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 Function
1. 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 crosssectional 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 Humans
1 & 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)