9. Growth and Metamorphosis

hy can't insects grow continuously?

Their rigid cuticle (exoskeleton) prevents continuous expansion.

How do insects grow?

By moulting (ecdysis).

What is metamorphosis?

The change in form that occurs after an insect hatches from the egg.

hy is understanding metamorphosis important in pest management?

Different life stages behave differently and may require different control methods.

What is moulting (ecdysis)?

Shedding the old cuticle so the insect can grow.

Why must insects moult?

Their exoskeleton cannot stretch.

What is an instar?

The stage between two moults.

How many instars can an insect have?

 It varies depending on the species.

What is the immature stage?

The growth phase before adulthood.

How long can the immature stage last?

Days, weeks or even years depending on the species.

What is the main purpose of the adult stage?

 Finding mates, reproducing and dispersing.

What is dormancy (quiescence)?

 A temporary pause in activity caused by unfavourable environmental conditions

 What causes quiescence?

Conditions such as cold temperatures, lack of food or low moisture.

What is diapause?

 A programmed dormancy controlled by hormones and environmental cues.

 What commonly triggers diapause?

• Season

• Day length

• Hormonal changes

What is the difference between quiescence and diapause?

 Quiescence is an immediate response to poor conditions, while diapause is a programmed, hormone-controlled dormancy.

Name six factors that affect insect growth rate.

• Temperature

• Food quality

• Food quantity

• Moisture and humidity

• Species biology

• Environmental conditions

• Life stage

How does warm temperature affect insect growth?

It usually speeds up development.

 How does cold temperature affect insect growth?

It slows development.

How does poor food affect insect growth?

It slows development and may reduce survival.

 How does unsuitable moisture affect insects?

It slows development or increases dormancy.

What is primitive metamorphosis also called?

Ametabolous metamorphosis.

What is the life cycle of primitive metamorphosis?

Egg → Young → Adult.

How do young insects compare to adults in primitive metamorphosis?

They look very similar.

Do primitive adults continue moulting?

Yes, many do.

Give an example of an insect with primitive metamorphosis.

Silverfish.

Why are primitive insects usually easier to control?

 Young and adults live in similar places and eat similar food.

What are the other names for incomplete metamorphosis?

Hemimetabolous or gradual metamorphosis.

What is the life cycle of incomplete metamorphosis?

Egg → Nymph → Adult.

What is the immature stage called?

Nymph.

How do nymphs compare to adults?

 They resemble adults but lack wings and reproductive organs.

Is there a pupal stage in incomplete metamorphosis?

No.

Name six insects with incomplete metamorphosis.

• Cockroaches

• Termites

• Bed bugs

• Lice

• Earwigs

• Grasshoppers

• Psocids

Why are incomplete metamorphosis insects usually treated similarly at all life stages?

Adults and nymphs live in similar harbourages and have similar feeding habits.

What is complete metamorphosis also called?

Holometabolous metamorphosis.

What is the life cycle of complete metamorphosis?

Egg → Larva → Pupa → Adult.

Which life stage of complete metamorphosis mainly eats and grows?

Larva.

complete metamorphosis: Which life stage transforms into the adult?

Pupa.

Which life stage mainly reproduces and disperses?

Adult.

Name six insects with complete metamorphosis.

• Flies

• Fleas

• Beetles

• Moths

• Ants

• Bees

• Wasps

Why is complete metamorphosis more difficult to control?

Different life stages live in different places and require different treatments.

Why does complete metamorphosis reduce competition?

 Larvae and adults usually eat different foods and occupy different habitats.

Why does complete metamorphosis make pest control more difficult?

Every life stage may require a different treatment strategy.

Which flea stage bites people?

Adults.

Where do flea larvae develop?

Carpets, bedding and floor cracks.

Why isn't killing adult fleas enough?

Larvae and pupae remain in the environment.

Where do fly maggots develop?

Wet decaying organic matter.

Why is source reduction important for fly control?

 Removing breeding material stops new flies from developing.

Which moth stage usually damages food and fabrics?

Larvae (caterpillars).

Do adult moths usually cause the damage?

No.

Which cockroach stages use the same harbourages?

Nymphs and adults.

Why are crack-and-crevice treatments effective for cockroaches?

Both adults and nymphs hide in the same places.

Why is identifying the life stage important before treatment?

Different life stages require different management strategies.

Why can an insecticide appear to fail even if it kills adults?

 Eggs, larvae or pupae may survive and produce new adults later.

Why are flea infestations difficult to eliminate?

Several life stages are hidden in the environment.

Why do cockroach treatments often require follow-up visits?

Eggs may hatch after the initial treatment.

Which type of metamorphosis has no pupal stage?

Primitive metamorphosis

Incomplete (gradual) metamorphosis.

Which type of metamorphosis has a pupal stage?

Complete metamorphosis.

Which type of metamorphosis allows adults to continue moulting?

Primitive (ametabolous) metamorphosis.

Primitive life cycle?

Egg → Young → Adult.

Incomplete life cycle?

Egg → Nymph → Adult.

Complete life cycle?

Egg → Larva → Pupa → Adult.

Which metamorphosis has nymphs?

Incomplete.

Which metamorphosis has larvae?

Complete.

Which metamorphosis has pupae?

Complete.

Which metamorphosis has young that resemble adults?

 Primitive.

What is moulting?

 Shedding the old cuticle.

What is an instar?

The stage between moults.

What is diapause?

Programmed dormancy.

Warm temperatures generally do what?

Speed insect development.

Poor food generally does what?

Slows insect development.

 Match each metamorphosis type to its life cycle.

• Primitive (ametabolous)

• Incomplete (hemimetabolous)

• Complete (holometabolous)

• Primitive (ametabolous) → Egg → Young → Adult

• Incomplete (hemimetabolous) → Egg → Nymph → Adult

• Complete (holometabolous) → Egg → Larva → Pupa → Adult

Match each insect to its metamorphosis type.

• Silverfish →

• Cockroaches →

• Termites →

• Bed bugs →

• Flies →

• Fleas →

• Beetles →

• Moths →

• Ants →

• Bees →

• Wasps →

• Silverfish → Primitive

• Cockroaches → Incomplete

• Termites → Incomplete

• Bed bugs → Incomplete

• Flies → Complete

• Fleas → Complete

• Beetles → Complete

• Moths → Complete

• Ants → Complete

• Bees → Complete

• Wasps → Complete

What is the single most important question to ask before choosing a treatment?

Which life stage is causing the problem, and where are the other life stages hiding?