Activity - Growth by Molting

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Activity - Growth by Molting - Articles
Activity - Growth by Molting

Introduction

The hard exoskeleton of insects is very important to their survival. It:

  • allows for structural support of muscles
  • provides physical protection, and
  • gives protection from dehydration.

The outer layer of the exoskeleton has a waxy covering, or cuticle, which keeps moisture in the creature's body. During molting, insects split their old, tight-fitting skins along a weakened area of the back. As they emerge, the insects suck air into their bodies to stretch out the new, flexible exoskeleton underneath as it hardens. This gives them "room to grow" for awhile. During molting, insects are very vulnerable because their bodies are soft. They are susceptible to crushing, dehydration, and they can not move quickly because the muscles have nothing t o work against. Insects must molt from 3-6 times from egg to adult stage. Each stage between molts is called and instar.

Success of molting depends on specific chemical steps which must be completed correctly in the right order. First, levels of hormones "ecdysone" and "juvenile hormone" must be just right. Ecdysone initiates the molting process and juvenile hormone determines the cuticle type and correct next life stage form (larva, pupa or adult). Other complex chemical processes begin the breakdown of the old layer of exoskeleton across a seam in the back and the secretion of the multi-layered new exoskeleton under the old.

Learning Objectives

  1. Understand the importance of exoskeleton to insects.
  2. Learn by demonstration how insects molt.
  3. Discuss ways that interfering with molting process can be used in an IPM approach.

Materials Needed

  • Plastic garbage bags (2-3 sizes)
  • Scissors
  • Masking tape

Timeline: 20 minutes

Procedure

  1. Take a large and medium sized plastic bag and cut along the backside most of the way up.
  2. Resecure the "seam" lightly with a few pieces of masking tape.
  3. Put plastic bags inside one another (large inside small).
  4. Get 2 volunteers. One gets inside both bags and hunkers down.
  5. Kid inside bags holds top of large inner bag up around neck. Assistant holds top of outer, smaller bag up around neckline.
  6. Instruct insect to take in air, swell and crack weakened suture of small bag in order to expand into larger bag.

Data collection

None

Analysis

None

Discussion

Topics for discussion include the significance of molting to the insect and comparison with growth in organisms that do not molt. This is a dangerous time for insects - what might happen to them?

Relevance to IPM

Molting in insects is controlled by hormones. Can you think of how we use this fact to disrupt insects' life cycles? Also, the cuticle protects insects from dehydration. Can we use this fact to our benefit?