Type one diabetics have to monitor their blood sugars very carefully using portable kits so that they can titrate their insulin properly.
Kids may know that their diabetic friend is meant to carry around something sugary eg. lucozade tablets at all times. this is in case they give themselves too much insulin and end up hypogylcaemic - they feel dizzy and strange t this point and it can be quite dangerous.

Growth hormone

Aetiology and Pathogenesis -
GH Comes from anterior pituitary (along with FSH, LH, ACTH, TSH and Prolactin - "FLAT P(I)G" - best mnemonic I ever learned!). Decreased production is usually noticed if it occurs in childhood because it affects the child's growth (which we measure at fairly regular intervals in the UK on growth charts) from around 1 year. This is when growth is more dependent on GH and less on calorific intake (calories matter between the agew of 0 and 1). GH becomes less important when the growth hormones, particularly oestrogen (though you wouldn't have thought it) take over in the teens.
Decreased GH production is the most common hormonal deficiency to occur at the anterior pituitary. It can happen from birth due to malformation of the pituitary, or it can be caused by things pressing onto the pituitary, eg. tumours, tubercolosis infection, or trauma to the skull.
Increased GH production ("GH excess") usually occurs because of pituitary adenomas. Causes giantism in the young (before fusion of bony growth plates) and acromegaly in older people (square jaw, spade-like large hands - the bones are growing - and an enlarged tongue).
Treatment -
replace GH if it is lacking, remove the cuase of the problem if it is a tumour or Tuberculosis.


We all know this is a steroid which increases muscle bulk (by being anabolic) to help cyclists out. Other actions of testosterone include - the features of puberty - maintenance of gametogenesis; in the male the final maturation of spermatids to spermatozoa requires the action of testosterone on the Sertoli cells.
High testosterone levels in females may be familial, may be because of drugs or Cushing's Syndrome (where the adrenals make too much steroid hormone), but are frequently due to Polycystic Ovarian Syndrome. This causes, as well as hirsuitism, increased waist size, acne, and lowered voice, disturbed menstural cycles and decreased fertility. it is pretty common with up to 1 in 9 women affected.
Aetiology -
PCOS seems to be linked to insulin resistance, and so occurs to people who are at risk from type 2 diabetes. Insulin resistance leads to increased insulin production. however, it seems that in PCOS, the woman's oavries are very insulin sensitive. The insulin senstivity makes the ovaries go into overdrive and produce testosterone. So it is thought anyway.


Insects that undergo complete metamorphosis will go through the following stages:
Egg - larva - pupa - adult.

The growth of the insect at larval and adult stage is regulated by hormones secreted by the insect's endocrine system. In this experiment we will concentrate on the larval stage.

Larva of the blowfly (which is used in this experiment) hatches from the egg and starts feeding and growing. It will undergo several stages of moulting and after its final moult it will form a pupa. "The larva would stops feeding; the crop (digestive system) would become gradually emptied and reduced... then pupation starts. About 2 hours before pupation, the external appearance of the larvae becomes changed. Up to this time the skin looks shiny, it then become matt white. The movement gradually slacken and the shape becomes relatively shorter and broader... The act of pupation itself is a very complicated process, consist of different reactions...

1) The well-known barrel shape of the pupa is assumed (white pupa)
2) Within a few hours the skin (cuticle) becomes hard
3) At the same time the skin darkens"
(Fraenkel. G. March 16 1935)

The hormone that causes the larva to enter the pupa stage is released from the larval brain (shown on the display as g) and it diffuses through the body fluid of the larva. Once the hormone is released and reached the tissue, there is no going back! This is proven by the experiment - if the ligature is tied before the release of the hormone, it prevents the posterior half from pupating (below left); if the ligature is tied after the hormone is released, the posterior half pupates (below right).

So what about the "Tied up at both ends" specimen? Well, the hormone has been released when the ligature is tied, since both the anterior and posterior ends have pupated. The middle of the larva is actually a white pupa because to form a red pigment of the pupa the larva needs oxygen. The ligature not only stops the flow of hormone it also stops the oxygen from flowing to the middle.

The explanation of the insect hormonal system is a very simplified version. In reality several hormones are released and their interactions are complicated. The hormone ecdysone induces larval moulting when the concentration of another hormone, Juvenile Hormone (JH), is high. The level of JH in the larva declines as it grows, until it falls below a minimum level that causes the next release of ecdysone to induce pupation.

Many other animals (humans included) have endocrine system and many of our bodily processes are under hormonal control: growth (Growth hormone), osmotic control (ADH), menstrual cycle (various hormones such as FSH, LH, progesterone) and blood sugar level (insulin and glycagon)

Risk Assessment
Date risk assesment last checked: 
Thu, 26/12/2013
Risk assesment checked by: 
Risk Assessment: 
DESCRIPTION Looking at dead insect larvae in small sealed tubes, talking about hormonal control in moulting
  1. Smashing a specimen tube can cause cuts, and the preservative to come out. Preservative is 1% Propylene phenoxetol, which should not be irritant to eyes or skin at that concentration, but which may be harmful if ingested.
  2. Child getting injured by the display board, if it is not being used on the floor.
  1. Keep a careful eye on the tubes. If necessary, reduce the number of tubes on display. Make sure all are tightly closed with sellotape on top of the seal to make it obvious that the tube should not be opened. Demonstrator must know the location of the nearest eyewash.
  2. Make sure board is firmly attached to the desk, if not on the floor
  1. Call first aider in case of injury. Wash skin with that has come into contact with preservative with and water. If preservative gets into eyes call a first aider. Use eyewash to wash out of eyes if trained and confident to do so.
  2. Unless large quantities ingested, recommend that parents take child to GP if child becomes ill, and state that 1% propylene phenoxytol was the substance ingested.