6. Growth, Moulting and metamorphosis

What is moulting

Moulting is the process or replacing the old exoskeleton/cuticle with a new exoskeleton/cuticle so the insect can grow

Insect are not able to enlarge their hardened cuticle/exoskeleton, so an immature insect increases in size by going through moulting

What is a Instar?

Do different species have the same number of moults

Is the development stage between two successive moults.

Different species have different number of moults

What is the mouting The moulting process

• Apolysis → Old cuticle separates from the epidermis

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• New cuticle forms —> New cuticle is formed underneath the old exocuticle by the epidermis while much of the old endocuticle is digested and recycled

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• Ecdysis → Remaining old cuticle/exoskeleton splits and sheds

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• Expansion + Scelerotisation → New cuticle/exoskeleton expands allowing the insect to grow while it hardens and darkens

Insect is particularly vulnerable before new cuticle hardens

Old shed cuticle is called a Exuvia/Cast Skin

What hormones is responsible for initiating and coordination moulting process

Ecdysteroids

What is ecdysteroids responsible for

Responsible for initiating and coordinating the moulting process

What hormone influences if an insect undergoes metamorphosis during moulting

Juvenile Hormone

Why is juvenile hormone important

Juvenile hormone influences if an insect undergoes metamorphosis during moulting.

If juvenile hormone is high during moulting the insect remains immature

If juvenile hormone is low/absent during moulting then the insect undergoes metamorphosis during moulting

How do IGR’s fit into moulting

IGR’s such as juvenile hormone mimics and analogues disrupt metamorphosis by keeping juvenile hormone high during moulting preventing the insect from undergoing metamorphosis

Name the 5 things that effect insect development and growth

Temperature - Warmer conditions normally speed up growth and development

Food quality/Quantity - Adequate nutrition supports faster growth

Moisture - Adequate moisture improve survival/development

Species - Different species naturally develop at different rates

Other unsuitable environmental conditions

Name two important IGR’s

Juvenile-Hormone mimics (IRAC 7)

• Disrupt metamorphosis by keeping juvenile hormone elevated during moulting

Chitin-synthesis inhibitors (IRAC 15)

• Interfere with chitin formation of the new cuticle/exoskeleton

What may insect entre to survive unfavourable conditions or predictable seasonal changes

Dormancy

What is dormancy

Dormancy is a temporary period of reduced activity, growth and development that helps an insect survive unsuitable conditions

What are the two main types of dormancy

Quiescence - Immediate response to bad conditions

• Activity/development slows or stops because conditions are currently unsuitable and resumes as soon as they become suitable again

• example: middle of summer and an cold summer day arrives which makes them inactive. As soon as the weather warms up again they become active again

Diapause - programmed seasonal pause

• A programmed seasonal pause in activity/development caused by hormonal response initiated by seasonal cues. It does not end if conditions temporarily improve but carries on until the seasonal response ends.

• Insect enters diapause during winter when it gets cold and even if there are some hot days it remains in diapause until the season get warmer

What is metamorphosis

A change in body form during development from immature stage to adult stage

another name for

Primitive metamorphosis

Incomplete metamorphosis

Complete metamorphosis

Ametabolous

Hemimetabolous

Holometabolous

Life cycle of ametabolous

how do immature stage and adult differ

Examples

Egg → Young → Adult

Young resemble adult except they are smaller and sexually immature

Life cycle of hemimetabolous

how do immature stage and adult differ

Examples

Egg → Nymph → Adult

Nymph resemble adult except they are smaller and sexually immature. wings and reproductive structures develop progressively

Cockroaches/Termites → Bed bugs/true bugs → Lice/booklice → Earwigs → Grasshoppers/Crickets/locust→ Thrips (intermediate metamorphous )

Life cycle of holometabolous

how do immature stage and adult differ

Examples

Egg → Larva → Pupa → Adult

Larva are completely different from adults in body form and may also differ in diet, habitat and behaviour

Ants/bee/wasp → Flies/mosquitoes/midges/gnats → Fleas → Beetles → Moths/butterflies

It terms of pest control why is metamorphosis important when it comes to Hemimetabolous and holometabolous?

Hemimetabolous/incomplete metamorphosis

• Nymph have similar body form and usually similar habitats, food and behaviour as the adults

• The same treatment is often effective on both Nymph and adult because they have similar body form habitats, food and behaviour

holometabolous/complete metamorphosis

• Larva are completely different from adults in body form and may also differ in diet, habitat and behaviour and make also cause different damages or problems to humans

• Different control methods may be required

• This gives them distinct advantages because often lava and adult are not competing for food with each other and different treatments methods are needed to handle both forms