EXAM #2

Question 1

What is insect ontogeny?

Answer 1

Developmental history from insect to adult. Includes changes in size (growth) and form.

Question 2

Why is insect growth discontinuous?

Answer 2

Because rigid cuticle limits expansion. Discontinuous growth involves molting. Non-sclerotized portions of body can grow without molting.

Question 3

Two components of growth?

Answer 3

Molt increment: Increase in size from one instar to next. Intermolt interval: instar duration (stadium).

Question 4

What is apolysis and ecdysis?

Answer 4

Apolysis: separation of old cuticle from new cuticle during molting.
Ecdysis: Casting off old cuticle (final stage of molting)

Question 5

What are the two types of insect growth? Discuss it.

Answer 5

Indeterminate: Continue to molt until death, no terminal molt. Primitive insects - collembolans, diplurans, apterygotes.
Determinate: Terminal molt. Cessation of growth and molting. All other insects.

Question 6

What are the three types of developmental morphological changes in insects?

Answer 6

Ametaboly
Hemimetaboly
Holometaboly

Question 7

Discuss the ametaboly development and give examples of insects that undergo this morphological change.

Answer 7

Primitive form that emerge from eggs. Juveniles are morphologically similar to adults (excepet for genitalia). Adults continue to molt after sexual maturity (indeterminate growth). no metamorphosis, no wings. Examples of apterygotes are silverfish and bristletails.

Question 8

Discuss the hemimetaboly development and give examples of insects that undergo this morphological change.

Answer 8

Incomplete metamorphosis. Immatures are called nymphs. Wing development. Examples are hemiptera, orthoptera, blattodea, dermaptera, etc.

Question 9

Discuss the holometaboly development and give examples of insects that undergo this morphological change.

Answer 9

Complete metamorphosis. Immatures are called larvae. Pupal stage. Wing development. Examples are Coleoptera, Hymenoptera, Deptera, and Lepidoptera.

Question 10

Special evolutionary features of holometaboly?

Answer 10

Holometaboly allows immatures and adults to specialize on different resources and to ocuppy different ecological niches.

Question 11

What are the three types of holometaboly larvae? Which caractheristics distinguish them?

Answer 11

Polypod: Cylindrical body. Shot toracic legs. Abdominal prolegs.
Oligopod: No prolegs. prognathous mouthparts.
Apod: Lack true legs. maggot-like.

Question 12

Heteromorphosis

Answer 12

In some insects, different immature stages instar may have different forms.

Question 13

Whats is diapause? how and when does it happen?

Answer 13

Its a type of development interruption triggered by environmental cues such as photoperiod, food quality, and temperature. Diapause involves adaptive physiological changes of “antifreeze” compunds in hemolymph. May be obligatory of facultative.

Question 14

What triggers brain to secrete PTTH?

Answer 14

Environmental cues;
Attaining a certain weight or size (most common);
Stretching of abdomen after blood meal;

Question 15

PTTH and ecdysteroids

Answer 15

PTTH is secreted by neurosecretory cells in the brain and relased to corpora alata or corpora cardiaca for storage and later relase into hemolymph. PTTH travels to protothoracic gland and activate synthesis of ecdysone, which is released into hemolymph and converted into 20-hydroxyecdysone, the molting hormone,

Question 16

What does 20-hydroxyecdysone do?

Answer 16

It binds to target receptors on epidermal cells and stimulates mitosis of these cellls, apolysis of old cuticle, and secretion of new cuticle.

Question 17

Role of JH in molting

Answer 17

Secreted and synthesized by corpora allata, levels of JH determine the types of molting. When JH is present, it modifies secretion of cuticle such that the next molt is of the juvenile type.

Question 18

What happens with the cuticle after 20-hydroxyecdysone activation?

Answer 18

Epidermal cells retract from old cuticle. After apolysis, the old endocuticle is digested and the fuild fills the space between the retraction of epidermal cells and the old cuticle. Simultaneosly, new cuticle is sectreted. Ecdysis occurs as well as the casting off from old cuticle. New cuticle becomes scletorized (exocuticle) and endocuticle may continue to be deposited.