ENT 201 Lecture 7 Notes- Growth and Metamorphosis

Biotic Transformations—Growth and Metamorphosis

ANIMAL GROWTH AND DEVELOPMENT

sperm and egg fertilize egg, create embryo, hatches into newborn, immature young, adult

Insect Eggs

•Generally small

•Can vary in size, shape, color, etc.

•Deposited individually, in clumps, or masses (sometimes dirt is shoveled on top)

•May be deposited on, in, or near food (or in water) (butterflies use milkweed to feed larvae immediately)

What is science without exception?

There are exceptions to every rule of science

Chorion

the outermost membrane surrounding an embryo’s egg (an egg’s shell)

Egg Laying

Many insects have evolved unique ways to protect their eggs

* Some insects plant their eggs in another animal, like how bot flies plant eggs in humans or cows. Or the insect lays their egg on a smaller insect that doesn’t realize they’re there.

How do insects escape the egg?

Many will chew or dissolve their way out (a chemical to

Immature Insects

•Called larvae (active immature form), nymphs (have simple metamorphosis), or naiads (aquatic versions)

•Their only job is to acquire nutrients and grow

\-Molting

\-Future Reproduction

•Instars (developmental stage of arthropods)

•Pupae

Adult Insects

•The final stage in insects

•Responsible for reproduction

•Only stage with functional wings

Insect Metamorphosis

•Meta - To change

•Morphosis - Form or Shape

•The type of metamorphosis depends on the group of insect

Ametabolous Development

•Never have wings

•Goes directly from egg -> nymph -> adult

•Adults and Nymphs all live in the same environment

•A-  - without ; -metabolous - metamorphosis

Hemimetabolous Development

•Hemi-  - Half (Partial) ; -metabolous - Metamorphosis

•Also goes from egg -> nymph -> adult

•Nymphs look like adults, except in later instars

\-Live in the same environment

•Adults have wings and reproductive organs

•Subimago

Holometabolous Development

•Holo- complete ;  -metabolous – development

•Go from egg -> larva -> pupa -> adult

•Larva and adults look VERY different

•Pupal stage acts as the “resting” stage

•Adults emerge from pupa with reproductive organs and wings

Generation

•The length of a generation can vary from days to years

\-Egg à Egg = One generation

•What can impact the length of a generation?

\-Temperature

\-Humidity

\-Daylight length

Regulating Molting

•The endocrine system of insects regulates growth and molting

•This system includes hormones that act as chemical messengers

\
Molting hormone (MH) & Juvenile hormone (JH) key players

\
  MH + a lot of JH >>> larval cuticle

\
  MH + a little JH >>> pupal cuticle

\
  MH >>> adult cuticle

Temperature

•Most insects die at 140-150 for 1 hour

•125-135 F for 4-5 hours

•Most insects slow down at 40 F

•Most die at 0 F for 4-5 hours

How could we use insect/temperature information to control pest insects?

Heat treatment

Give an example of a possible pest insect

Carpet beetle

Can you explain how the Arctic wooly bear caterpillar can live at -90F comfortably?

It has antifreeze in its blood

How else does temperature affect insect growth?

1. Metabolic rate: The metabolic rate of insects is directly proportional to temperature. As the temperature increases, so does their metabolism, which can lead to faster growth and development.
2. Diapause: Some insects have a life stage known as diapause, where they stop developing and remain in a dormant state. The onset and termination of diapause can be triggered by changes in temperature, such as the arrival of winter or the onset of spring.
3. Reproduction: Temperature can also affect the reproductive capability of insects, with some species requiring specific temperatures for successful mating and egg laying.

What is poikilothermy?

Poikilothermy is a term used to describe animals that have a body temperature that varies with the external environment. These animals, also known as "cold-blooded," are unable to regulate their internal body temperature and are dependent on external heat sources to warm up and internal mechanisms to cool down.

Ectothermic

Insects that rely on their environment to regular their body temperature

Diapause

A period of suspended development

What controls diapause?

Hormones, Daylight, Temperature

Tanning

Once the remains of the exoskeleton from the previous stage have been shed during ecdysis, the new one is rapidly sclerotized (hardened) and melanized (pigmented), a process collectively known as tanning.

subimago

A stage in the development of certain insects, intermediate between pupa and imago (last stage an insect attains during its metamorphosis), during which the insect can fly but must shed a skin before becoming mature.

desiccation

the state of being extremely dry (insects can die from this)