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Insect Bio > Development and diapause > Flashcards

Development and diapause Flashcards

1
Q

how do insects grow with an exoskeleton

A
  • Have to break out of old exoskeleton and make new, larger one (called molting)
  • Means their growth is stepwise, not continuous
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2
Q

define instar

A

each step in the insect’s development

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3
Q

instar - what are immatures called

A

nymphs or larvae

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4
Q

instar - what is the final instar

A

adult

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5
Q

Insect development follows what general pattern

A
  1. egg
  2. first immature stage
  3. feeding and growing
  4. metamorphosis
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6
Q

insect development - egg

A

embryo develops in the egg, which hatches into the next development stage

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7
Q

insect development: first immature stage - In Hemimetabolous insects

A

called a nymph

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8
Q

insect development: first immature stage - In Holometabolous insects

A

called a larva

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9
Q

insect development - feeding and growing

A

The first instar nymph/larva feeds and grows, molting into successively larger insects, until the next development stage

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10
Q

insect development - metamorphisis

A
  • the final molt into the adult (sometimes called imago) form
  • focused on mating and reproduction (also dispersal)
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11
Q

What happens during molt?

A
  1. Apoysis
  2. Begin new cuticle development
  3. Continue new cuticle development
  4. Ecdysis
  5. Expansion
  6. Complete development of new cuticle
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12
Q

what happens during molt? - apoysis

A

epidermis separates from cuticle

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13
Q

what happens during molt? - Begin new cuticle development

A
  • Begin new cuticle development under the existing old cuticle
  • excrete molting gel
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14
Q

what happens during molt? - Continue new cuticle development

A

activate enzyme in molting fluid to digest (and recycle some of) old cuticle

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15
Q

what happens during molt? - Ecdysis

A

cast off old cuticle

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16
Q

what happens during molt? - Expansion

A

expand body to fill new cuticle (swallow air or water)

17
Q

Hemimetabolous development

A
  • Stingbug (Hemiptera)
  • Grasshopper (Orthoptera)
  • Dragonfly (Odonata)
18
Q

Hemimetabolous development - stingbug (Hemiptera)

A

nymphal instars are more or less similar, but adults have wings (and genitals)

19
Q

Hemimetabolous development - gasshopper (orthoptera)

A
  • nymphal instars are more or less similar, but adults have wings (and genitals)
  • partial development of wings in 4th and 5th instars
20
Q

Hemimetabolous development - dragonfly (odonata)

A
  • While nymphs still similar from instar, adult form can be very different, especially in groups with aquatic nymphs and winged adults
  • old last nymphal instar exoskeleton: nymph climbs out of water before metamorphosis
21
Q

explain insect state after molting (ecdysis)

A
  • Insect is vulnerable (soft and immobile) for several hours after molt until new cuticle hardens
  • Especially so after imaginal (adult) molt, as wings are very delicate
22
Q

insect state after molting (ecdysis) - what is the soft form called

A

‘callow’ or ‘teneral’ adult

23
Q

insect state after molting (ecdysis) - what does the new adult often do?

A

New adult often swallows air to ‘inflate’ new cuticle; often hangs down to assist with wing emergence

24
Q

Holometabolous development (aka ‘complete metamorphosis’) - life stages

A
  1. Egg
  2. Larva
  3. Pupa (this is distinct from Hemimetabolous insects)
  4. Adult (or imago)
25
Q

Holometabolous development (aka ‘complete metamorphosis’) - larva

A

Larvae very distinct from adults

26
Q

Holometabolous development (aka ‘complete metamorphosis’) - pupa

A
  • ‘resting stage’
  • no growth, but massive physiological reorganization for larva-adult transition
  • Often involves silk or other cocoon
  • Whiter during earlier stages, when its about to emerge, more color is present
27
Q

Different types of larvae

A
  • Larval forms can be diverse
  • Some may have > 6 legs (=prolegs) or no legs at all
28
Q

Hormonal control of molt

A
  1. Juvenile hormone (JH)
  2. PTTH (Prothoracicotrophic Hormone)
  3. Ecdysone (or ‘ecdydteroid’)
29
Q

hormone control of molt - Juvenile hormone (JH)

A
  • high titers maintain larval molts
  • secreted by corpora allata (neurosensory organ) when stimulated by neuropeptides from the brain
30
Q

hormone control of molt - PTTH (Prothoracicotrophic hormone)

A

secreted by the brain, stimulates prothoracic gland to produce ecdysone

31
Q

hormone control of molt - ecdysone (‘ecdyteroid’)

A

stimulates production of new cuticle, molt

32
Q

explain the hormone levels that control molt

A
  • If ecdysone is high -> molt
  • If JH is high -> molt is larva-larva
  • If JH is low -> molt is larva-pupa
  • If JH is absent -> molt is pupa-adult
33
Q

Some variations on development

A
  • Diapause
  • Genetic polymorphism
  • Environmental polyphenism
34
Q

variations on development - diapause

A
  • Arrested development to get through unfavorable period
  • Usually overwintering, or waiting out dry period
  • Often egg or pupa (no growth), but all stages diapause in at least some species
35
Q

variations on development: diapause - what breaks diapause?

A

usually photoperiod, temperature, moisture, or a combination of them

36
Q

variations on development - Genetic polymorphism and mimicry

A
  • forms depends on genotype
  • genetic polymorphism (Mendelian alleles) maintains discrete forms of mimic
37
Q

variations on development - environmental polyphenism

A
  • forms depends on environmental influences (developmental plasticity)
  • aphids are an example
38
Q

variations on development: environmental polyphenism - aphid example

A

Alternate between winged/wingless sexual/asexual forms

39
Q

variations on development: environmental polyphenism - why can aphids alternate?

A
  • Asexual reproduction and wingless morphology lets aphids exploit resource bonanza on host and channel resources to reproduction (not mating, flight)
  • but the ability to product winged forms, mate in autumn preserves benefit of dispersal and sexual reproduction

Insect Bio (26 decks)

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