Antennata

Question 1

What type of group is antennata?

Answer 1

Paraphyletic - includes a common ancestor but not all of its descendents

Question 2

What groups does Antennata contain?

Answer 2

Insects and Myriapods
NOT crustaceans
Grouped because they’re morpho logically similar but not more closely related genetically

Question 3

Facts about insects

Answer 3

Largest and most diverse group of metazoans
2 million known species
350,000 species of beetles (25% of all known life forms)

Question 4

Features of Antennata

Answer 4

• 1 pair of antennae
• 1 pair of mandibles
• 2 pairs of maxillae
• Uniramous limbs - they comprise of a single series of segments attached end to end as opposed to a biramous limb which branches
• Head separate from trunk

Question 5

Features of class Insecta

Answer 5

• Body divided into head thorax and abdomen
• 3 pairs of legs on thorax
• No appendages on abdomen
• Adults usually have 2 pairs of wings on thorax

Question 6

Insecta: locust

Answer 6

• Thorax in 3 segments
• Abdomen has 11 segments
• Compound eye made of thousands of repeating units or lenses, which are called ommatidia. Each ommatidia functions as a separate visual receiver. Image is mosaic from all ommatidia
• Locusts have relatively few ommatidia so low resolution image
• Three ocelli (simple eyes that use a single lens to collect and focus light) for light detection only
• Sclerotised mandibles

Question 7

Insect exoskeleton

Answer 7

• Provides insects with a light and strong form of support for their internal organs and a rigid frame for muscular attachments and action required in flight and walking
• Chitin rods in protein matrix provide resistance to tearing
• Spiral layering of chitin rods gives extra strength
• ‘Tanning’ is protein to sclerotin - provides rigidity
• Monolayer of wax molecules for waterproofing
• Insect eggs have cuticle coat when laid to prevent desiccation
• Resilin is associated with the cuticle, which is an elastic and rubber-like protein with 100% elasticity. The energy stored during its compression is released when returned to its original state. Blocks of resilin are found in the thorax, and are of importance in the articulation of wings

Question 8

Insect thorax and abdomen

Answer 8

• Insects have a dorsal vessel (the heart) which consists of a longitudinal tube running the length of the thorax and abdomen on the dorsal side of the body wall
• It has a central nerve cord which runs longitudinally through the thorax and the abdomen on the ventral side
• The muscles are attached to the inside of the body wall by ridge-like ingrowths of the exoskeleton called apodemes, which provide attachment points and support internal organs
• There are extensor and flexor muscles moving the legs

Question 9

Insect walking

Answer 9

• Insects have 6 legs arranged in stable tripods
• The insect walks by alternating tripods
• The first right foot, second left food and third right foot are on the ground at the same time, creating a tripod. The other three are moving forward taking the next step

Question 10

Insect wings

Answer 10

• First flying animals
• Not homologous to previous appendages - new evolutionary development (apomorphy)
• Most insects have two pairs of wings
• Most insects flap the wing pairs in synchrony, and the wings overlap or are hooked together by special structures (like in bees)
• Sometimes the wings move out of phase with each other (eg damsel fly)
• Wings are evaginations (outpockets) or cuticle
• Between the upper and lower layer are sclerotised veins which contain trachea, vessels for haemolymph and nerve fibres. They are not true veins
• The wing veins are arranged in a fixed pattern according to the species, which are very useful in taxonomy and used for identification of similar insects

Question 11

What are apterygotes?

Answer 11

Primitively wingless insects which separates from other insects before the evolution of wings

Question 12

What insects only have wings at certain points in their life cycle

Answer 12

Ants and termites, when they need to breed or start a new colony

Question 13

What insects have lost their wings secondarily?

Answer 13

Lice and fleas

Descended from winged insects but lost theirs

Question 14

Beetle wings

Answer 14

Have a modified forewing which provides protection of the hindwing - a sclerotised, hardened protective cover called the elytra. It covers the hindwings when the beetle isn’t flying

Question 15

Dipteran flies wings

Answer 15

The hindwing is reduced to a small stalk called the haltere, which acts as a balance organ during flight. The forewing is used for flight

Question 16

Evolution of insect wings

Answer 16

• Fossils show wings to be 300 million years old
• It is thought that wings evolved as a lateral aerodynamic flap, allowing the insect to land safely when falling and to land the correct way up
• Paranotal lobes (aerodynamic flaps) have been found in fossilised insects
• The enlargement of paranotal loves with supporting veins would have allowed gliding, and this would have been followed by the evolution of hinges, allowing the lobes to flap

Question 17

What is the epicoxal hypothesis of wing evolution?

Answer 17

Suggests that wings evolved from the moveable tracheal gills found in aquatic immature stages of some insects such as mayflies

Question 18

What is the endite-exite hypothesis of insect wing evolution?

Answer 18

Suggests that wings evolved from appendages on primitive arthropod limbs

Question 19

Evolution of insect wing veins

Answer 19

• There has been a process of simplification of wing veins during evolution
• Dragonflies are more primitive and have very complex veins
• Recently evolved insects such as bees and wasps have much simpler venation
• The more derived insects also have evolved additional hinges at the wing bases which allow the wings to fold back over the abdomen, keeping the wings safe when insects are not flying and allowing new habitats to be explored

Question 20

Wing movement in dragonflies

Answer 20

• Legs and antenna moved by direct action of muscles
• Wing movement involves the indirect action of muscle
• Wings moved by both direct and indirect action of muscle
• To lower the wing, a direct acting muscle called the basilar muscle contracts. This directly pulls the wing downwards. In doing this, the top of the thorax (the notum) is pushed up
• To raise the wing, the indirect dorsoventral muscle contracts, causing the notum to be depressed, and pushing the wing upwards

Question 21

Wing movement in dipteran flies

Answer 21

• Both upward and downward wing movements created by indirect muscles which act on the wings but changing the shape of the notum
• The wings are moved upwards by contraction of the dorsoventral muscle (depressing the notum) similar to in dragonflies
• To move the wing downwards, the longitudinal muscles within the thorax contract, causing the notum to arch or be lifted up. This indirectly results in the hinge of the wing popping up, forcing the wing downwards by rotation about the pivot point

Question 22

Impacts of flight on insect life

Answer 22

• Energetically expensive
• Insects are the only poikilothermic fliers
• When cool, the low metabolic rate of insects imposed limitations on their mobility. To overcome this, some insects (bumblebees, moths) vibrate their wings which generates heat, warming them up. Their flight muscles can therefore be used to generate warmth
• Flight is used for dispersal, escape and colonisation
• Insects have huge mitochondria in their flight muscles

Question 23

Insect tracheal system

Answer 23

• Insects do not have lungs, but instead a tracheal system
• Oxygen delivered directly to organs by tubes
• Holes in the exoskeleton called spiracles join tracheal system to air. One spiracle per abdomen segment
• Spiracles open up into an atrium which has small hairs and spines to reduce dust and debris entering insect
• Tubes called trachea
• Trachea reinforced with rings of sclerotised cuticle so they don’t collapse
• Ventilation achieved by passive diffusion and flushing the trachea with abdominal movement
• Haemolymph directly bathes their organs
• In flight muscles trachea branch into tiny tracheole tubules to allow gas exchange of muscles

Question 24

Insect feeding

Answer 24

• Many different mouthparts
• Many insects feed on different foods at different stages of their lives. For example, the cabbage butterfly in its larval stages feeds on cabbage, but the adult feeds on nectar and has completely different mouthparts
• This reduces competition between juveniles and adults

Question 25

What is the condition where sheep add infected with blowfly larvae?

Answer 25

Myiasis

They feed on the live flesh of the sheep

Question 26

Insect internal fertilisation

Answer 26

• Fertilisation must usually be internal as the eggs have a protective cuticle that would be hard to fertilise through
• The male passes spermatozoa to the female in a package called the spermatophore
• The female stores the sperm in storage organs called spermathecae, until her eggs mature
• She then releases the sperm from the spermathecae and fertilises the eggs as they are laid
• Great reproductive diversity: some show parental care such as earwigs and tunnelling dung beetles
• Some are viviparous, such as aphids and flies
• Some are parthenogenic (can produce young without mating) such as aphids and ants
• Some insects only have one reproductive individual per colony - these are social insects (ants, termites, bees, wasps)

Question 27

Insect ametabolous life cycle

Answer 27

• Found in insects such as the wingless silverfish

- No metamorphosis, only simple development

Question 28

Three types of insect life cycle

Answer 28

1) Ametabolous
2) Hemimetabolous
3) Holometabolous

Question 29

Insect hemimetabolous life cycle

Answer 29

• Found in insects which have a developmental system where the juveniles are more or less similar to adults
• After each moult, the juveniles get bigger
• The final moult is where there is development of the reproductive organs, adult colouration and full development of the wings
• The larvae and adults live in the same habitats and eat the same food

Question 30

Insect holometabolous life cycle

Answer 30

• Involve full metamorphosis
• Most derived type of life cycle
• Adults very different from larvae, and have different names
• The larvae feed on different food to the adults and lack compound eyes and antenna. The mouthparts are usually completely different. Wing pads are not present
• Through several moults, the larvae becomes a pupa

Question 31

What is the pupa stage in butterflies?

Answer 31

This stage is immobile and cryptic. Dramatic reorganisation occurs into the adult form

Question 32

What fraction of flowering plants rely on insect pollination?

Answer 32

2/3

including crops

Question 33

What are other contributions made by insects to ecosystems (besides pollination)

Answer 33

• Nutrient cycling
• Soil formation
• Soil fertility
• Decomposition
• Pest control
• As a good source for other species

Question 34

How many chemicals are now used for pest control?

Answer 34

15,000 in 35,000 mixtures