Knowledge about insect reproduction and development can be used to apply control measures at times when the pest is most susceptible.
Most insects reproduce by males fertilizing the eggs of a female. A few insects give birth to live young; however, life for most insects begins as an egg. Eggs may be deposited as a single egg or in masses. The area in which the eggs are laid may influence the time of hatching.
When an insect first hatches from an egg, it begins to feed and grows until its skin cannot stretch further. The growth stages between molts are called instars – the last growth stage is the adult. The number of instars varies with different insects and in some cases, may vary with the temperature, humidity and availability and kinds of food. Most of the feeding occurs during the final two instars.
Some insects change their shape or acquire new characteristics as they become adults. This change is called metamorphosis. There are three main types of insect development:
- No Metamorphosis
- Gradual or Incomplete Metamorphosis
- Complete Metamorphosis
No Metamorphosis
There are three stages of development.
- Egg
- young
- adult
The young (juvenile stages) visually resemble the adult stage, except they are smaller. A few insects have this type of development, (e.g. silverfish).
Gradual or Incomplete Metamorphosis
There are three development stages:
- egg
- nymph
- adult.
Nymphs are missing certain adult features (e.g. wings or reproductive organs) when they hatch, but gradually develop these features as they mature. Wings become fully developed only in the adult stage. An insect having gradual or incomplete Metamorphosis is the cockroach.
Complete Metamorphosis
Four development stages are recognized:
- egg
- larva
- pupa
- adult.
Larvae hatch from the egg and grow larger by molting and passing through one to several instar stages. The larvae do not resemble the adult stage. The true or thoracic legs of larvae may be underdeveloped; some have false legs (prolegs) in the abdominal region and others have no legs at all. Other names for the larval stage of certain insects are:
- Caterpillars – the larvae of moths
- Grubs larvae of beetles
- Maggots the legless larvae of flies.
The pupa is a resting stage during which the larva radically changes shape to become an adult with legs, wings, antennae, and functional reproductive organs.