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

1. Myriapods and InsectsCH 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: 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 (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. 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 (160,000 species) Meets the Order Mantoidea (2,000 species)

10. ...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

11. Success of Insects • - 35 to 40 orders, 0.75 - 1.5 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 1-2.5 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. 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. www.ncbi.nlm.nih.gov

23. Reproduction and Development - Segments begin to develop in sequence resulting in formation of head, thorax and abdominal region http://www.cals.ncsu.edu/course/ent425/tutorial/embryogenesis.html

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. 2. Hemimetabolous mayfly Dragonfly naiad • 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. 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 JH in red • PTTH produced by cells in the brain enters the corpora cardiaca (neurohemal organs associated with the aorta) • Increasing PTTH levelsin 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. Prothoracicotrophic hormone (PTTH)

33. 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