1. Myriapods and Insects CH 14 Subphylum Mandibulata (continued from Crustacea)

2. Myriopods: “myriad of legs”
Centipedes
(Chilopoda)
Millipedes
(Diplopoda)
Similar to insects in many ways:
--Uniramous appendages, trachea, excretory system
--Antenna, mandibles, 1st &2nd maxilla,
maxilliped as poison gland in centipedes
--Two distinct body regions: head-trunk
-- Millipedes and centipedes found in late Cambrian marine fauna; considered two independent invasions of land

3. More on Myriapods: Fangs ---
All terrestrial, mostly nocturnal, relegated to moist conditions in forest, moist soils rotting logs
The cuticle is not waxy and allows considerable water loss. Also, spiracles of tracheal system are unable to close during respiration
Centipedes: maxillipeds as fangs; night hunters
Millipedes: herbivores; fused segments, 2 pr of leg per
“leggiest millipedes” 750 pr of legs
Fangs ---

4. Super Class Hexapoda (6 legged arthropods) Class Entognatha
Class Insecta
A. Introduction
B. Basic characteristics
What distinguishes insects?
C. Insect Reprod. & Early Development
E. Metamorphosis
F. Exoptergygota and Endopterygota
Hormonal Control of Metamorphosis
Insect Societies

5. Class Entognatha Diplura (questionable affinity) Protura Collembolla
(two-pronged bristletails)
Diplura (questionable affinity)
Protura
Collembolla
Wingless
- Mouthparts within a
special pouch on the head
Without metamorphosis
Branched off before the
evolution of insects
(springtails)

6. Class Insecta Thysanura (silverfish) - Considered the most
primitive true insects
Wingless
Without metamorphosis

7. Familiar Animals Great diversity of Flying Insects (Pterygota)
(Japanese beetle)
(black fly)
Familiar Animals
Order Coleoptera
(360,000 species)
Order Diptera
(150,000 species)

8. Less Familiar Organisms
biting lice
(secondarily
wingless parasites)
Order Mallophaga
(2500 species)

9. Diversity Exotic animals Order Lepidoptera Meets the Order Mantoidea
(160,000 species)
Meets the Order Mantoidea
(2,000 species)

10. Malaria, plague, typhoid and yellow fever……. Benefits:
...Vectors of disease
…as pests
Female Anopholes
Mountain pine beetles
Malaria, plague, typhoid and
yellow fever…….
Benefits:
as predators of other insects
(parasitoid dipterans, hymenopterans)
as producers…honeybees, silkworms
as pollinators of plants
In western North America, the current outbreak of the mountain pine beetle and its microbial associates has destroyed wide areas of lodgepole pine forest, including more than 16 million of the 55 million hectares of forest in British Columbia. The current outbreak in the Rocky Mountain National Park began in 1996 and has caused the destruction of millions of acres of ponderosa and lodgepole pine trees. According to an annual assessment by the state's forest service, 264,000 acres of trees in Colorado were infested by the mountain pine beetle at the beginning of This was much smaller than the 1.15 million acres that were affected in 2008 because the beetle has already killed off most of the vulnerable trees (Ward).[1]
Unusually hot, dry summers and mild winters throughout the region during the last few years, along with forests filled with mature lodgepole pine, have led to an unprecedented epidemic. The largest forest insect blight ever seen in North America

11. Success of Insects
- 35 to 40 orders, million species 2-3 thousand described every year; outnumber all other animal species combined
# of individuals in most species is high e.g. locust
- found in practically every major habitat
(one exception is the deep sea)
- great economic importance

12. Reasons for Success High reproductive potential
termite queen lays 200,000 eggs/day
- Small size: most insects mm in length large numbers for any given food supply
- Metamorphosis: larva or nymph and the adult stage do not compete for food
Wings and Flight: gain in dispersal, escape predation, exploit resources
- Exoskeleton

13. Class Insecta = Hexapoda
A. Introduction
B. Basic characteristics
What distinguishes insects?
C. Insect Reprod. & Early Development
E. Metamorphosis
F. Exoptergygota and Endopterygota
Hormonal Control of Metamorphosis
Insect Societies

14. Characteristics Uniramous appendages
- Four cephalic appendages: antenna, mandibles
1st maxilla, labium (fused 2nd maxilla)
(tutorial on insect mouthparts )
- Most appendages are uniramous (but evolved from
polyramous, possibly even biramous types)

15. Insect Body Plan
- 3 Tagma: Head, thorax, abdomen; thorax as 3 segments, pro, meso, metathorax
1 pair of legs per thoracic segment; wings in meso and metathorax (1 pair on each)
Tutorial on insect leg segments
- Abdomen usually with 11 segments; repro. structures;
Abdominal appendages have been lost

16. Respiratory system of spiracles and trachea
System of tubes that deliver oxygen directly to flight muscles and other cells!!
Air taken into spiracles (by action of abdominal muscles) into tracheal tubes then to tracheoles and finally to individual cells.
Respiration is independent of blood circulation

17. Tracheoles
Trachea
Spiracle
Muscle
fibers

18. Excretory and osmoregulatory Malpighian tubules
Hollow tubes between hemocoel, (where waste is collected) and the gut where waste is removed.
Distally K Urate in dissolved form enters the tubule.
Highly
alkaline
Acidic
As pH drops proximally,
uric acid is formed, water
and potassium is reabsorbed.
Waste is in the form of a crystal, uric acid and water is thus conserved.

19. Class Insecta = Hexapoda
A. Introduction
B. Basic characteristics
What distinguishes insects?
C. Insect Reprod. & Early Development
E. Metamorphosis
F. Exoptergygota and Endopterygota
Hormonal Control of Metamorphosis
Insect Societies

20. Reproduction Insects are dioecious (separate sexes)
Sperm transferred in a specialized container (spermatophore)
Fertilized Eggs Require protection:
oviposition in water
or in other insects
or in plant tissues

21. - After fertilization, nuclei duplicate and migrate to the perimeter of the embryo, cellularize and form a blastula
In technical term a syncitial stage becomes cellularized
Link to Video

22. Superficial cleavage in a Drosophila embryo
Superficial cleavage in a Drosophila embryo. The early divisions occur centrally. The numbers refer to the cell cycle. At the tenth cell cycle (512-nucleus stage 2 hours after fertilization), the pole cells form in the posterior, and the nuclei and their cytoplasmic islands (“energids”) migrate to the periphery of the cell. This creates the syncytial blastoderm.

23. Reproduction and Development
- Segments begin to develop in sequence resulting in formation of head, thorax and abdominal region

24. Class Insecta = Hexapoda
A. Introduction
B. Basic characteristics
What distinguishes insects?
C. Insect Reprod. & Early Development
E. Metamorphosis
F. Exoptergygota and Endopterygota
Hormonal Control of Metamorphosis
Insect Societies

25. Types of Post-Embryonic Development (metamorphosis)
1. Ametabolous: no larva or nymph
wingless primitive insects
such as springtails and collembolans
Examples :
bristletails
silverfish
Miniature adult; without any major change in form

26. Dragonfly naiad 2. Hemimetabolous mayfly
Immature aquatic stage, or naiad; similar to the adult but the wings are not fully developed.
Wing pads can be seen on advanced instars
Common orders : Ephemeroptera (mayflies)
Odonata (Dragon Flies, damsel flies),
Plecoptera (stone flies)

27. 3. Paurometabolous: similar
to hemimetabolous
Usually involves terrestrial forms
such as grasshopper.
The immature stage is the nymph

28. -- Young is different from adult in nearly every respect.
4. Holometabolous
-- Young is different from adult
in nearly every respect.
-- Called a larva; it must pupate
and undergo a profound
metamorphosis to the adult
stage or imago.
-- The pupa in beetles is called a grub, in flies a maggot, crysallis for butterflies
Why Imago? “Apparition” ?
mosquito
larva
pupa

29. Types of Development in Insects
Ametabolous
Hemimetabolous
Paurometabolous
Holometabolous

30. Imaginal Discs in Holometabolous Development
Imaginal discs have not been found in animals with incomplete metamorphosis

31. Class Insecta = Hexapoda
A. Introduction
B. Basic characteristics
What distinguishes insects?
C. Insect Reprod. & Early Development
E. Metamorphosis
F. Exoptergygota and Endopterygota
Hormonal Control of Metamorphosis
Insect Societies

32. Insect hormonal control of metamorphosis
PTTH produced by cells in the brain enters the corpora cardiaca (neurohemal organs associated with the aorta)
Increasing PTTH levels in the blood induce the Prothoracic gland to produce ecdysone
Action of ecdysone is modified by juvenile hormone (JH) from the corpora allata; JH suppresses expression of “adult genes”
- What triggers cessation of JH production? Genetics.
JH in red
Prothoracicotrophic hormone (PTTH)

33. PTTH stimulates the prothoracic gland to produce ecdysone.
Hormonal regulation of metamorphosis.
The Corpus cardiacum secretes prothoracicotropic hormone.
PTTH stimulates the prothoracic gland to produce ecdysone.
Ecdysone is released periodically during molting (ecdysis) of the larva.
The Corpus allatum secretes juvenile hormone. High levels of JH signal leads to another larval stage, while low levels of JH promotes the formation of a pupa and metamorphosis.

34. Insect Social Systems --Truly Social Insects (Eusocial) include:
-- all ~9500 ant species
-- honeybees, a few wasps
Hymenoptera
-- termites
-- Colonies are made up of Castes in all 3 groups:
bees: workers (all sterile females), queen, drones

35. Insect Social Systems --Truly Social Insects (Eusocial) include:
-- all ~9500 ant species
-- honeybees, a few wasps
Hymenoptera
-- termites
-- Colonies are made up of Castes:
ants: workers, soldiers, queen, males
queens control sex of offspring by pheromones
Waggle dance of the honeybee

36. Insect Social Systems
male
worker
Flying female
soldier

37. Insect Social Systems Inclusive fitness: Haplodiploidy:
Males are 1N, females 2N
There is an asymmetrical degree of relationship
Mothers are 1/2 related to daughters
Sisters are 3/4 related to each other
But termites, snapping shrimp also eusocial yet not haplodiploid so other adaptive values may exist 1