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9.20: Insect Reproduction and Life Cycle

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These butterfly eggs look like tiny pearls on a leaf. The adult butterfly often lays her eggs on a specific type of plant. This ensures that the future caterpillars will have plenty of food to eat.

Insect Reproduction and Life Cycle

Most insects can reproduce very quickly within a short period of time. With a short generation time, they evolve faster and can quickly adjust to environmental changes. Most insects reproduce by sexual reproduction . The female produces eggs, which are fertilized by the male, and then the eggs are usually placed near the required food. In some insects, there is asexual reproduction during which the offspring come from a single parent. In this type of reproduction, the offspring are almost identical to the mother. This is most often seen in aphids and scale insects.

With a few exceptions, all insect life begins as an egg. After leaving the egg, insects must grow and transform until reaching adulthood. Only the adult insect can mate and reproduce. The physical transformation of an insect from one stage of its life cycle to another is known as metamorphosis .

Three Types of Metamorphosis

An insect can have one of three types of metamorphosis and life cycles ( Table below ). Metamorphosis describes how insects transform from an immature or young insect into an adult insect in at least two stages. Insects may undergo gradual metamorphosis (incomplete), where transformation is subtle, or complete metamorphosis, where each stage of the life cycle appears quite different from the others. In some insects, there may be no true metamorphosis at all.

Type of Metamorphosis Characteristics Examples
None
  • Only difference between adult and larvae (young or non-adult insects) is size.
  • Occurs in the most primitive insects.
  • Newborn insect looks like a tiny version of the adult.
Silverfish, firebrats, springtails
Incomplete
  • Three stages: egg, nymph, and adult.
  • Young, called nymphs , usually similar to adult.
  • Growth occurs during the nymph stage.
  • Wings then appear as buds on nymphs or early forms.
  • When last molt is completed, wings expand to full adult size.
Dragonflies, grasshoppers, mantids, cockroaches, termites
Complete
  • Most insects undergo this type.
  • Each stage of the life cycle—egg, larva, pupa, and adult—looks different from the others.
  • Immature and adult stages have different forms, have different behaviors, and live in different habitats.
  • Immature form is called larvae and remains similar in form but increases in size.
  • Larvae usually have chewing mouthparts even if adult mouthparts are sucking ones.
  • At last larval stage of development, insect forms into pupa ( Figure below ) and does not eat or move.
  • During pupa stage, wing development begins, after which the adult emerges.
Butterflies, moths, flies, ants, bees, beetles

The chrysalis (pupal stage) of a monarch butterfly

The chrysalis (pupal stage) of a monarch butterfly.

Vocabulary

  • asexual reproduction : Offspring come from a single parent.
  • larvae : Immature form of an insect.
  • metamorphosis : Process of transformation from an immature form into an adult.
  • nymph : Immature form of some insects that somewhat resembles the adult.
  • pupa : Non-feeding stage between the immature form and adult in the metamorphosis of some insects.
  • sexual reproduction : Offspring come from combining the genetic material of two parents.

Summary

  • Insects reproduce rapidly, usually by sexual reproduction.
  • Metamorphosis, or how insects transform from an immature form into an adult, can be part of the insect life cycle.

Explore More

Use the resources below to answer the questions that follow.

Explore More I

  1. How many eggs will a female monarch butterfly lay?
  2. How much heavier is the caterpillar two weeks after birth?
  3. Describe the changes that turn the caterpillar into a butterfly.

Explore More II

  1. How do male insects try to keep other males from impregnating a female with which they have mated?
  2. Do most insects use internal or external fertilization?
  3. What do male insects make with the accessory glands of their reproductive system?

Review

  1. Describe how most insects reproduce.
  2. Define metamorphosis.
  3. What is the difference between complete and incomplete metamorphosis.
  4. What are the four stages of complete metamorphosis?
  5. Describe the differences between the immature and adult forms of most insects.
  6. Give three examples of insects that go through complete metamorphosis.

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Difficulty Level:

At Grade

Grades:

7 , 8

Date Created:

Nov 29, 2012

Last Modified:

Aug 28, 2014
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