Terrestrial Mandibulates Chapter 20. I. Characteristics of Subphylum Uniramia Body tagmata: head,...
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Transcript of Terrestrial Mandibulates Chapter 20. I. Characteristics of Subphylum Uniramia Body tagmata: head,...
Terrestrial Mandibulates
Chapter 20
I. Characteristics of Subphylum Uniramia
Body tagmata: head, thorax, abdomen
1 pair of antenna; appendages uniramous
Primarily terrestrial
II. Class Chilopoda A. Characteristics
Found under logs, bark, and stones
Carnivorous, eating earthworms, cockroaches, and other insects
House centipede has 15 pairs of long legs
Most are harmless but some tropical ones are dangerous
B. Body Structure
Flattened bodies with up to 177 somites 1st body segment has poisonous claws Head: 1 pair antennae, 1 pair mandibles,
1-2 pairs maxillae Eyes on sides of head are groups of ocelli Separate sexes Some lay eggs; some viviparous Young resemble small adults
III. Class Diplopoda A. Characteristics
Less active than centipedes
Eat decayed plants; a few eat living plants
Slow moving; roll into a coil for defense
Some secrete toxic or repellant substances from special glands on side of body
B. Body Structure
2 pairs of legs per somite
Bodies have 25-100 somites
Head: 2 clusters of simples eyes, 1 pair of antennae, mandibles, and maxillae
Female lays eggs in nest and guards them
Larvae have only 1 pair of legs per somite
IV. Class Insecta A. Diversity
Most diverse and abundant of all arthropods
Estimated at 1 million species
Found in nearly all habitats except sea
Most animals and plants have insect parasites externally and internally
Range in size from 1 mm to 20 cm; tropical insects tend to be larger
B. Adaptability
Flight and small size makes insects widely distributed
Well-protected eggs can withstand rigorous conditions and are easily dispersed
Structural and behavioral adaptations give them access to many possible niches
Some insects are adapted to coexist with one plant species
Exoskeletons allows for desert survival
C. External Form & Function 1. Head
1 pair of large compound eyes
1 pair of antennae; vary greatly in form; feel, taste, and hear
Mouthparts: labrum, pair of mandibles and maxillae, a labium, an a hypopharynx
Insect Heads
2. Thorax
Prothorax, mesothorax, metathorax; each has a pair of legs
Mesothorax and metathorax each have wings
Wings have double membrane with veins (strengthens and identifies insects)
Legs end in terminal pads and claws
Some legs are modified for special purposes: hindlegs of grasshopper for jumping; forelegs of preying mantis for grasping prey; honeybee legs for collecting pollen
Insect Legs
3. Abdomen
9-11 segments ending in a pair of cerci Larval or nymph forms may have appendages
not in adults External genitalia at end of abdomen
D. Flight 1. Wings
Outgrowth of cuticle from meso- and metathoracic segments
Diptera (flies) have only one pair; rest have 2; flies have halteres (knobby reduced wings) that provide balance
Lice, fleas, and nonreproductive ants and termites are wingless
Wings for flight are thin and membranous; thick horny front ones of beetle are protective; butterflies have scales on wings
Insect Wings
2. Muscles
Direct flight muscles attach to wing Indirect flight muscle changes shape of
thorax which then moves wings Dragonflies and cockroaches use direct
muscles to fly Bees, wasps, and flies move indirect
muscles Beetles and grasshoppers use combination Wings move in figure-8 Wing beats vary from 4/second
(butterflies) to over 1000/second (midges)
E. Internal Form and Function1. Digestive System
Mouth seizes and crushes food; salivary glands to aid in digestion; some insects have sucking mouthparts; flies have lobes that absorb food
Gizzard grinds food; midgut digests and absorbs food; hindgut absorbs water
Most insects feed on plant tissue or juices Some ants and termites cultivate fungus
gardens Some insects are predators or are parasites
(hyperparasites parasitize parasitic insects)
2. Circulatory System
Tubular heart moves hemolymph through dorsal aorta
Heartbeat peristalic wave
Accessory organs move hemolymph into wings and legs
Hemolymph has plasma and amebocytes but does not use oxygen transport
3. Respiratory System
Tracheal system a network of thin tubes branched throughout insects body
Spiracles open to trachea; 2 on thorax and 7-8 on abdomen
Valve on spiracle prevents water loss and acts as dust filter
Tracheae branch into fluid filled tracheoles that reach individual body cells allowing gas exchange
4. Excretion
Malpighian tubules excrete uric acid Rectal glands reabsorb chloride, sodium,
and water allowing other wastes to be excreted
5. Nervous System
Fused ganglia Neurosecretory cells in brain control
molting and metamorphosis
6. Sense Organs a. Mechanoreception
Touch, pressure, and vibration are picked up by sensilla ( single hair-like seta or organ)
Sensilla on antennae, legs, and body
b. Auditory Reception
Sensilla or tympanal organs may detect airbourne sounds
Organs found on Orthoptera, Homoptera, and Lepidoptera
Organs in legs can detect vibrations on ground
C. Visual Reception
Ocelli monitor light intensity but do not form images
Compound eyes have ommatidia like crustaceans
See simultaneously in almost all directions; image is myopic and fuzzy
Flying insects can process 200-300 image flashes per second
Bees use UV light but can not see red
D. Chemoreception & Other Senses
Sensory cells located in sensory pits located on mouthparts, antennae, and legs
Can detect some odors kilometers away
Feeding, mating, habitat selection, host selection all done though use of chemoreceptors
Cells on legs and antennae detect temperature changes, humidity, and gravity
7. Muscular System
Muscles are cross-striated Strength of muscle is related to cross-
sectional area
F. Reproduction
Sexes are separate Some insects use
phermones, light, sound, color signals, courtship behaviors as attractant
Sperm deposited in vagina during fertilization
May lay a few eggs and care for young or lay many eggs
Eggs laid on host plant or animal
G. Metamorphosis and Growth
Most insects change form after hatching from egg
Each stage between molts is called an instar
Wings develop during last stage when useful during reproduction
1. Homometabolous
88% of insects Egg, larval growth
(may have several instars), pupal differentiation, adult reproduction
Pupa usually formed over winter, adult emerging in spring
2. Hemimetabolous
Gradual metamorphosis
Grasshoppers, cicadas, mantids, true bugs, mayflies, dragonflies
Young are called nymphs
Egg, nymph, adult
3. Direct Development
Young similar to adults just smaller in size
Silverfish and springtails, primarily wingless insects
Egg, juvenile, adult
4. Physiology of Metamorphosis
Regulated by hormones produced by brain and ganglia
Molting hormone produced in response Molting continues as long as juvenile
hormone produced With each instar, less and less juvenile
hormone produced, until 0 is produced and adult emerges
Adults do not molt
H. Diapause
Period of dormancy in life cycle independent of conditions; genetically determined but may be triggered by environmental cues
Usually active growth triggers diapause Winter dormancy—hibernation Summer dormancy—estivation Any life stage may become dormant to
survive adverse conditions
I. Defense
Protective coloration, warning coloration, mimicry are protective adaptations
Also repulsive odors and tastes (stink bugs) or may spray irritating chemicals (bombardier beetle)
Some are aggressive (bees and ants)
J. Behavior and Communication
Well developed senses lead insects to respond to many stimuli
Most behavior is innate but some is learned
1. Phermones
Chemicals secreted by one individual to affect behavior of another individual
Attract opposite sex, trigger swarming, fend off aggression, and mark trails
Bees, wasps, ants recognize nestmates and trigger alarms in response to invaders
Phermones used to attract and trap insects
2. Sound Production & Reception
Sounds used as warnings, announcing territory, and courtship songs
Sounds may be made by chirps or rubbing of body parts
3. Tactile Communication
Tapping, rubbing, grasping, and antennae touching
Bioluminescence
4. Social Behavior
True societies as demonstrated by bees, termites, and ants have developed a complex social life as a means to perpetuate their species.
The societies exhibit a caste system which involves all stages in the life cycle, involve complex communication, and division of labor.
Honey bees have 3 castes: queen (single sexually mature female), drones (few hundred sexually mature males), and workers (thousands of sexually inactive females).
Termites and ants have several fertile males (kings) and females (queens); sterile individuals are workers and soldiers. Soldiers have larger heads and mandibles for defense.
Paper Wasps
Honey Bee Waggle Dance
Queen ant and male
K. Insects and Humans1 & 2 Beneficial/Harmful Insects
Insects produce products that humans utilize like honey, beeswax, silk, shellac
Insects also pollinate $10 billion dollars worth of human food crops in the US.
Some insects prey on other insects humans consider pests.
Some insects are agricultural/horticultural pests
Other insects transmit diseases, parasitize humans, or destroy property.
3. Control of Insects
Insect play an important role in the food web since they are food sources for many organisms and their removal would have a cataclysmic effect.
Control of insects through insecticides has a lasting effect on the environment since many insecticides accumulate in the body tissues of larger organisms, eventually harming them as well.
Biological controls utilize other predatory insects, toxic strains of bacteria or viruses, engineering plants with toxins, releasing sterile males, or altering reproduction rates through the use of hormones.
Orthoptera (grasshoppers, crickets, katydids, and cockroaches)
Isoptera (termites) Dermaptera (earwigs) Anoplura (sucking lice) Hemiptera (
"true" bugs) Homoptera (aphids,
mealy bugs, and cicadas)
Ephemeroptera (mayflies)
Odonata (dragonflies and damselflies)
Neuroptera (dobsonflies and lacewings)
Coleoptera (weevils, ladybugs, and beetles)
Lepidoptera (butterflies and moths)
Diptera (mosquitoes, flies, and gnats)
Siphonaptera (fleas) Hymenoptera (bees,
wasps, and ants)