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CHAPTER 21

CHAPTER 21. Hexapods. Diversity and Characteristics. Subphylum Hexapoda Members named for the presence of six legs Have 3 tagmata Head Thorax Abdomen Appendages attach to head and thorax Main class within Hexapoda

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CHAPTER 21

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  1. CHAPTER 21 Hexapods

  2. Diversity and Characteristics Subphylum Hexapoda • Members named for the presence of six legs • Have 3 tagmata • Head • Thorax • Abdomen • Appendages attach to head and thorax • Main class within Hexapoda • Insecta - (ex. Ladybugs, grasshoppers, butterflies, walking stick, ect.) • Pterogotes: winged insects • Apterogotes: wingless insects

  3. Class Insecta • Diversity • Most diverse and abundant of all arthropods • Number of known species estimated at 1.1 million, but estimated that there may be as many as 30 million species worldwide • Adaptive Traits • Flight and small size makes insects widely distributed • Well-protected eggs withstand rigorous conditions • Most structural modifications are in wings, legs, antennae, and mouthparts • Hard, protective exoskeleton well-adapted to life in desert regions - hold in water

  4. Class Insecta External Form and Function There are MANY Variations in Body Forms • Exoskeleton composed of complex plates, or sclerites, connected by hinge joints • Muscles attaching sclerites allow precise movement • Head • Usually equipped with pair of large compound eyes • One pair of antennae varies greatly in • Function in touch, taste, hearing • Mouthparts consist • Pair of mandibles and maxillae • Tongue like Hypopharynx (determines how it feeds.) - Proboscis

  5. Different Insect Antennae

  6. Class Insecta • Thorax • Consists of 3 parts • Each section has a pair of legs • Wings • located on the thorax • Veins serve to strengthen the wing • Vein pattern used to identify insect taxa

  7. Class Insecta • Legs and adaptations • Walking legs end in terminal pads and claws • Hindlegs of grasshoppers and crickets are enlarged for jumping • Forelegs of praying mantis allow it to grasp prey • Honeybees have leg adaptations for collecting pollen

  8. Hindleg of a Grasshopper: Muscle attached to internal wall of exoskeleton

  9. Praying Mantis front legs are used to grasp prey

  10. Adaptations in Bee Legs: Spur removes wax, Pollen brush help remove pollen collected on the body Pollen comb brushes off pollen collected on other leg Pollen packer presses pollen into pollen basket Bee carries as much pollen as possible back to her hive

  11. Giant Horned Beetle: Process from head is used to lift or pry competition from resources. (Usually competition is same species) Walking Sticks Mating: They have many predators, despite camouflage

  12. A female Wasp uses her abdomen to thrust her ovipositor into the wood to make a burrow to lay her eggs. The larva will feed on the wood

  13. Class Insecta • Locomotion: Walking • Insects walk using first and last leg on one side and middle leg on the opposite side in alteration with the reverse • Provides stability • A water strider has non-wetting footpads that do not break the surface water tension • Flight and wings • Insect wings not homologous with bird and flying mammal wings • Insect wings are outgrowths of cuticle from the thoracic segments • Most flying insects have 2 pairs of wings • Diptera (true flies) have one pair • Non-reproductive ants and termites are wingless

  14. Water strider: Supported by the Water’s surface tension

  15. Order Diptera: House Fly Only one set of wings, Contaminated with over 100 pathogens

  16. Class Insecta • Flight Muscles of Insects • Direct flight muscles attach to wing directly • Indirect flight muscles alter the shape of the thorax to cause wing movement • Flight Muscle Contraction • Wing beats may vary • 4/second in butterflies • 1000/second in midges (small flies)

  17. Class Insecta Internal Form and Function • Digestive System • Foregut • Mouth with salivary glands, esophagus, crop, and gizzard • Midgut (similar to small intestine) • Primary site of digestion and absorption • Ceca (villi) may increase digestive and absorptive area • Hindgut (similar to large intestine) • Primarily a site for water absorption

  18. Internal Structure of Female Grasshopper

  19. Class Insecta • Most feed on plant tissues or juices and are herbivorous • Many caterpillars are specialized to eat only certain species of plants • Many beetles and other insect larvae eat dead animals • Some are predaceous

  20. Parasitic Insect: Flea

  21. Parasite: Guinea Pig Lice

  22. Parasite: Human Lice

  23. B: A tiny wasp laid eggs in Hornworm Caterpillar. Pupae emerge, Caterpillar dies A: Larval Stage of Tomato Hornworm

  24. A: Chewing Mouthparts B: Sucking Mouthparts - Fascicle pierces D: Sucking Mouthparts Mandible absent, Maxillae form long proboscis E: Sponging Mouthparts Lap liquid, Liquefy food

  25. Class Insecta • Circulation - Open Circulation • Tubular heart moves hemolymph forward through aorta • Heartbeat is a wave • Accessory pulsing organs help move hemolymph into wings and legs tissue

  26. Class Insecta • Gas Exchange • Gas exchange while preventing water loss • Tracheal system • Network of thin-walled tubes that branch throughout the insect body • Spiracles open to the tracheal trunks • 2 spiracles on thorax and 7–8 on abdomen • Valve on the spiracle • Reduces on water loss and may serve as a dust filter

  27. Prevent collapse Spiracle Opening Tracheal System: System provides gastransport without use of oxygen-carrying pigments

  28. Excretion and Water Balance • Insects utilize Malpighian tubules

  29. Class Insecta • Sense Organs • Mechanoreception • Touch, pressure, vibration, etc. are detected by sensilla • May be a single hair-like seta or a complex organ • Distributed widely over antennae, legs, and body • Auditory Reception • Sensitive setae or tympanal organs detect airborne sounds • Organs in legs can detect vibrations of substrate • Chemoreception • Some insects can detect odor from several kilometers away

  30. Class Insecta • Visual Reception • 2 types of eyes: simple (sense light) and compound (sense images) • Most larval stages have simple • Adult stages have compound • Some insects can detect color

  31. Class Insecta • Reproduction • Parthenogenesis occurs predominantly in some Hemiptera (true bugs) and Hymenoptera (ants, wasps, bees) • Sexual reproduction is the norm • Sexes are separate • Sexual Attraction • Females secrete a pheromone to attract males from a great distance • Fireflies use flashes of light to detect mates • Some insects use sounds, color signals, and other courtship behaviors

  32. Grasshopper Reproduction Damselflies Reproduction

  33. Class Insecta • Fertilization usually internal • Sperm may be released directly or packaged into spermatophores • Female may only mate once and store sperm to fertilize eggs throughout her life • Females may lay a few eggs and provide care of young, or lay huge numbers • Butterflies and moths must lay eggs on the host plant if the caterpillars are to survive • Wasps may have to locate a specific species that is the only host to their young

  34. Mosquito Eggs laid in a “raft”on water Mosquito Larva

  35. Class Insecta • Metamorphosis and Growth • Various forms of metamorphosis produce degrees of change among different insect groups • Most insects change form after hatching from egg • Each stage between molts is called an instar • Insects develop wings during the last stage

  36. Ecdysis in cicada: Wings form after last molt Adult Cicada

  37. Stonefly and Damselfly Both have Aquatic Nymphs

  38. Class Insecta • Incomplete (Hemimetabolous) Metamorphosis • Grasshoppers, cicadas, mantids, true bugs, mayflies and dragonflies exhibit this metamorphosis • Young are called nymphs • Stages are egg-nymph-adult. All stages look equivalent, vary in size

  39. Incomplete Metamorphosis: Body forms are similar throughout cycle Young are called nymphs Incomplete Metamorphosis: grasshoppers, cicadas, mantids, terrestrial bugs, mayflies, stoneflies, dragonflies, and aquatic bugs 21-42

  40. Class Insecta • Complete (Holometabolous) Metamorphosis • About88% of insectsundergo complete metamorphosis • Larva, pupa, and adult vary in body plan • Larvae and adults often live in completely different environments • No competition • After several larval instars • Larval moth or butterfly becomes a pupa inside a cocoon or chrysalis • Pupae often pass the winter in this stage • Final molt occurs and the adult emerges in spring • Stages are egg-larva-pupa-adult

  41. Complete Metamorphosis: Multiple life stages 21-44

  42. Class Insecta • Diapause • Period of dormancy in the annual life cycle that is independent of conditions • Winter dormancy: hibernation • Summer dormancy: estivation • Any stage (eggs, larvae, pupae, or adults) may remain dormant to survive adverse conditions • Always occurs at end of an active growth stage • Insect is then ready for another molt

  43. Class Insecta • Defense • Protective coloration, warning coloration, and mimicry are protective adaptations • Stink bugs and others have repulsive odors and tastes • Some insects are aggressive (e.g., bees and ants) • The monarch caterpillar incorporates a poisonous substance from its food plant, milkweed • The bombardier beetle can spray an attacking enemy with irritating chemicals

  44. Mimicry in butterflies: A: Monarch - is distasteful B: Viceroy Butterfly - mimics monarch to avoid predators

  45. Crypsis - Camouflage in shape or coloration A: Resembles a dead leaf (moth) B: Resembles a tree branch (treehopper) C: Resembles leaves (Katydid)

  46. Behavior and Communication Dung Beetles: Chew off a bit of dung, Roll it to site to bury, Eggs laid in ball, Larvae feed on dung

  47. Class Insecta Behavior and Communication • Pheromones • Chemicals secreted by one individual to affect the behavior of another individual • Attract the opposite sex, trigger aggregation, fend off aggression, and mark trails • Bees, wasps, and ants can recognize nestmates and signal an alarm if strangers enter the nest • Sound Production and Reception • Sounds are used as warning devices, advertisement of territory, and courtship songs. • Crickets chirp for courtship and aggression

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