1. 21-1 CHAPTER 21 Hexapods Hexapods

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3. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-3 Diversity and Characteristics Subphylum Hexapoda Members named for the presence of six legs Members named for the presence of six legs All legs are uniramous All legs are uniramous Have 3 tagmata Have 3 tagmata Head Head Thorax Thorax Abdomen Abdomen Appendages attach to head and thorax Appendages attach to head and thorax Two classes within Hexapoda Two classes within Hexapoda Entognatha Entognatha Insecta Insecta

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5. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-5 Characteristics of Entognatha Characteristics of Entognatha Small group characterized by bases of mouthparts enclosed within the head capsule Small group characterized by bases of mouthparts enclosed within the head capsule 3 orders: Protura, Diplura, and Collembola 3 orders: Protura, Diplura, and Collembola Protura and Diplura Protura and Diplura Tiny, eyeless, and inhabit soils or dark, damp places Tiny, eyeless, and inhabit soils or dark, damp places Collembola Collembola Commonly called springtails because of ability to leap Commonly called springtails because of ability to leap Animal 4 mm long may leap 20 times its body length Animal 4 mm long may leap 20 times its body length Members live in soil, decaying plant matter, on freshwater pond surfaces, and along seashore Members live in soil, decaying plant matter, on freshwater pond surfaces, and along seashore Can be very abundant, reaching millions per hectare Can be very abundant, reaching millions per hectare Diversity and Characteristics

6. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-6 Characteristics of Insecta Characteristics of Insecta Enormous class whose members have ectognathous mouthparts, however, bases of mouthparts lie outside the head capsule Enormous class whose members have ectognathous mouthparts, however, bases of mouthparts lie outside the head capsule Pterogotes: winged insects Pterogotes: winged insects Apterogotes: wingless insects Apterogotes: wingless insects Diversity and Characteristics

7. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-7 Class Insecta Diversity Diversity Most diverse and abundant of all arthropods 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 Number of known species estimated at 1.1 million, but estimated that there may be as many as 30 million species worldwide Continued evolution among modern insects Continued evolution among modern insects Fossil record indicates they are a stable group Fossil record indicates they are a stable group Play major medical and economic roles with humans, and also play critical ecological roles Play major medical and economic roles with humans, and also play critical ecological roles Characteristics Characteristics Ectognathous mouthparts and often two pair of wings on the thoracic region of the body Ectognathous mouthparts and often two pair of wings on the thoracic region of the body Range from less than 1 mm to 20 cm in length Range from less than 1 mm to 20 cm in length Larger insects are tropical Larger insects are tropical

8. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-8 Distribution Distribution Found in nearly all habitats except the sea Found in nearly all habitats except the sea Common in freshwater, brackish water, and salt marshes Common in freshwater, brackish water, and salt marshes Abundant in soils, forest canopies, and can be found in deserts and wastelands Abundant in soils, forest canopies, and can be found in deserts and wastelands Most animals and plants have insects as parasites externally and internally Most animals and plants have insects as parasites externally and internally Adaptive Traits Adaptive Traits Flight and small size makes insects widely distributed Flight and small size makes insects widely distributed Well-protected eggs withstand rigorous conditions and are readily dispersed Well-protected eggs withstand rigorous conditions and are readily dispersed Wide variety of structural and behavioral adaptations gains them access to every possible niche Wide variety of structural and behavioral adaptations gains them access to every possible niche Class Insecta

9. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-9 Adaptability Adaptability Most structural modifications are in wings, legs, antennae, mouthparts, and alimentary canal Most structural modifications are in wings, legs, antennae, mouthparts, and alimentary canal Hard, protective exoskeleton well-adapted to life in desert regions Hard, protective exoskeleton well-adapted to life in desert regions Exoskeleton holds in water, a factor that allows desert survival Exoskeleton holds in water, a factor that allows desert survival Class Insecta

10. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-10 External Form and Function Exoskeleton composed of complex plates, or sclerites, connected by hinge joints Exoskeleton composed of complex plates, or sclerites, connected by hinge joints Muscles attaching sclerites allow precise movement Muscles attaching sclerites allow precise movement Rigidity is due to scleroproteins and not mineral matter Rigidity is due to scleroproteins and not mineral matter Allows for lighter weight body necessary for flight Allows for lighter weight body necessary for flight More homogenous in tagmatization than the variable crustaceans More homogenous in tagmatization than the variable crustaceans Cuticle of a somite is composed of a dorsal notum, a ventral sternum and a pair of lateral pleura Cuticle of a somite is composed of a dorsal notum, a ventral sternum and a pair of lateral pleura Class Insecta

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12. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-12 Head Head Usually equipped with pair of large compound eyes Usually equipped with pair of large compound eyes One pair of antennae varies greatly in One pair of antennae varies greatly in Function in touch, taste, hearing Function in touch, taste, hearing Mouthparts consist Mouthparts consist Labrum Labrum Pair of mandibles and maxillae, Pair of mandibles and maxillae, Labium Labium Hypopharynx Hypopharynx Class Insecta

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14. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-14 Thorax Thorax Consists of the prothorax, mesothorax and metathorax Consists of the prothorax, mesothorax and metathorax Each section has a pair of legs Each section has a pair of legs Wings Wings If two pairs present: located on the mesothorax and metathorax If two pairs present: located on the mesothorax and metathorax Consist of a double membrane Consist of a double membrane Veins serve to strengthen the wing Veins serve to strengthen the wing Vein pattern used to identify insect taxa Vein pattern used to identify insect taxa Class Insecta

15. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-15 Legs Legs Walking legs end in terminal pads and claws Walking legs end in terminal pads and claws Hindlegs of grasshoppers and crickets are enlarged for jumping Hindlegs of grasshoppers and crickets are enlarged for jumping Mole crickets have front legs adapted for burrowing in ground Mole crickets have front legs adapted for burrowing in ground Forelegs of praying mantis allow it to grasp prey Forelegs of praying mantis allow it to grasp prey Honeybees have leg adaptations for collecting pollen Honeybees have leg adaptations for collecting pollen Class Insecta

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19. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-19 Abdomen Abdomen 9 to 11 segments 9 to 11 segments Last is reduced to a pair of cerci Last is reduced to a pair of cerci Larval and nymphal forms may have abdominal appendages lacking in adults Larval and nymphal forms may have abdominal appendages lacking in adults External genitalia usually at end of abdomen External genitalia usually at end of abdomen Variations in Body Form Variations in Body Form Land beetles are thick and shielded Land beetles are thick and shielded Aquatic beetles are streamlined Aquatic beetles are streamlined Cockroaches are flat and live in crevices Cockroaches are flat and live in crevices Antennae vary widely from long to short, plumed to knobbed Antennae vary widely from long to short, plumed to knobbed Class Insecta

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22. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-22 Locomotion: Walking Locomotion: Walking Insects walk using first and last leg on one side and middle leg on the opposite side in alteration with the reverse Insects walk using first and last leg on one side and middle leg on the opposite side in alteration with the reverse Provides stability Provides stability A water strider has non-wetting footpads that do not break the surface water tension A water strider has non-wetting footpads that do not break the surface water tension Power of Flight Power of Flight Insect wings not homologous with bird and flying mammal wings Insect wings not homologous with bird and flying mammal wings Insect wings are outgrowths of cuticle from the mesothoracic and metathoracic segments Insect wings are outgrowths of cuticle from the mesothoracic and metathoracic segments Recent fossil evidence suggests insects may have evolved fully functional wings over 400 million years ago Recent fossil evidence suggests insects may have evolved fully functional wings over 400 million years ago Class Insecta

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24. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-24 Recent fossil evidence suggests insects may have evolved fully functional wings over 400 million years ago Recent fossil evidence suggests insects may have evolved fully functional wings over 400 million years ago Most flying insects have 2 pairs of wings Most flying insects have 2 pairs of wings Diptera (true flies) have one pair Diptera (true flies) have one pair Halteres are reduced wings that provide the fly with balance during flight Halteres are reduced wings that provide the fly with balance during flight Non-reproductive ants and termites are wingless Non-reproductive ants and termites are wingless Lice and fleas have also lost wings Lice and fleas have also lost wings Modifications of Wings Modifications of Wings Wings for flight are thin and membranous Wings for flight are thin and membranous The thick and horny front wings of beetles are protective The thick and horny front wings of beetles are protective Butterflies have wings covered with scales Butterflies have wings covered with scales Caddisflies have wings covered with hairs Caddisflies have wings covered with hairs Class Insecta

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26. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-26 Flight Muscles of Insects Flight Muscles of Insects Direct flight muscles attach to wing directly Direct flight muscles attach to wing directly Indirect flight muscles alter the shape of the thorax to cause wing movement Indirect flight muscles alter the shape of the thorax to cause wing movement Wing is hinged on a pleural process that forms a fulcrum Wing is hinged on a pleural process that forms a fulcrum Insects cause the upstroke with indirect muscles that pull the tergum downward Insects cause the upstroke with indirect muscles that pull the tergum downward Dragonflies and cockroaches contract direct muscles to pull the wing downward Dragonflies and cockroaches contract direct muscles to pull the wing downward Bees, wasps and flies arch the tergum to cause the downstroke indirectly Bees, wasps and flies arch the tergum to cause the downstroke indirectly Beetles and grasshoppers use a combination of direct and indirect muscles to move wings Beetles and grasshoppers use a combination of direct and indirect muscles to move wings Class Insecta

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28. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-28 Flight Muscle Contraction Flight Muscle Contraction Synchronous muscle control uses a single volley of nerve impulses to stimulate a wing stroke Synchronous muscle control uses a single volley of nerve impulses to stimulate a wing stroke Asynchronous muscles stretch antagonistic muscle and cause wing to contract in response Asynchronous muscles stretch antagonistic muscle and cause wing to contract in response Require occasional nervous stimulation Require occasional nervous stimulation Potential energy can be stored in resilient tissues Potential energy can be stored in resilient tissues Wing beats may vary Wing beats may vary 4/second in butterflies 4/second in butterflies 1000/second in midges 1000/second in midges Class Insecta

29. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-29 Wing Thrust Wing Thrust Direct flight muscles alter the angle of wings to twist leading edge to provide thrust Direct flight muscles alter the angle of wings to twist leading edge to provide thrust Figure-8 movement moves insect forward Figure-8 movement moves insect forward Fast flight requires long, narrow wings and a strong tilt, as in dragonflies and horse flies Fast flight requires long, narrow wings and a strong tilt, as in dragonflies and horse flies Class Insecta

30. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-30 Internal Form and Function Digestive System Digestive System Foregut Foregut Mouth with salivary glands, esophagus, crop, and gizzard Mouth with salivary glands, esophagus, crop, and gizzard Some digestion, but no absorption, occurs in crop as salivary enzymes mix with food Some digestion, but no absorption, occurs in crop as salivary enzymes mix with food Gizzard grinds food before it enters the midgut Gizzard grinds food before it enters the midgut Midgut Midgut Primary site of digestion and absorption Primary site of digestion and absorption Ceca may increase digestive and absorptive area Ceca may increase digestive and absorptive area Hindgut Hindgut Primarily a site for water absorption Primarily a site for water absorption Class Insecta

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32. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-32 Most feed on plant tissues or juices and are herbivorous or phytophagous Most feed on plant tissues or juices and are herbivorous or phytophagous Many caterpillars are specialized to eat only certain species of plants Many caterpillars are specialized to eat only certain species of plants Some ants and termites cultivate fungus gardens for food Some ants and termites cultivate fungus gardens for food Many beetles and other insect larvae eat dead animals and are saprophagous Many beetles and other insect larvae eat dead animals and are saprophagous Some species are predaceous on other insects or other animals Some species are predaceous on other insects or other animals Class Insecta

33. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-33 Many species are parasitic as adults and/or larvae Many species are parasitic as adults and/or larvae Many parasitic insects, in turn, have parasites, a condition called hyperparasitism Many parasitic insects, in turn, have parasites, a condition called hyperparasitism Parasitoids live inside a host and eventually kill the host Parasitoids live inside a host and eventually kill the host Important in pest control Important in pest control Class Insecta

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38. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-38 Mouthparts Mouthparts Sucking mouthparts form a tube to pierce tissues of animals or plants Sucking mouthparts form a tube to pierce tissues of animals or plants Houseflies and blowflies have sponging mouthparts Houseflies and blowflies have sponging mouthparts Soft lobes at the tip absorb food Soft lobes at the tip absorb food Biting mouthparts can seize and crush food Biting mouthparts can seize and crush food Class Insecta

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40. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-40 Circulation Circulation Tubular heart in the pericardial cavity moves hemolymph forward through dorsal aorta Tubular heart in the pericardial cavity moves hemolymph forward through dorsal aorta Heartbeat is a peristaltic wave Heartbeat is a peristaltic wave Accessory pulsatile organs help move hemolymph into wings and legs Accessory pulsatile organs help move hemolymph into wings and legs Hemolymph composed of plasma and amebocytes but does not function in oxygen transport in most insects Hemolymph composed of plasma and amebocytes but does not function in oxygen transport in most insects In some insects, particularly aquatic immature in low oxygen environments In some insects, particularly aquatic immature in low oxygen environments Hemoglobin is present and functions in oxygen transport Hemoglobin is present and functions in oxygen transport Class Insecta

41. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-41 Gas Exchange Gas Exchange Terrestrial animals are faced with the dilemma of exchanging gases while preventing water loss Terrestrial animals are faced with the dilemma of exchanging gases while preventing water loss Tracheal system Tracheal system Network of thin-walled tubes that branch throughout the insect body Network of thin-walled tubes that branch throughout the insect body Evolved independently of that of other arthropod groups Evolved independently of that of other arthropod groups Spiracles open to the tracheal trunks Spiracles open to the tracheal trunks 2 spiracles on thorax and 7–8 on abdomen 2 spiracles on thorax and 7–8 on abdomen Valve on the spiracle Valve on the spiracle Reduces on water loss and may serve as a dust filter Reduces on water loss and may serve as a dust filter Class Insecta

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43. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-43 Tracheae are composed of a single layer of cells lined with cuticle that is shed at each molt Tracheae are composed of a single layer of cells lined with cuticle that is shed at each molt Spiral thickenings of cuticle, called taenidia, prevent the tracheae from collapsing Spiral thickenings of cuticle, called taenidia, prevent the tracheae from collapsing Tracheae branch out into fluid-filled tubules called tracheoles that reach individual body cells Tracheae branch out into fluid-filled tubules called tracheoles that reach individual body cells System provides gas transport without use of oxygen-carrying pigments System provides gas transport without use of oxygen-carrying pigments Diving beetles use abdominal hairs to maintain a bubble under wings, an “artificial gill” Diving beetles use abdominal hairs to maintain a bubble under wings, an “artificial gill” Mosquito larvae use short breathing tubes to snorkel surface air Mosquito larvae use short breathing tubes to snorkel surface air Class Insecta

44. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-44 Air sacs in insects are dilated tracheae without taenidia Air sacs in insects are dilated tracheae without taenidia Contraction of muscles in the jaw or limbs causes increased pressure inside the exoskeleton Contraction of muscles in the jaw or limbs causes increased pressure inside the exoskeleton Elevated pressure causes contraction of tracheae for exhalation Elevated pressure causes contraction of tracheae for exhalation Muscular movements may assist in moving air in and out of air sacs Muscular movements may assist in moving air in and out of air sacs Very small insects Very small insects Transport gases by simple diffusion Transport gases by simple diffusion Aquatic insect nymphs Aquatic insect nymphs May use tracheal gills or rectal gills May use tracheal gills or rectal gills Class Insecta

45. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-45 Excretion and Water Balance Excretion and Water Balance Insects and spiders utilize Malpighian tubules in conjunction with rectal glands Insects and spiders utilize Malpighian tubules in conjunction with rectal glands Malpighian tubules vary in number but join between the midgut and hindgut Malpighian tubules vary in number but join between the midgut and hindgut Blind ends of tubules float freely in hemocoel bathed in hemolymph Blind ends of tubules float freely in hemocoel bathed in hemolymph Potassium is actively secreted into the tubules Potassium is actively secreted into the tubules Other solutes follow gradient Other solutes follow gradient Main waste product is uric acid Main waste product is uric acid Flows across at upper end that is mildly alkaline Flows across at upper end that is mildly alkaline In the lower end of the tubule In the lower end of the tubule Potassium combines with CO 2 and is reabsorbed Potassium combines with CO 2 and is reabsorbed Rectal glands reabsorb chloride, sodium and water Rectal glands reabsorb chloride, sodium and water Wastes pass out of body Wastes pass out of body Class Insecta

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47. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-47 Nervous System Nervous System Resemble that of larger crustaceans, with fusion of ganglia Resemble that of larger crustaceans, with fusion of ganglia Some have a giant fiber system Some have a giant fiber system A stomadeal system corresponds to the autonomic system of vertebrates A stomadeal system corresponds to the autonomic system of vertebrates Neurosecretory cells in brain function to control molting and metamorphosis Neurosecretory cells in brain function to control molting and metamorphosis Class Insecta

48. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-48 Sense Organs Sense Organs Many insects have keen sensory perception Many insects have keen sensory perception Most sense organs are microscopic and located in body wall Most sense organs are microscopic and located in body wall Different organs respond to mechanical, auditory, chemical, visual, and other stimuli Different organs respond to mechanical, auditory, chemical, visual, and other stimuli Mechanoreception Mechanoreception Touch, pressure, vibration, etc. are detected by sensilla Touch, pressure, vibration, etc. are detected by sensilla May be a single hair-like seta or a complex organ May be a single hair-like seta or a complex organ Distributed widely over antennae, legs, and body Distributed widely over antennae, legs, and body Class Insecta

49. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-49 Auditory Reception Auditory Reception Sensitive setae (hair sensilla) or tympanal organs detect airborne sounds Sensitive setae (hair sensilla) or tympanal organs detect airborne sounds Tympanal organs occur in Orthoptera, Hemiptera and Lepidoptera Tympanal organs occur in Orthoptera, Hemiptera and Lepidoptera Organs in legs can detect vibrations of substrate Organs in legs can detect vibrations of substrate Class Insecta

50. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-50 Chemoreception Chemoreception Usually bundles of sensory cell processes located in sensory pits Usually bundles of sensory cell processes located in sensory pits May occur on mouthparts, antennae, and legs May occur on mouthparts, antennae, and legs Some insects can detect odors several kilometers away Some insects can detect odors several kilometers away Feeding, mating, habitat selection, and host- parasite relationships are mediated through chemical senses Feeding, mating, habitat selection, and host- parasite relationships are mediated through chemical senses Class Insecta

51. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-51 Visual Reception Visual Reception 2 types of eyes: simple and compound 2 types of eyes: simple and compound Honeybee studies indicate that ocelli monitor light intensity but do not form images Honeybee studies indicate that ocelli monitor light intensity but do not form images Compound eyes may contain thousands of ommatidia Compound eyes may contain thousands of ommatidia Ommatidia structure similar to that of crustaceans Ommatidia structure similar to that of crustaceans Insects can see simultaneously in almost all directions Insects can see simultaneously in almost all directions Image is myopic and fuzzy Image is myopic and fuzzy Class Insecta

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53. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-53 Flying insects have a higher flicker-fusion rate Flying insects have a higher flicker-fusion rate Distinguish 200–300 flashes per second Distinguish 200–300 flashes per second A bee can distinguish ultraviolet light but cannot detect shades of red A bee can distinguish ultraviolet light but cannot detect shades of red Class Insecta

54. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-54 Other Senses Other Senses Insects are very sensitive to temperature, especially cells in antennae and legs Insects are very sensitive to temperature, especially cells in antennae and legs Insects also detect humidity, proprioception, gravity, and other physical properties Insects also detect humidity, proprioception, gravity, and other physical properties Class Insecta

55. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-55 Neuromuscular Coordination Neuromuscular Coordination Active insects require excellent neuromuscular coordination Active insects require excellent neuromuscular coordination Arthropod muscles are cross-striated Arthropod muscles are cross-striated Strength of muscle is related to its cross- sectional area Strength of muscle is related to its cross- sectional area A flea can jump 100 times its length by storing energy in an elastic resilin protein A flea can jump 100 times its length by storing energy in an elastic resilin protein Class Insecta

56. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-56 Reproduction Reproduction Parthenogenesis occurs predominantly in some Hemiptera and Hymenoptera Parthenogenesis occurs predominantly in some Hemiptera and Hymenoptera Sexual reproduction is the norm Sexual reproduction is the norm Sexes are separate Sexes are separate Sexual Attraction Sexual Attraction Female moths secrete a pheromone to attract males from a great distance Female moths secrete a pheromone to attract males from a great distance Fireflies use flashes of light to detect mates Fireflies use flashes of light to detect mates Some insects use sounds, color signals, and other courtship behaviors Some insects use sounds, color signals, and other courtship behaviors Class Insecta

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58. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-58 Fertilization usually internal Fertilization usually internal Sperm may be released directly or packaged into spermatophores Sperm may be released directly or packaged into spermatophores Spermatophores are result of an evolutionary transition from marine to terrestrial existence Spermatophores are result of an evolutionary transition from marine to terrestrial existence May be transferred both without copulation and during copulation. May be transferred both without copulation and during copulation. Female may only mate once and store sperm to fertilize eggs throughout her life 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 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 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 Wasps may have to locate a specific species that is the only host to their young Class Insecta

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61. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-61 Metamorphosis and Growth Metamorphosis and Growth Various forms of metamorphosis produce degrees of change among different insect groups Various forms of metamorphosis produce degrees of change among different insect groups Most insects change form after hatching from egg Most insects change form after hatching from egg Each stage between molts is called an instar Each stage between molts is called an instar Insects develop wings during the last stage Insects develop wings during the last stage Class Insecta

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65. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-65 Ametabolous (Direct) Development Ametabolous (Direct) Development Silverfish and springtails have young similar to adults except in size and sexual maturation Silverfish and springtails have young similar to adults except in size and sexual maturation Stages are egg-juveniles-adult Stages are egg-juveniles-adult Wingless insects Wingless insects Class Insecta

66. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-66 Hemimetabolous Metamorphosis Hemimetabolous Metamorphosis Some insects undergo a gradual metamorphosis Some insects undergo a gradual metamorphosis Grasshoppers, cicadas, mantids, true bugs, mayflies and dragonflies exhibit this metamorphosis Grasshoppers, cicadas, mantids, true bugs, mayflies and dragonflies exhibit this metamorphosis Young are called nymphs Young are called nymphs Bud-like growths in early instars show where the adult wings will eventually develop Bud-like growths in early instars show where the adult wings will eventually develop Stages are egg-nymph-adult Stages are egg-nymph-adult Class Insecta

67. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-67 Holometabolous Metamorphosis Holometabolous Metamorphosis About 88% of insects undergo complete metamorphosis About 88% of insects undergo complete metamorphosis Separates the physiology of larval growth, pupal differentiation, and adult reproduction Separates the physiology of larval growth, pupal differentiation, and adult reproduction Larvae and adults often live in completely different environments Larvae and adults often live in completely different environments No competition No competition After several larval instars After several larval instars Larval moth or butterfly becomes a pupa inside a cocoon or chrysalis Larval moth or butterfly becomes a pupa inside a cocoon or chrysalis Pupae often pass the winter in this stage Pupae often pass the winter in this stage Final molt occurs and the adult emerges in spring Final molt occurs and the adult emerges in spring Stages are egg-larva-pupa-adult Stages are egg-larva-pupa-adult Class Insecta

68. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-68 Physiology of Metamorphosis Physiology of Metamorphosis Hormones regulate insect metamorphosis Hormones regulate insect metamorphosis Brain and nerve cord ganglia produce brain hormone or ecdysiotropin Brain and nerve cord ganglia produce brain hormone or ecdysiotropin Neurosecretory cells send axons to the corpora cardiaca that stores and ultimately releases these hormones Neurosecretory cells send axons to the corpora cardiaca that stores and ultimately releases these hormones Brain hormone circulates in the hemolymph to the prothoracic gland in the head or prothorax Brain hormone circulates in the hemolymph to the prothoracic gland in the head or prothorax Prothoracic gland produces molting hormone or ecdysone in response Prothoracic gland produces molting hormone or ecdysone in response Ecdysone starts the molting process Ecdysone starts the molting process Class Insecta

69. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-69 Corpora allata produces juvenile hormone Corpora allata produces juvenile hormone Molting continues as long as juvenile hormone (neotenine) is sufficiently present Molting continues as long as juvenile hormone (neotenine) is sufficiently present In later instars, the corpora allata releases less juvenile hormone In later instars, the corpora allata releases less juvenile hormone When juvenile hormone reaches a low level, the larva molts to become a pupa When juvenile hormone reaches a low level, the larva molts to become a pupa Cessation of juvenile hormone production in the pupa leads to an adult at the last molt Cessation of juvenile hormone production in the pupa leads to an adult at the last molt In hemimetabolous insects, cessation of juvenile hormone occurs in the last nymphal instar In hemimetabolous insects, cessation of juvenile hormone occurs in the last nymphal instar In adults, the corpora allata becomes active again in normal egg production In adults, the corpora allata becomes active again in normal egg production The prothoracic glands degenerate in adult insects and adults do not molt The prothoracic glands degenerate in adult insects and adults do not molt Class Insecta

70. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-70 Diapause Diapause Period of dormancy in the annual life cycle that is independent of conditions Period of dormancy in the annual life cycle that is independent of conditions Winter dormancy: hibernation Winter dormancy: hibernation Summer dormancy: estivation Summer dormancy: estivation Any stage (eggs, larvae, pupae, or adults) may remain dormant to survive adverse conditions Any stage (eggs, larvae, pupae, or adults) may remain dormant to survive adverse conditions Internally controlled but may be triggered by environmental cues such as day length Internally controlled but may be triggered by environmental cues such as day length Always occurs at end of an active growth stage Always occurs at end of an active growth stage Insect is then ready for another molt Insect is then ready for another molt Many larvae do not develop beyond this point until spring in spite of mild temperatures Many larvae do not develop beyond this point until spring in spite of mild temperatures Class Insecta

71. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-71 Defense Defense Protective coloration, warning coloration, and mimicry are protective adaptations Protective coloration, warning coloration, and mimicry are protective adaptations Stink bugs and others have repulsive odors and tastes Stink bugs and others have repulsive odors and tastes Some insects are aggressive (e.g., bees and ants) Some insects are aggressive (e.g., bees and ants) The monarch caterpillar incorporates a poisonous substance from its food plant, milkweed The monarch caterpillar incorporates a poisonous substance from its food plant, milkweed The bombardier beetle can spray an attacking enemy with irritating chemicals The bombardier beetle can spray an attacking enemy with irritating chemicals Class Insecta

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73. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-73

74. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-74 Behavior and Communication Behavior and Communication Insects respond to many environmental stimuli Insects respond to many environmental stimuli Responses are governed by both physiological state of the animal and its nerve pathways Responses are governed by both physiological state of the animal and its nerve pathways Many behaviors are complex sequences of responses Many behaviors are complex sequences of responses Most behavior is innate but some involve simple learning Most behavior is innate but some involve simple learning Class Insecta

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76. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-76 Pheromones Pheromones Chemicals secreted by one individual to affect the behavior of another individual Chemicals secreted by one individual to affect the behavior of another individual Attract the opposite sex, trigger aggregation, fend off aggression, and mark trails 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 Bees, wasps, and ants can recognize nestmates and signal an alarm if strangers enter the nest Can be used to trap insects to monitor populations Can be used to trap insects to monitor populations Class Insecta

77. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-77 Sound Production and Reception Sound Production and Reception Sounds are used as warning devices, advertisement of territory, and courtship songs. Sounds are used as warning devices, advertisement of territory, and courtship songs. Crickets chirp for courtship and aggression Crickets chirp for courtship and aggression Male cicada vibrates paired membranes on abdomen to attract females Male cicada vibrates paired membranes on abdomen to attract females Tactile Communication Tactile Communication Involves tapping, stroking, grasping, and antennae touching Involves tapping, stroking, grasping, and antennae touching Some beetles, flies and springtails use bioluminescence Some beetles, flies and springtails use bioluminescence Some female fireflies mimic another species’ flash pattern to attract males and then eat them Some female fireflies mimic another species’ flash pattern to attract males and then eat them Class Insecta

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79. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-79 Social Behavior Social Behavior Some social communities are temporary and uncoordinated Some social communities are temporary and uncoordinated Others are highly organized and depend on chemical and tactile communication Others are highly organized and depend on chemical and tactile communication Caste differentiation is common in most organized social groups Caste differentiation is common in most organized social groups Class Insecta

80. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-80 Honeybees Have a few male drones, a fertile female queen and many female workers Have a few male drones, a fertile female queen and many female workers Drones develop by parthenogenesis Drones develop by parthenogenesis Development of a fertile queen requires ingestion of “royal jelly” Development of a fertile queen requires ingestion of “royal jelly” Queen secretes “queen substance” to prevent workers from maturing or feeding larvae royal jelly Queen secretes “queen substance” to prevent workers from maturing or feeding larvae royal jelly A honeybee hive may contain 60,000–70,000 individuals A honeybee hive may contain 60,000–70,000 individuals Scouts inform workers on location of food Scouts inform workers on location of food Class Insecta

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82. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-82 Termites Fertile king and queen fly away to start a new colony Fertile king and queen fly away to start a new colony Mate and lose wings Mate and lose wings Immature members are wingless and become workers and soldiers Immature members are wingless and become workers and soldiers Soldiers have large heads and defend colony Soldiers have large heads and defend colony Reproductive individuals secrete inhibiting pheromones that produce sterile workers Reproductive individuals secrete inhibiting pheromones that produce sterile workers Nymphs feed from each other in trophallaxis, thus spreading the pheromone about Nymphs feed from each other in trophallaxis, thus spreading the pheromone about Class Insecta

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84. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-84 Worker castes also produce worker and soldier substances Worker castes also produce worker and soldier substances Drops in these pheromone levels result in more of the needed caste developing in the next generation Drops in these pheromone levels result in more of the needed caste developing in the next generation Class Insecta

85. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-85 Ants Differ from termites Differ from termites Ants are darker, hard-bodied, and have thread-like waist Ants are darker, hard-bodied, and have thread-like waist In ant colonies, the male ant dies after mating In ant colonies, the male ant dies after mating Ants have wingless soldiers and workers, and often have variations of these castes Ants have wingless soldiers and workers, and often have variations of these castes Ants have also evolved striking patterns of “economic” behavior: making slaves, fungus farming, sewing nests together, tool use, and herding Ants have also evolved striking patterns of “economic” behavior: making slaves, fungus farming, sewing nests together, tool use, and herding Class Insecta

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87. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-87 Insects and Human Welfare Beneficial Insects Beneficial Insects Insects produce honey, beeswax, silk and shellac Insects produce honey, beeswax, silk and shellac Of more economic importance, bees pollinate $10 billion worth of food crops in the U.S. annually Of more economic importance, bees pollinate $10 billion worth of food crops in the U.S. annually Pollinating insects and flowering plants are tightly co-evolved Pollinating insects and flowering plants are tightly co-evolved Predaceous and parasitoid insects are vital in controlling many pest insect populations Predaceous and parasitoid insects are vital in controlling many pest insect populations

88. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-88 Dead animals rapidly consumed by fly maggots Dead animals rapidly consumed by fly maggots Insects are critical components of most food chains and an important food source for many fish and birds Insects are critical components of most food chains and an important food source for many fish and birds Insects and Human Welfare

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90. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-90 Harmful Insects Harmful Insects Harmful insects eat and destroy plants and fruits Harmful insects eat and destroy plants and fruits Nearly every cultivated crop has several insect pests Nearly every cultivated crop has several insect pests Requires substantial money for insect control Requires substantial money for insect control Bark beetles, spruce budworms, the gypsy moth and others are serious forest pests. Bark beetles, spruce budworms, the gypsy moth and others are serious forest pests. Insects also destroy food, clothing, and property Insects also destroy food, clothing, and property Insects and Human Welfare

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92. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-92 Medically important insects include vectors for disease agents Medically important insects include vectors for disease agents 10% of all arthropod species are parasites or “micropredators” 10% of all arthropod species are parasites or “micropredators” Warble and bot flies attack humans and domestic livestock Warble and bot flies attack humans and domestic livestock Malaria is carried by Anopheles mosquitos Malaria is carried by Anopheles mosquitos Most common major world disease Most common major world disease Yellow fever and lymphatic filariasis are also mosquito-borne Yellow fever and lymphatic filariasis are also mosquito-borne Insects and Human Welfare

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94. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-94 Fleas carry plague, a disease that changed human history in the Middle Ages Fleas carry plague, a disease that changed human history in the Middle Ages Lice carry typhus fever Lice carry typhus fever The tsetse fly carries African sleeping sickness The tsetse fly carries African sleeping sickness The newest viral plague to hit North America, the West Nile virus, is carried by mosquitos The newest viral plague to hit North America, the West Nile virus, is carried by mosquitos Insects and Human Welfare

95. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-95 Control of Insects Control of Insects Broad-spectrum insecticides damage beneficial insect populations along with targeted pest Broad-spectrum insecticides damage beneficial insect populations along with targeted pest Some chemical pesticides persist in the environment and accumulate as they move up the food chain Some chemical pesticides persist in the environment and accumulate as they move up the food chain Some strains of insects have evolved a resistance to common insecticides Some strains of insects have evolved a resistance to common insecticides Biological control Biological control Use of natural agents, including diseases, to suppress an insect population Use of natural agents, including diseases, to suppress an insect population Insects and Human Welfare

96. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-96 Bacillus thuringiensis Bacillus thuringiensis Bacterium that controls lepidopteran pests Bacterium that controls lepidopteran pests Gene coding for the “B.t.” toxin has been introduced to other bacteria and transferred to crop plants Gene coding for the “B.t.” toxin has been introduced to other bacteria and transferred to crop plants Some viruses and fungi may be economical pesticides Some viruses and fungi may be economical pesticides Natural predators or parasites of insect pests can be raised and released to control pest Natural predators or parasites of insect pests can be raised and released to control pest Release of sterile males can eradicate the few insect species that only mate once Release of sterile males can eradicate the few insect species that only mate once Insects and Human Welfare

97. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-97 Insects and Human Welfare Pheromones can monitor pests and hormones may play a role in disrupting the life cycle Pheromones can monitor pests and hormones may play a role in disrupting the life cycle Integrated pest management Integrated pest management Combined use of all possible, practical techniques listed above, to reduce reliance on chemical insecticides Combined use of all possible, practical techniques listed above, to reduce reliance on chemical insecticides

98. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-98 Phylogeny and Adaptive Diversification Phylogeny Phylogeny Understanding of the relationships among arthropods has changed over the past decade Understanding of the relationships among arthropods has changed over the past decade Using molecular data, members of former subphylum Uniramia are now divided between subphylum Myriapoda and Hexapoda Using molecular data, members of former subphylum Uniramia are now divided between subphylum Myriapoda and Hexapoda The nature of the relationship, however, between hexapods and crustaceans is not well understood The nature of the relationship, however, between hexapods and crustaceans is not well understood

99. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-99 Some phylogenies support a sister-taxon relationship between them, but others indicate that hexapods arose within Crustacea Some phylogenies support a sister-taxon relationship between them, but others indicate that hexapods arose within Crustacea Future studies may show that subphylum Crustacea is paraphyletic Future studies may show that subphylum Crustacea is paraphyletic Phylogenies that support hexapods arising from within Crustacea, find that hexapods are most similar to brachiopod, cephaplocarid, and remipedian crustaceans Phylogenies that support hexapods arising from within Crustacea, find that hexapods are most similar to brachiopod, cephaplocarid, and remipedian crustaceans Phylogeny and Adaptive Diversification

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101. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-101 Within Hexapoda, Entognatha is the sister taxon to class Insecta Within Hexapoda, Entognatha is the sister taxon to class Insecta However, some research indicates that entognathous mouthparts may have evolved several times and that some entognathans are closer to insects than to other entognathans However, some research indicates that entognathous mouthparts may have evolved several times and that some entognathans are closer to insects than to other entognathans Phylogeny and Adaptive Diversification

102. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-102 Adaptive Diversification Adaptive Diversification The first terrestrial arthropods were scorpions and millipedes that appeared in the Silurian period The first terrestrial arthropods were scorpions and millipedes that appeared in the Silurian period The ancestral insect had a head and trunk of similar somites The ancestral insect had a head and trunk of similar somites Insects have specialized the first three post-cephalic somites as thorax and lost the remaining appendages Insects have specialized the first three post-cephalic somites as thorax and lost the remaining appendages Some modern apterygote orders have abdominal styli that are considered vestigial legs Some modern apterygote orders have abdominal styli that are considered vestigial legs Phylogeny and Adaptive Diversification

103. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-103 Recent fossil evidence suggests winged insects were in existence about 400 million years ago Recent fossil evidence suggests winged insects were in existence about 400 million years ago Ancestral flying insects may have derived from aquatic insects or insects with aquatic juveniles; the external gills on their thorax may be the derivative of wings Ancestral flying insects may have derived from aquatic insects or insects with aquatic juveniles; the external gills on their thorax may be the derivative of wings Metamorphosis also distinguished insects by the Permian period Metamorphosis also distinguished insects by the Permian period Phylogeny and Adaptive Diversification

104. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 21-104 Hemimetabolous metamorphosis, chewing mouthparts and cerci group the Orthoptera, Dermaptera, Isoptera and Embioptera Hemimetabolous metamorphosis, chewing mouthparts and cerci group the Orthoptera, Dermaptera, Isoptera and Embioptera Hemimetabolous metamorphosis and sucking mouthparts group the Thysanoptera, Hemiptera, Homoptera and perhaps the Psocoptera, Zoraptera, Mallophaga and Anoplura Hemimetabolous metamorphosis and sucking mouthparts group the Thysanoptera, Hemiptera, Homoptera and perhaps the Psocoptera, Zoraptera, Mallophaga and Anoplura Other orders have holometabolous metamorphosis and are the most specialized Other orders have holometabolous metamorphosis and are the most specialized Phylogeny and Adaptive Diversification