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)