1. Arthropoda 5 major lines of arthropod evolution: Trilobitamorpha
Cheliceriformes
a. Merostomata
b. Arachnida
Crustacea
Hexapoda
a. Entognatha
b. Insecta
Myriapoda

2. Sub phylum Hexapoda Diverse group (~1000 families)
Twice as diverse as all other animal taxa combined
Co-evolved with angiosperms
Flower morphology / pollinators
Herbivory / 2°plant compounds/resistance and specialization
Parasitoidism (20% of insects are parasitoids)

3. Hexapoda Mostly terrestrial
In every habitat except the subtidal marine habitat – competition from crustacea?
3 tagma: head, thorax, abdomen
3 pairs of legs, and usually 2 pairs of wings on thorax
no abdominal appendages

4. Major contributors to insect success
Arthropod body plan
Small size
Resistance to desiccation
Trachea
Waterproof cuticle, egg shell
Malphigian tubules
Flight
Rapid dispersal
Escape from predators
Access to distant food, mates
Holometaboly:
Larvae and adults occupy separate niches (most speciose groups are all holometabolous: coleoptera, lepidoptera, hymenoptera, diptera)

5. Holometabula Hemimetabolous development
e.g. Odonata, Orthoptera, Blattodea
Mantodea, Hemipteroids
Incomplete metamorphosis
Wing pads present in pre-adult
Larvae often resemble small adults
Holometabolous development
e.g. coleoptera, lepidoptera, diptera, hymenoptera
Complete metamorphosis
Inactive pupal stage
Larvae do not
resemble parents
eat the same things as parents
live in the same habitat as parents

8. Big picture
Hugely important ecologically as pollinators (2/3 of all flowering plants), detritivores, herbivores
Important economically and socially (to humans) as disease vectors (fleas, lice, bedbugs, biting flies), crop pests (and also as pollinators and biological control agents)

9. Hexapoda 2 classes: Entognatha (mouth parts recessed),
Insecta (mouthparts are ectognathous = exposed and projecting from head capsule)

10. Hexapod origins From aquatic crustacean ancestor
Probably freshwater
Winglessness (apterygota) is primitive condition

11. “Pterygota” Flight evolved 300-400 mya
Wings = outpocketings of exoskeleton
Origins of wings? Multiple hypotheses:
Used for thermoregulatory purposes then later co-opted for flight?
Used to stabilize body during jumping?
Modified from external gills? (genetic similarities with crustacean gill structures)

12. Requirements for flight
Musculature
Striated
Attached to strong exoskeleton with flexible joints
Small body size
Impervious to water loss
Efficient internal physiology for gas exchange (trachea), nutrient storage and distribution
Well-developed and integrated sensory organs to regulate rapid movement

13. Low rate of wing-flapping
Odonata, ephemeroptera, orthoptera, lepidoptera
Flapping rate limited by firing rate of neurons
High rate of wing-flapping
Diptera, hymenoptera, coleoptera
Use elastico-mechanical properties of exoskeleton to stimulate stretch receptors to produce self-sustaining flight