Hexapoda - Insecta

Question 1

Hexapoda

Answer 1

The largest group of animals (~ 1,000,000 described).
Massively successful! i.e. they have occupied most terrestrial environments.
They are of great ecological importance and for humans also.

Question 2

Ecological importance of Hexapoda

Answer 2

Pollinators
Natural enemies (of other arthropods)
Food webs
Nutrient recycling / detritivory

Question 3

Social importance hexapoda

Answer 3

Pests of plants & animals
Vectors of disease

Question 4

Insecta morphology- the basics

Answer 4

Distinctive features (at a glance)
3 pairs of legs
3 body sections (‘tagmata’)
Usually, 2 pairs of wings on the thorax.
1 pair of compound eyes;
1 pair antennae
Tracheal system for gas exchange. - Spiracles link to a pit and then the tracheal system

Question 5

Insecta excretion and Water balance

Answer 5

Malpighian tubules lie in the hemocoel.

Question 6

Insecta reproduction & copulation

Answer 6

Spermatophores are typic
The ‘inflatable’ aedeagus is inserted in the female bursa.
The spermatophore is deposited.
Sperm are released from the spermatophore where they are stored in the spermathecae

Question 7

Extreme morphological diversity in insect genitalia

Answer 7

Many possible hypotheses for diversity- special barriers- speciation- sexual conflict- mate competition

Question 8

Insecta Eggs

Answer 8

Eggs are coated with shell-like membrane.
There are 1 or more tiny openings were sperm enter (micropyles).
Eggs are laid through an ovipositor. (8 or 9th segment).

Question 9

Insecta Nutrition

Answer 9

Insects are adapted to many diets.
Modifications of mouthparts reflect how food is ingested.
Mandibles function in cutting & tearing; maxillae and labium function in food handling.

Question 10

Different types of mouthparts

Answer 10

Piercing mouthparts (maxillae & mandibles)
Sucking mouthparts (maxillae form a tube in Lepidoptera)
Knifelike mandibles
Non-biting flies use a sponge like labium.

Question 11

Comparisons with other Arthropods

Answer 11

Cuticle (waxy) also in other terrestrial groups but calcified in Diplopoda & Crustacea
Spiracles- shared with Myriapods (open) & chelicerata
Excretion Malpighian tubules also present in Chelicerata but evolved independently
Internal fertilization / copulation (convergently evolved in with Araneae but not all Chelicerata or myriapoda)

Question 12

How are they different from other Arthropods?

Answer 12

So many of them
Wings
Herbivory
Larval stages with distinct niches
Adaptability – eg mouthparts

Question 13

Wingless hexapods

Answer 13

“Apterygotes” 5 orders- not very speciose no true metamorphosis not a monophyletic group

Question 14

Ametaboly

Answer 14

no true metamorphosis
eg. Primitive Zygentoma silverfish

Question 15

Hemimetabolous insects

Answer 15

hemimetaboly - flight

Question 16

Hemimetabolous insects

Answer 16

hemimetaboly - flight

Question 17

Holometabolous insects

Answer 17

mnemonic : “whole” metamorphosis

Question 18

Insect wings

Answer 18

Are membranous and very unlike other jointed appendages.
Unlike Vertebrate wings they are not modified legs – so how have they evolved?

Question 19

Exite / endite hypothesis

Answer 19

wings from gill branch on biramous limb

Question 20

Epicoxal hypothesis

Answer 20

modified abdominal gills

Question 21

Paranotal hypothesis

Answer 21

wings from scratch

Question 22

Wings

Answer 22

Primitive wings are held outstreched (i.e. dragonflies).
The evolution of sclerites has enabled insects to fold the wings over the abdomen.

Question 23

Flight

Answer 23

Insect muscles are very powerful.
Within the muscle cells the mitochondria are huge.
At low body temperature, metabolic rate is low.
Therefore many flying insects have to ‘warm-up’ to enable flight.

Question 24

Coevolution

Answer 24

(reciprocal evolutionary changes brought about by interactions between species) of plants and insects