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Insects and Human Society

Insects and Human Society

Lecture 3: Insect Anatomy

External Morphologyp gy

Insects are heterotrophic invertebrates w/ an articulated exoskeleton and 6-legged adults

Living organismsLiving organisms

Kingdom: Animalia

Ph l A th dPhylum: Arthropoda

Class: Insecta

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External AnatomyStudy of external anatomy is called Morphology

Morphology is coined by Goethe in 1822 from the Greek world Morphē (= Form) and the German world Logie (= study)

Morphology is the branch of biology that deals with form and structure of animals and plants

External anatomy is important to 1) understand the functions of the various insect designs and to 2) allow identification of insects and their relatives

Objectives of Lecture

Describe and discuss the functions of diff t b d t f i tdifferent body parts of insects:

CuticleBody segmentationStructure of head, thorax,

abdomen and their appendages

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The cuticleProvides the strong exoskeleton of body (that serve to give rigid structure & protect i l ) d h d (i linternal organs) and the apodemes (internal support and attachment point for muscles)Cuticle may range from rigid and armor-like (adult beetles) to thin and flexible (many larvae)larvae)Prevention of water loss (desiccation) is a critical function of the cuticleKey contributor of the success of insect

The cuticleCuticle is a thin layer but a complex structure

Epidermis: Single layer that lies beneath and t th ti lsecretes the cuticle

Cuticle is composed of the thicker procuticleoverlaid with thin epicuticleEpidermis and cuticle together form an

integument (or body wall) which is the outerintegument (or body wall) which is the outer covering of living tissues of an insect In between sclerites the body wall is softer –

allows for growth, expansion and movement

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The Body WallThe body wall or integument is composed of a layer of cells called the epidermis, with the basement membrane on the inside and the cuticlebasement membrane on the inside and the cuticleon the outside

Procuticle

The body wall-cuticle• The epicuticle (top layer) prevents water loss,

repels excessive water, deters predation, provides patterns for mimicry, reflect solar

• The exocuticle gives the cuticle its strength and resilience and is formed from chitin (also base for wood, hair, horns)

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The body wall-PigmentsBrown and black pigments called melanin are present in cuticle to give insect colorother colors may be possible by other pigmentsother colors may be possible by other pigments with clear cuticle or diffraction patterns in cuticle to give iridescence

Some basic terminology

FrontRear

Top

Bottom

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Segmentation and TagmosisArthropod body is composed of several segments Primitive insects were worm-like with many segments (generall 20)segments (generally 20) In today’s insects, segments are grouped into function units or regions or tagmata -- this process is called TagmosisThe 20 original segments composing insects are grouped into 3 regions:

Head (6 segments)Thorax (3 segments)Abdomen (11 segments)

• Insect: Derived from the Latin word “insecticum” meaning ‘cut into’• Insect body is cut into three parts: Head (H) Thorax (T) & Abdomen (A)(H), Thorax (T) & Abdomen (A)

A T H

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Primary Functions of Tagmata

HeadSensory perceptionNeural integrationFood gathering and manipulation

ThoraxLocomotionLocomotion

AbdomenHouses visceral organs (Digestion, Reproduction, etc…)

Insect HeadStructure

Head is entirely encased in rigid exoskeleton No sign of segmentationA t i t f th h d i th fAnterior part of the head is the frons

OrientationBased on the inclination of the long axis of the head compared to the entire body, there are 3 basic types of orientationPrognathus: long axis of head horizontal and in line w/ long

axis of insect body

Hypognathus: long axis of head is at right angle (vertical) to the long axis of insect bodyOpisthognathus: long axis of head horizontal, but the tip

end is directed backward and arises between the anterior legs

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Insect Head• Composed of the cranum, insect head bears eyes

(compound eyes and ocelli), antennae and mouthparts

Ep

AntennaeEyes

Frons

Mouthparts

Insect Head -- Eyes (Insect Vision)Compound Eyes

Compound eyes are large and well developed w/ many small individual facets or ommatidia (ommatidium in singular); has

lli l d li h i llcrystalline lens and light concentrating cellsForm a picture of what insects see (light sensitive)Present in most adult insects but absent from larvae

Ocelli (Ocellus)Simple eyes lack crystalline lens3 light-sensitive eyes, typically arranged in a triangle are located in the dark surface on the face of the insect

Stemmata (only present on some species)Simple eyes with crystalline lens located laterally on certain larvae (holometabolous)

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Insect Head -- Eyes (Insect Vision)Compound Eyes

Insects cannot move or focus their eyes; they have a sharp vision for only a short distance (less than 1 yard)they can see a broader range of light rays than peopleInsects have no eye lid, their eyes are always open

OcelliSimple eyes cannot form imagescan only tell differences between dark and light

A fly has huge compound eyes that cover most of its head

Insect Head -- AntennaeOne pair of antennae

Most insects have 2 antennae between their eyesThese antennae are jointed and mobileThese antennae are jointed and mobile Used chiefly to smell and feel (touch)Some insects use antennae to taste and hearAntennae can detect humidity changes, vibrations,

wind velocity and direction, chemical cuesMost insects become distress when antennae damaged

or removed and some are helpless

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Insect Head -- AntennaeAntennae vary greatly among insects but all follow a basic plan w/ 3 main divisions1. basic segment called scape is generally larger than1. basic segment called scape is generally larger than

the other segments; it is inserted into the insect head2. the second segment or pedicel follows the scape

contains a sensory organ known as Johnston’s organ that responds to movement of the distal part of the antenna

3. the remaining part is the flagellum is often filamentous w/ multiple segments

Antennae are reduced or almost absent in some larval insects (e.g. Hymenoptera)

Insect Head -- Antennae

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Insect Head -- AntennaeNumerous variations in the antennae of different insects

Insect Head -- Antennae• Numerous variations in the antennae of different insects

Type Description Found onFiliform thread-like field cricket Setaceous bristle-like cockroachCapitate head-shaped nitudilid beetleClavate tapering club-like butterflyLamellate flat plate-like June beetleMoniliform string of beads termitesSerrate saw toothed click beetleGeniculate elbowed chalcidPectinate comb-like mothPectinate comb like mothPlumose with plumes mosquitoAristate with an arista houseflyFlabellate pile of thick plates cedar beetle

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Insect Head -- MouthpartsMouthparts

Group of structures on the lower part of the head that are adapted to dietare adapted to dietFormed from modified appendages of segments

making the head

As insects take many forms and have a wide range of food types, they also have various mouthparts that can be grouped into two main categories:

Mandibulate (chewing)Haustellate (sucking)

Insect Head -- Mouthparts1. Mandibulate Mouthparts

Most primitive mouthpartsAdapted to solid diets these mouthparts are generallyAdapted to solid diets, these mouthparts are generally

biting and chewingComposed of five primary parts:

clypeusthe upper lip or labrum2 jaw-like structures or mandibles2 jaw-like structures or mandiblesthe maxillae (singular maxilla)the lower lip or labium

Maxillae and labium are further divided into various substructures

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Insect Head -- Mouthparts

Insect Head -- MouthpartsChewing mouthparts are present in

grasshoppers, crickets, locusts, cockroaches, beetles caterpillars (larvae of moths andbeetles, caterpillars (larvae of moths and butterflies)

Black swallowtail caterpillarGrasshopper CricketGround Beetle

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Insect Head -- Mouthparts2. Haustellate Mouthparts

Used primarily for ‘sucking up’ liquids of fluids from plants and animalsfrom plants and animalsHaustellate mouthparts are divided into 2

groups based on:presence or absence of styletstylet is a needle-like projection used to penetrate y p j pplant or animal tissues

Haustellate Mouthparts Insects w/ stylate MP have a stylet used to

Insect Head -- Mouthparts

have a stylet used to pierce and pump up fluids (piercing-sucking)Insects with styletinclude aphids, p ,leafhopper, flies, fleas, mosquitoes

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Haustellate Mouthparts Some haustellate

mouthparts lack stylet

Insect Head -- Mouthparts

mouthparts lack styletUnable to pierce tissue they must rely on easily accessible liquid food such as nectar at the base of flowerbase of flowerInsects with nonstylateMP comprise butterflies, moths which have long siphoning proboscis

Haustellate Mouthparts Some insects w/haustellate

Insect Head -- Mouthparts

mouthparts feed on liquid but also on solid and semi-solid diet by external digestion Solid food is liquefied by digestive fluids before being

k d Th isucked up. These insects have sponging MPE.g. Housefly

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• Haustellate Mouthparts Some insects

/h t ll t

Insect Head -- Mouthparts

w/haustellatemouthparts feed on liquids but also semi-solid diet by lapping labium modified into a hairy tonguehairy tongue E.g. Honeybee

Most common five mouthparts

Insect Head -- Mouthparts

p

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Recognition of the types of mouthparts

Insect Name Mouthpart Plant injury

Insect Head -- Mouthparts

type

? Chewing Hole in leaves

Aphid ? Removal of juices

Honey bee Lapping ?

Insect ThoraxThorax is the locomotor tagmaThe thorax of insect consists of 3 segments

prothorax (pro = first)p (p )

mesothorax (meso = middle)

metathorax (meta = last)

Each segment consists of hardened plates or scleritesDorsal sclerite is notum (plural nota), lateral sclerite is pleuron (plural pleura) and ventral one is sternum (pluralpleuron (plural pleura) and ventral one is sternum (plural sterna)Each of the 3 thoracic segment contains one pair of legsWings are found only on the meso- and meta-thorax. No wings on the prothorax

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Insect Thorax

Legs• 3 pairs of legs (6 total)

Fore legs (2) on the prothorax

Insect Thorax

Fore-legs (2) on the prothoraxmid-legs (2) on the mesothoraxhind-legs (2) on the metathorax

• Each leg has 6 major componentscoxa (plur. Coxae)t h ttrochanterfemur (plur. femora)tibia (plur. tibiae)tarsus (plur. tarsi)pretarsus (plur. pretarsi)

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Insect Thorax Legs

Femur and Tibia are generally the longest segments

Leg modification: Insect legs are modified for adaptation to various functions

walking (gressorial or ambulatorial) like in field cricketi ( i l) lik i h

Insect Thorax

running (cursorial) like in roachesgrasping (raptorial) like in praying mantisdigging (fossorial) like in Gryllotalpa (ground-dwelling insects)clinging (scansorial) like in fleashearing (tympanum) like in prothoracic leg of grasshopperswimming (natatorial) like in scavenger beetleswimming (natatorial) like in scavenger beetlejumping (saltarorial) like in hind legs of grasshopperclasping legs in some males to hold females, e.g. Dytiscus malemaking sound (stridulatory organ) like in tettigoniidcollecting food like pollen, e.g. metathoracic leg of bees

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Insect Thorax -- Common types of legs

WingsWhen present, wings arise from the meso- and metathorax, but many insects are wingless (without wings or

Insect Thorax

metathorax, but many insects are wingless (without wings or apterygota)Typically, there are 2 pairs of wings, but in few groups wings are reduced to one pair (true flies or Diptera)Wings are mostly membranous but in beetles the forewings (elytra) are hard cases and do not take part of flight( y ) p gMembranous wings are supported by thickened ribs called veinsPattern of arrangement of these veins used in insect classification

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Wing regions Insect Thorax

Insect Thorax -- Wing Variation- Elytra for protection

- Halteres: hind wings completely reduced to mere nubs used for b l d di i d i fli h

- In some male insects, sound producing mechanisms (file and scraper)are present on the underside of forewings and forelegs-- sound used mating calls (e.g. male grasshopper).

balance and direction during flight (e.g. true flies)

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Insect Abdomen• Insect abdomen has 11 segments although segment 1 may be

reduced or incorporated into the thorax (e.g. Hymenoptera) and the last 2 segments are variously modified or diminished

• hard dorsal part of abdomen is tergum (terga) and ventral part is• hard dorsal part of abdomen is tergum (terga) and ventral part is sternum (sterna)

• Dorsal and ventral plates are joined together by a soft inter-segmental membranes

• There are small dark openings (spiracles) set into the soft membranous area, each along side the abdomen-- one pair on each

tsegment• 2 pairs of spiracles are also present on the thorax • a pair of cerci of the 11th abdominal segment; cerci permit

sensory pickup from the back

Insect Abdomen

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Insect AbdomenAbdomen hosts major viscera, heart, and reproductive organsReproductive organs are located on the 9th segment for males (aedegus or penis and often a pair of claspers) and on the 8th and 9th abdominal segments for females (external genitalia or copulatory openings and ovipositor g p y p g pfor egg laying)In higher Hymenoptera, the ovipositor is modified to form a poison injecting apparatus, the sting (wasps, bees) used for defense

Summary of Insect Body

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Study questions• How many segments can be found on a primitive insect?• What are the main tagmata of an insect?• Are there spiracle on a) head?, b) thorax?• How many ocelli are present on an insect?y p• What is the function of antennae?• Why are they modifications of insect legs?• What are the two major groups of insect mouthparts?• What are the major functions of an insect head and how do these

compare with those of other animal heads?• Name the major appendages associated with the insect head?• What is the major function of insect thorax? • How many segments make up the thoracic region, 20, 11, 9 or 3?• Are wings found on all stages and all insects?• What is an ovipositor?