development and metamorphosis

metamorphosis definition

insects develop through a process in which they change in form (small or large)

stages of metamorphosis

1st stage - egg

2nd stage - immature

instar

3rd stage - pupa

metamorphosis - 1st stage

egg stage

can be laid individually (solitary) or in a cluster (egg mass)

metamorphosis - 2nd stage

immature

not fully grown or developed

also called a nymph or larva

nymph definition

identical to adult without wings

used to describe insects that undergo incomplete or gradual metamorphosis

larvae definition

completely different from adult

used to describe insects that undergo complete metamorphosis

instar

used to describe an insect between successive molts

usually undergo multiple molts - multiple instars

metamorphosis - 3rd stage

pupa

only for insects that undergo complete metamorphosis

larval body is broken down and adult body is developed

most are sessile or have very limited movements

molting def

the process of shedding and outer layer followed by the formation of its replacement mo

molt characteristics

most insects will stop eating during the process to conserve egy

most insects do not molt again after reaching the adult stage

cuticle characteristics

large reason for insect survival

has the ability to heal over small cuts and scrapes in larvae

responsible for muscle attachment within the insect body

formed by many layers

process of cuticle healing larvae cuts

the bottom layer of the integument will close by producing new epidermal cells → once molted the scrape will be completely replaced and gone

integument def

the entire cuticle and epidermal layers of cells

plays essential role in fighting bacterial and viral infections

layers of the cuticle

base - epidermal cells

above the epidermis is the procuticle made of the exocuticle and endocuticle

top layer is the epicuticle

procuticle characteristics

where chitin is located

endocuticle remains flexible and unrigid

chitin in the procuticle

chitin will combine with proteins to from extremely rigid structures

as more chitin and proteins bind it leads to sclerotization

forms the exocuticle

sclerotization

the appearance of a darker pigment from chitin and proteins binding

endocuticle

anywhere on the insect body needs to move and their is a lack of exocuticle

4 layers of the epicuticle

inner epicuticle

outer epicuticle

wax layer

cement layer w

wax layer of the epicuticle

was canals being in the epidermis and extend through procuticle and deposit waxes into the wax layer

cement layer in the epicuticle

made of thin lacquer like cement coating that protects the insect

molting process characteristics

takes many step but has two main components - apolysis and ecdysis

most insect have a set number of molts but some molt continuously throughout their life

apolysis

the separation of the new and old cuticle

ecdysis

the loss of the old cuticle

step 1 of the molting process

epidermis cells “let go”/detach from the old cuticle

epidermal cells divide and grow in size

• the cells start to have a wrinkled appearance to increase surface area and once insect has finished molt the cuticle can take up more space for insect growth

step 2 of the molting process

molting fluid begins to fill the space between the old cuticle and epidermis

as epidermis cells divide the epidermis (specifically outer epicuticle first) so that once the procuticle is created it has protection

once the epicuticle is complete the molting fluid enzymes are activated

molting fluid

contains enzymes that break down proteins and chitin

the enzymes are inactive up until step 2 of the molting process

step 3 of the molting process

activated enzymes begin to dissolve and breakdown the unsclerotized endocuticle and leave the sclerotized cuticle intact

• breakdown leaves a few thin hardened layers of the old cuticle to be released at a later stage

all dissolved materials are reabsorbed by the insect

step 4 of the molting process

epidermal cells continue to divide into more and from the new procuticle layers

this step can sometimes take a very long time and can continue until the old cuticle is completely shed

step 5 of the molting process

once the procuticle is fully formed or almost complete the process of ecdysis begins

• initiated by muscular and hemolymph pressure cues from inside the body

small crack will begin to form along the dorsal midline and head so the insect can later exit

if this step is disrupted the insect will likely die

exuvia

the term for the old cuticle once the insect has completely exited

step 6 of the molting process

after the insect has completely shed its old shell it must start expanding its body parts to the fullest extent before sclerotization can take place

if prematurely hardened then then there will be deformities that will likely lead to death

expands by pushing hemolymph

step 7 of molting

soon after the dermal glands down in the epidermal layers send waxes and cement through wax tubes to form the wax and cement layers of the epicuticle

metamorphosis types

ametabolous

paurometabolous

hemimetabolous

holometabolous

ametabolous

no metamorphosis

only change in size and development of functional genitalia a

molting continues into adulthood

nymphs resemble adults and adults dont have wings

ex: springtails, firebrats and silverfish

purometabolous

simple or incomplete

“gradual metamorphosis”

change in size, body proportion, development, of structures

usually have a fixed number of molts

ex: cockroaches, grasshopper, termite, mantis, true bugs

paurometabolous wing formation

early instars have no wings

late instars develop wing buds

final instar forms wings inside the buds and expend after the final molt

hemimetabolous

simple or incomplete

immatures are aquatic and adults are terrestrial

number of molts depends on species

adults have functional wings

ex: dragonfly, damselfly, mayfly, and stonefly

holometabolous

complete metamorphosis

change in form from immature or adult

no external wing development in immatures

pupal stage for breaking down immature structures and forming adults

wings develop internally in pupa and expand once adult emerges

ex: beetles, flies, bees, butterlfies

larval forms

campodeiform

scarabaeiform

eruciform

elateriform

carabiform

vermiform

platyform

campodeiform larva

flattened body

filaments at the end of the abdomen

long legs

usually predators

ex: aquatic beetles, lacewings, and caddisflies

scarabeiform

c shaped

well developed head

short thoracic legs

burrow in soil

ex: scarab beetles, weevil, and furniture beetles

eruciform

cylindrical

most have a well developed head

remain close to or on their food source

ex: butterflies, moths, scorpions and sawflies

elateriform

cylindrical

smooth

tough skin

short legs

ex: click beetle and darkling beetles

carabiform

similar to the campodeiform except shorter legs and no filaments

ex: ground and leaf beetles

vermiform

cylindrical

no legs

elongated

the form of maggots, honey bees, and wood boring beetles

platyform

broad flat body

short or absent legs

not a common form

ex: syrphid, flies, certain caterpillars and blister beetles

pupal forms

obtect

exarate

coarcate ob

obtect pupal

appendages are tightly associated to the body and completely enclosed

ex: butterflies and moths

exarate pupal

appendages are free from the body

ex: wasps, bees and some beetles

carcate pupa

appendages are NOT visible

pupa is enclose in puparium

ex: fliespupari

puparium def

pupa formed from the exuviate of the last instar stage