Lecture 6 - growth and metamorphosis

molting

synthesis of new cuticle

ecdysis

shedding of old cuticle

what is molting and ecdysis dependent on

environmental conditions such as temperature and humidity

what is molting and ecdysis controlled by

hormones (juvenile hormone, ecdysone)

instar

stage between molts

What happens when molting/ecdysis?

apolysis starts the seperation of old and new skeleton under endocuticle, digestion of old endocuticle, shedding, expansion of new exocuticle and epicuticle, and sclerotization(hardening) of new exocuticle

what is ecdysis triggered by

a molting hormone

juvenile hormone

produced when young

layers of insect skin (inside to outside)

epidermis, endocuticle, exocuticle, epicuticle

exuviae

old shed skin

teneral

newly molted insect

What happens just before sclerotization and right after ecdysis?

Insect enlarges to its new size by taking in air or water and expands its wings by forcing hemolymph into their veins.

sclerotization

cross-linkage of proteins, reduction in exoskeleton water content, exoskeleton hardens, colors darken.

can insects regrow parts?

Yes, depending on where the damage is and what life stage its in.

explain the process of molting/ecdysis

An insects exoskeleton does not grow as they grow, so the molting process is vital for the insect to increase in size. the endocuticle separates from the epidermis and is recycled. then a new cuticle is formed. the insect then goes through ecdysis. the old exo and epicuticle are shed, and this shed skin is called exuviae. then the teneral insect enters an intar stage, and the new exoskeleton sclerotizes.

what is metamorphosis?

change in form during life of insect

metamorphosis growth categorized into 3 patterns:

ametabolous, hemimetabolous, holometabolous

2 phase process of metamorphosis:

histolysis, histogenesis

histolysis

larval structures are broken down, material is recycled

histogenesis

develops adult structures from broken down larval structures

Ametabolous life cycle

egg to young to adult. no major changes, only obvious difference is size. (silverfish, springtails)

hemimetabolous life cycle

egg to nymph/naiad to adult. no pupal stage. wing development. orthoptera, hemiptera, mantodea, odonata, dermaptera, blattodea

nymphs:

part of hemimetabolous life cycle. live in same habitat as adults. true bugs, grasshoppers, mantids, cockroaches

naiads:

part of hemimetabolous life cycle. live in different habitat as adults. dragonflies, mayflies

holometabolous life cycle

egg to larva to pupa to adult. complete metamorphosis. butterflies, beetles, bees, wasps, ants, flies

lepidoptera larva is called

caterpillars

coleoptera larva is called

grubs

diptera larva is called

maggots

early understanding of metamorphosis

completely different organisms, spontaneous generation, accidental mating

ecdysone

hormone that promotes molting