Metamorphosis (Lab Exam 2)

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Metamorphosis

Back 1

a series of postembryonic stages before reaching the mature adult or imago stage

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Molting

Back 2

exoskeleton is periodically shed and replaced by a slightly larger one

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Exuvium

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the old "skin" from molting

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Instar

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Each molting stage until adult stage

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First Instar

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- immature insect immediately following eclosion

- feed and grow to point where a molt would become necessary

- typical duration of 3 days (varied)

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Second Instar

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molt after first instar

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Stadium

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represents factor of time that is the duration of each stage

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Apolysis

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process whereby the old cuticle separates from the newly formed exoskeleton

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Ecdysis

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actual event whereby the insect pulls itself out of the old cuticle and "sheds its skin"

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Ecdysial lines (ecdysial sutures)

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specific weakened areas where the old exoskeleton generally splits

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Pharate

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- time between apolysis and ecdysis

- may last from a matter of moments to extended periods of time

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Teneral

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- insect resembles an "albino"

- new cuticle is soft, flexible and light colored

- insects will gulp air/water to expand cuticle before it hardens

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Incomplete Metamorphosis

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- immature stage (nymphs) grossly resembles adult except for absence of wings and smaller size

- wing development is external, starting with small wing buds or wing pads

- immatures typically occupy the same general habitat as adults and feed similarly

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Complete Metamorphosis

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- immature stages(larvae, pupa) usually very different from adult in general appearance

- wing development internal, from dormant masses of cells, the wing Anlagen

- immatures frequently occupy a much different habitat than the adult; feeding strategy may be very different

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Larvae

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the active feeding immature stage

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Pupae

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transitional form characterized by nearly complete internal and external re-arrangement of organs and structural features

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Ametabolous Development (Ametamorphosis)

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- applies to groups which continue to molt throughout adult life

- primitively wingless

- immatures= immatures or nymphs

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Paurometabolous Development

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- "gradual" metamorphosis

- immatures= nymphs

- adults have wings, but some sedentary plant feeders and animal parasites lost secondary wings

- nymphs & adults have same environment and feeding habits (= same type of mouthparts)

- wings develop as external wing pads, only functional in adults

- five distinct nymphal instars

- all members of Polyneoptera and Paraneoptera, except Plecoptera

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Hemimetabolous Development

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- special type of gradual metamorphosis

- immatures= naiads (aquatic)

- wing development similar to paurometabolous

- development often prolonged over year or several

- not unusual to find 15+ instars

- paleopterus orders: Odonata, Ephemeroptera (mayflies) and Plecoptera (stoneflies)

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Holometabolous Development

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- postembryonic development/ complete metamorphosis

- pupa may be housed in protective cocoon of silk or other, or hardened exuvium

- orders making up the Division Endopterygota

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Puparium

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entire entity of pupa housed/formed within hardened exuvium of preceding larval instar

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Larval Forms

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- Eruciform (catepillar)

- Scarabaeiform (grub-like)

- Campodeiform

- Elateriform (wireworms...)

- Cerambycoid

- Vermiform (maggots...)

- Obtect

- Exarate: decticous (=mandibles functional) and adecticous (=lack functional mandibles)

- Coarctate