Development and diapause

Question 1

how do insects grow with an exoskeleton

Answer 1

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

Question 2

define instar

Answer 2

each step in the insect’s development

Question 3

instar - what are immatures called

Answer 3

nymphs or larvae

Question 4

instar - what is the final instar

Answer 4

adult

Question 5

Insect development follows what general pattern

Answer 5

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

Question 6

insect development - egg

Answer 6

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

Question 7

insect development: first immature stage - In Hemimetabolous insects

Answer 7

called a nymph

Question 8

insect development: first immature stage - In Holometabolous insects

Answer 8

called a larva

Question 9

insect development - feeding and growing

Answer 9

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

Question 10

insect development - metamorphisis

Answer 10

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

Question 11

What happens during molt?

Answer 11

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

Question 12

what happens during molt? - apoysis

Answer 12

epidermis separates from cuticle

Question 13

what happens during molt? - Begin new cuticle development

Answer 13

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

Question 14

what happens during molt? - Continue new cuticle development

Answer 14

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

Question 15

what happens during molt? - Ecdysis

Answer 15

cast off old cuticle

Question 16

what happens during molt? - Expansion

Answer 16

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

Question 17

Hemimetabolous development

Answer 17

• Stingbug (Hemiptera)
• Grasshopper (Orthoptera)
• Dragonfly (Odonata)

Question 18

Hemimetabolous development - stingbug (Hemiptera)

Answer 18

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

Question 19

Hemimetabolous development - gasshopper (orthoptera)

Answer 19

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

Question 20

Hemimetabolous development - dragonfly (odonata)

Answer 20

• 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

Question 21

explain insect state after molting (ecdysis)

Answer 21

• 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

Question 22

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

Answer 22

‘callow’ or ‘teneral’ adult

Question 23

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

Answer 23

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

Question 24

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

Answer 24

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

Question 25

Holometabolous development (aka ‘complete metamorphosis’) - larva

Answer 25

Larvae very distinct from adults

Question 26

Holometabolous development (aka ‘complete metamorphosis’) - pupa

Answer 26

- ‘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

Question 27

Different types of larvae

Answer 27

- Larval forms can be diverse - Some may have > 6 legs (=prolegs) or no legs at all

Question 28

Hormonal control of molt

Answer 28

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

Question 29

hormone control of molt - Juvenile hormone (JH)

Answer 29

- high titers maintain larval molts - secreted by corpora allata (neurosensory organ) when stimulated by neuropeptides from the brain

Question 30

hormone control of molt - PTTH (Prothoracicotrophic hormone)

Answer 30

secreted by the brain, stimulates prothoracic gland to produce ecdysone

Question 31

hormone control of molt - ecdysone ('ecdyteroid')

Answer 31

stimulates production of new cuticle, molt

Question 32

explain the hormone levels that control molt

Answer 32

- 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

Question 33

Some variations on development

Answer 33

- Diapause - Genetic polymorphism - Environmental polyphenism

Question 34

variations on development - diapause

Answer 34

- 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

Question 35

variations on development: diapause - what breaks diapause?

Answer 35

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

Question 36

variations on development - Genetic polymorphism and mimicry

Answer 36

- forms depends on genotype - genetic polymorphism (Mendelian alleles) maintains discrete forms of mimic

Question 37

variations on development - environmental polyphenism

Answer 37

- forms depends on environmental influences (developmental plasticity) - aphids are an example

Question 38

variations on development: environmental polyphenism - aphid example

Answer 38

Alternate between winged/wingless sexual/asexual forms

Question 39

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

Answer 39

- 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