補充教材2

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Reproduction and development

Yong-Chao Su

KMU

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Reproductive organs of insects

• Similar to vertebrates: male>sperm; female

->eggs.

• _{Most insect species reproduce sexually}

• _{There are also many species (eusocial bees)}

that reproduce by parthenogenesis, asexual

reproduction in which there is growth and

development of an unfertilized egg.

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Prior mating

(before mating)

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Nuptial gift giving

behavior of Mecoptera

(長翅目)

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Nuptial gift giving behavior of Anabrus

Protein, no sperm Sperm

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Mating

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Copulation

Female

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Do all insects copulate?

• NO.

• Wingless orders Archeognatha and Thysanura

used indirect sperm transfer

• _{The thing they use is spermatophores to transfer}

sperm

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Species specific male genitalia

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Species specific female genitalia

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Other characters to avoid matting with wrong species

(so are good character for diagnose species)

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Post-mating

(after mating)

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Post Oviposition– Maternal care

(parasitoid)

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Atypical modes of reproduction

• “Normal” reproduction: gonochorism,

amphimixis, diploidy.

• _{Atypical reproduction:}

• Parthenogenesis (孤雌生殖) - Aphids

• Paedoyenesis (幼體生殖)- Diptera

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Development

Egg to bug

(Eggz2Bugz?)

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The insect egg

Oocyte

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The insect egg

Vitelline membrane Oocyte

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The insect egg

Chorion Oocyte

1st _{metaphase nucleus}

Vitelline membrane

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The insect egg

Vitelline membrane Chorion Oocyte 1st _{metaphase nucleus} Micropyle Aeropyles

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The insect egg

Vitelline membrane

Chorion Oocyte

1st _{metaphase nucleus}

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The insect egg

Vitelline membrane Chorion Oocyte 1st _{metaphase nucleus} Micropyle

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The insect egg

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The insect egg

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The insect egg

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The insect egg

Vitelline membrane Chorion Oocyte 1st _{metaphase nucleus} Micropyle Cross section

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The insect egg

Vitelline membrane Chorion Oocyte 1st _{metaphase nucleus} Micropyle From outside

Chorion peeled off

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Germ Band-side view

Yolk with blastoderm Membrane covering

Head end Tail end

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Germ Band side view

Ventrally, cells thicken, form germ anlage (undeveloped cell layers)

Head end Tail end

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Germ Band ventral view

Head end Tail end

Groove forms—

now blue structure is the germ band; Will form 2 layers of tissues

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Germ Band side view again

Head end Tail end

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Now, cross section

Tail end

yolk

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Embryo side view

Head end Tail end

Inner mesoderm layer, outer ectoderm layer

Hindgut Foregut

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Embryo side view

Head end Tail end

Hindgut Foregut

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Embryo side view

Head end Tail end

Hindgut Foregut

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Embryo side view

Head end Tail end

Endoderm layer forms midgut

Hindgut Foregut

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Embryo side view

Head end Tail end

Endoderm layer forms midgut

Hindgut Foregut

Blob of yolk

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As the embryo grows..

• Limb buds develop into limb-derived

structures.

• _{Gut is completed}

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The young insect

• _{Hemimetabolous}

• _{“half” transformation}

• _{Immatures called}

nymphs

• _{Nymphs resemble}

adults except for wings,

genitalia

• _{Holometabolous}

• _{“whole” transformation}

• _{Immatures called larvae}

• _{Larvae completely}

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Asian

long-horned beetle

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Ametabolous insects

• Essentially no external changes from

immature to adult

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Growing means molting

• New, larger cuticle forms under theold cuticle

• Cuticle is shed

• _{New larger cuticle expands, is sclerotized}

• (There’s MUCH MORE to this!)

• Number of molts to adult varies.

• _{MOST insects do not as adults}

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Growing means molting

• Instars and molts: hemimetabolous

Eclosion

₁

st

_molt

2

nd

molt

3

rd

molt

1

st

_instar

nymph

2

nd

_instar

nymph

3

rd

_instar

nymph

4

th

_instar

nymph

Imago or Adult

(56)

Growing means molting

• Instars and molts: holometabolous

Eclosion

₁

st

_molt

2

nd

molt

3

rd

molt

Imago or Adult

1

st

_instar

larva

2

nd

_instar

larva

3

rd

_instar

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Development

• _{Types of metamorphosis:}

• _{Ametaboly – no change}

• Himemetaboly – some changes

• _{Holometaoly – changed all}

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Integument is complex

• Composed of many layers

• _{Living cells}

• _{Secreted layers}

• _{Perforated by pores}

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Three basic components

Basement membrane Epidermis: living cells

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Three basic components

Secreted by blood cells and others.. Epidermis (living cells)

Secreted mainly

by epidermis; contains CHITIN

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Fine structure of cuticle

Epicuticle: proteins & lipids

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Epicuticle: 1- 4 micrometers

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Chitin fibers secreted in layers

• _{Chitin fibers embedded in protein matrix}

• _{Orientation of chitin fibers changes}

• _{Like plywood: layers oriented in different}

directions increases strength

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Epicuticle

Procuticle

Exocuticle

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Tanning or sclerotization

• _{In exocuticle}

• _{Protein-protein cross linkages}

• More cross-linkage, exocuticle is stiffer,

more rigid

• _{Thin flexible membrane at joints not}

sclerotized

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Epicuticle: thin, but crucial

• _{1-4 micrometers}

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Epicuticle

Procuticle

Exocuticle

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Layers of epicuticle

Etc. 0.5-2.0 μm 0.015 μm inner outer wax cement

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Layers of epicuticle

• _{Secreted by epidermis}

• Remember the epidermis?

• _{Living cells}

• _{Cement layer: mucopolysaccharide}

• Protects

• _{Wax: hydrocarbons}

• Waterproofs

• _{Distinctive odors}

• Blooms, fluffs

• _{Outer layer: polymerized lipids}

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Molting

• https://www.youtube.com/watch?v=QfeEZl0V

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Summary of Molting

Step 1: Apolysis -- separation of old exoskeleton from epidermis

Step 2: Secretion of inactive molting fluid by epidermis

Step 3: Production of cuticulin layer for new exoskeleton

Step 4: Activation of molting fluid

Step 5: Digestion and absorption of old endocuticle

Step 6: Epidermis secretes new procuticle

Step 7: Ecdysis -- shedding the old exo- and epicuticle

Step 8: Expansion of new integument