INSECTS II

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INSECTS II
What stages of life do insects go through? How do
caterpillars relate to butterflies? Larvae,
Nymphs Adults Exoskeletons
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Stages of Life

• Incomplete metamorphosis an egg becomes a
  nymph, which evolves gradually into an adult.
• Complete metamorphosis an insect progresses
  through several distinct stages egg to larva to
  pupa to adult.

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Incomplete metamorphosis
Nymphs and adults eat the same food and live
in the same surroundings.
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Complete Metamorphosis
Larvae and adults may eat different foods, thus
avoiding competition for a single resource.
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The Life Cycle of a Butterfly

• The first stage is called the egg stage. The
  mother butterfly lays eggs on a leaf.
• In the larva (2cd) stage, the egg hatches on the
  leaf and out comes a caterpillar.
• In the pupa (3rd) stage the caterpillar grows and
  it pops out of its old skin, already wearing a
  new one.
• The adult (4th) stage is also called the Imago.
• The Imago (5th) stage begins when the chrysalis
  is broken and the butterfly breaks out.

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The Larva Stage

• The caterpillar grows and it pops out of its old
  skin, already wearing a new one four or five
  times, after which the caterpillar begins to
  produce silk. With this silk, it attaches its
  body to a leaf or twig. It then sheds its furry
  skin for the last time. Under the skin is a hard
  form called chrysalis. The caterpillar's body
  turns to a soft liquid, from which the wings,
  legs and other body parts of the butterfly will
  form.

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Exoskeletons I

• An insect's exoskeleton serves as a
• protective covering over the body
• a surface for muscle attachment
• a water-tight barrier against desiccation
• sensory interface with the environment

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Exoskeletons II

• Composed of overlapping, hardened plates, with
  membranous areas between the plates, for maximum
  strength with flexibility
• Good at reducing water loss to the environment,
  which is critical for a small organism with a
  large surface area to volume ratio

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Exoskeletons III

• The exoskeleton is composed of chitin surrounded
  by a matrix of protein that varies in composition
  from insect to insect
• Our fingernails are composed of chitinthe same
  material in an insects exoskeleton!

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Molting I
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Molting II

• The destruction of old cuticle, formation of new
  and larger cuticle, and shedding of remnants of
  old cuticle.
• Old cuticle is partially used to make new one.
• Newly molted insect appears whitish, since no
  color in cuticle. They are NOT albinos.
• New cuticle tans (like a hide), hardens, and
  takes color in short time.

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Molting II continued..
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Controls of Molting

• Controlled by endocrine system, and by brain.
• Gut receptors, elsewhere indicate stretching.
• Cells in brain secrete hormone that stimulates
  prothoracic gland. This gland produces a molting
  hormone called ecdysone.
• Molting controlled by brain and prothoracic gland
  in prothorax.

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Sources

• 1. Insects and Human Society
• http//www.ento.vt.edu/ihs/distance/lectures/abun
  dance/abundance_slide04.shtml
• O. Orkin Insect Zoo
• http//insectzoo.msstate.edu