Biology 320Biology 320Invertebrate ZoologyInvertebrate ZoologyFall 2005Fall 2005

Chapter 21 – Phylum Arthropoda, Chapter 21 – Phylum Arthropoda,

Superclass HexapodaSuperclass Hexapoda

Class InsectaClass Insecta

Majority of all animalsMajority of all animals

1,000,000 described species1,000,000 described species Estimated 10 to 30 million undescribedEstimated 10 to 30 million undescribed

Do not live in oceans, with the Do not live in oceans, with the exception of a few intertidal speciesexception of a few intertidal species

Well adapted for terrestrial existenceWell adapted for terrestrial existence 2 – 250 Malpighian tubules2 – 250 Malpighian tubules Many other adaptations and behaviorsMany other adaptations and behaviors

Holometabolus (indirect) development Holometabolus (indirect) development has led to success on land by has led to success on land by promoting resource partitioningpromoting resource partitioning Largest insect orders (Lepidoptera, Largest insect orders (Lepidoptera,

Hymenooptera, and Diptera) exhibit indirect Hymenooptera, and Diptera) exhibit indirect developmentdevelopment

Insect flight allows for:Insect flight allows for: DispersalDispersal Predator escapePredator escape Access to food and optimum Access to food and optimum

habitathabitat

Many have interesting Many have interesting coevolutionary relationships coevolutionary relationships with flowering plantswith flowering plants

Some are vectors of Some are vectors of diseasedisease

Herbivory by insects does Herbivory by insects does large amounts of damage to large amounts of damage to cropscrops

Body FormBody Form

Three tagmataThree tagmata

HeadHead Two compound eyesTwo compound eyes Three unpaired ocelliThree unpaired ocelli One pair of antennaeOne pair of antennae Preoral cavity with complex Preoral cavity with complex

mouthpartsmouthparts

ThoraxThorax Three pairs of legsThree pairs of legs

ForelegsForelegs Middle legsMiddle legs Hind legsHind legs

Thorax cont…Thorax cont… Two pairs of wings in most Two pairs of wings in most

adults, while juveniles have adults, while juveniles have wing padswing pads

Some only have one pairSome only have one pair Some lack altogetherSome lack altogether Some only possess wings Some only possess wings

during reproductive periodsduring reproductive periods

AbdomenAbdomen Typically 9 – 11 segmentsTypically 9 – 11 segments Female gonopore on Female gonopore on

segment 8segment 8 Male gonopore on segment 9Male gonopore on segment 9 Some have sensory Some have sensory

appendages called cerci on appendages called cerci on last segmentlast segment

Wings and FlightWings and Flight

Wings composed of two sheets Wings composed of two sheets of epidermis covered with cuticleof epidermis covered with cuticle

Sclerotized areas called veins Sclerotized areas called veins offer supportoffer support HollowHollow House tracheae, nerves, and House tracheae, nerves, and

bloodblood

Permanently outstretched wings Permanently outstretched wings is a primitive traitis a primitive trait

The evolution of wing folding has The evolution of wing folding has allowed insects to exploit allowed insects to exploit microhabitats where outstretched microhabitats where outstretched wings would be a handicap wings would be a handicap

Flight muscles fill most of the thoraxFlight muscles fill most of the thorax Striated fibers with huge mitochondria, and profuse tracheal innervation (to Striated fibers with huge mitochondria, and profuse tracheal innervation (to

meet high oxygen demand)meet high oxygen demand)

Wings move up, down, forwards, and backwardsWings move up, down, forwards, and backwards Wing angles are frequently changedWing angles are frequently changed

Insects are probably the most skilled flyersInsects are probably the most skilled flyers Houseflies can outperform any birdHouseflies can outperform any bird

Can turn in the distance of one body lengthCan turn in the distance of one body length Can fly upside downCan fly upside down

Hummingbird moths and botflies can fly 25 mphHummingbird moths and botflies can fly 25 mph

Display positive phototaxis, and often fly into lampsDisplay positive phototaxis, and often fly into lamps

NutritionNutrition

Diverse nutritional Diverse nutritional strategies, and thus strategies, and thus diversity in mouthpart diversity in mouthpart structure and functionstructure and function

Mandibulate mouthpartsMandibulate mouthparts Grasshoppers and antsGrasshoppers and ants Large jaws for cutting and Large jaws for cutting and

chewingchewing Found in many herbivores Found in many herbivores

and carnivoresand carnivores

Sucking mouthpartsSucking mouthparts Butterflies and mothsButterflies and moths Suck nectar and fruit juices with a Suck nectar and fruit juices with a

long proboscis formed from maxillaelong proboscis formed from maxillae Rolled and coiled when not feedingRolled and coiled when not feeding Diet is N and Na deficient so they Diet is N and Na deficient so they

drink other types of liquids (mud drink other types of liquids (mud puddles, carrion, animal wastes, puddles, carrion, animal wastes, etc.) to supplementetc.) to supplement

Piercing mouthpartsPiercing mouthparts Aphids drink plant juicesAphids drink plant juices Female mosquitoes require a blood Female mosquitoes require a blood

meal to produce eggsmeal to produce eggs Stylet pierces preyStylet pierces prey

Has a salivary channel and a food Has a salivary channel and a food channelchannel

Proteins in saliva produce itching Proteins in saliva produce itching associated with mosquito bitesassociated with mosquito bites

Surrounding structures support Surrounding structures support styletstylet

Sponging mouthpartsSponging mouthparts Nonbiting fliesNonbiting flies Enlarged labium is used Enlarged labium is used

to absorb liquidsto absorb liquids Liquefy food with Liquefy food with

enzymesenzymes

Digestive systemDigestive system Salivary glands produce Salivary glands produce

many types of secretionsmany types of secretions Pectinase for breaking Pectinase for breaking

down plant cell wallsdown plant cell walls Typical secretionsTypical secretions Some have silk glands in Some have silk glands in

place of salivary glandsplace of salivary glands Used for making Used for making

cocoonscocoons

Digestive system cont…Digestive system cont… Peritrophic membranePeritrophic membrane

Protects non-cuticularized midgutProtects non-cuticularized midgut Partitions areas where digestive enzymes functionPartitions areas where digestive enzymes function

Membrane is perforated, so some enzymes pass through Membrane is perforated, so some enzymes pass through membrane and act on food bolusmembrane and act on food bolus

Hydrolyzed biomolecules pass from bolus side to lumen Hydrolyzed biomolecules pass from bolus side to lumen sideside

Additional enzymes facilitate further digestionAdditional enzymes facilitate further digestion

Midgut has two to six gastric cecaMidgut has two to six gastric ceca

Hemocoel contains a fat body that synthesizes Hemocoel contains a fat body that synthesizes and stores biomoleculesand stores biomolecules

Hemal SystemHemal System

Not many vesselsNot many vessels

Accessory hearts pump blood to important Accessory hearts pump blood to important structures (antennae, mouthparts, legs, structures (antennae, mouthparts, legs, wings, cerci, etc.)wings, cerci, etc.) Located at bases of extremitiesLocated at bases of extremities

Many insects can survive subfreezing Many insects can survive subfreezing temperatures (-30temperatures (-30°C)°C) Compounds in blood, such as glycerol, function as Compounds in blood, such as glycerol, function as

antifreezeantifreeze

Respiratory SystemRespiratory System Elaborate tracheal systemElaborate tracheal system

Branch and diverge into a network Branch and diverge into a network of smaller and smaller tubesof smaller and smaller tubes

Smallest tubes are called Smallest tubes are called tracheoles (make direct contact tracheoles (make direct contact with cells)with cells)

10 pairs of spiracles10 pairs of spiracles Two pairs on thoraxTwo pairs on thorax

Spiracles can be closed, which Spiracles can be closed, which prevents:prevents: Water lossWater loss Dust from enteringDust from entering Parasites from enteringParasites from entering

Cartilagenous support rings Cartilagenous support rings

Sensory OrgansSensory Organs

Most are derived from setae and Most are derived from setae and are associated with appendagesare associated with appendages Tarsi of many have gustatory (taste) Tarsi of many have gustatory (taste)

or tactile (touch) receptorsor tactile (touch) receptors Flies taste food by walking on itFlies taste food by walking on it

EyesEyes Form color images in someForm color images in some Some (especially pollinators) are Some (especially pollinators) are

sensitive to UV lightsensitive to UV light

Reproductive SystemReproductive System Gonochoric with internal fertilizationGonochoric with internal fertilization

Female systemFemale system Two ovaries produce eggs with a waterproof capsuleTwo ovaries produce eggs with a waterproof capsule Two oviducts converge and empty into a vaginaTwo oviducts converge and empty into a vagina Oviduct opens on segment 8Oviduct opens on segment 8 Tubular ovipositor for depositing eggs in appropriate substratum (i.e. Tubular ovipositor for depositing eggs in appropriate substratum (i.e.

soil, wood, plant, animal, etc.)soil, wood, plant, animal, etc.) Ovipositor is modified to form a sting with poison glands in some Ovipositor is modified to form a sting with poison glands in some

Hymenopteran females Hymenopteran females

Male systemMale system Two testes with sperm ductsTwo testes with sperm ducts

Accessory glandsAccessory glands

Median ejaculatory ductMedian ejaculatory duct

Penis is extensible / Penis is extensible / retractableretractable Everts through gonopore on Everts through gonopore on

segment 9segment 9 Releases spermatophore or Releases spermatophore or

spermsperm Sperm plug (mating plug)Sperm plug (mating plug)

May have claspers for holding May have claspers for holding female during copulationfemale during copulation

Sperm enter egg through a Sperm enter egg through a micropyle in egg capsulemicropyle in egg capsule

Insect DevelopmentInsect Development

Under hormonal controlUnder hormonal control

Three main stages:Three main stages: EggEgg

JuvenileJuvenile Many instars separated by Many instars separated by

moltsmolts Main role is to feed and growMain role is to feed and grow

AdultAdult Technically termed an imagoTechnically termed an imago Sexually mature with functional Sexually mature with functional

wingswings May / may not continue to moltMay / may not continue to molt Main role is dispersal and Main role is dispersal and

reproductionreproduction

Direct DevelopmentDirect Development

Three main typesThree main types

Paurometabolous Paurometabolous development is the only development is the only type we will discusstype we will discuss Grasshopper, cockroaches, Grasshopper, cockroaches,

etc.etc. Juveniles are morphologically Juveniles are morphologically

similar to adultssimilar to adults Adults don’t moltAdults don’t molt Does not promote resource Does not promote resource

partitioningpartitioning Adults and nymphs in Adults and nymphs in

competition with one anothercompetition with one another

Indirect DevelopmentIndirect Development Holometabolus developmentHolometabolus development

Hymenopterans, flies, beetles, and LepidopteransHymenopterans, flies, beetles, and Lepidopterans

Juveniles (larvae) are wormlike, and called grubs, maggots, or Juveniles (larvae) are wormlike, and called grubs, maggots, or caterpillarscaterpillars

Many larval instarsMany larval instars

Pupa phase between last instar and imagoPupa phase between last instar and imago Undergoes metamorphosisUndergoes metamorphosis

Imago has wings and looks nothing like juvenileImago has wings and looks nothing like juvenile Different mouthparts, and therefore they feed on different types of Different mouthparts, and therefore they feed on different types of

foodsfoods

Promotes resource partitioningPromotes resource partitioning

CoevolutionCoevolution Definition - evolution of plants and insects in response to Definition - evolution of plants and insects in response to

one anotherone another

Plants and insects are vital to each otherPlants and insects are vital to each other Plants provide food (nectar, pollen, and plant tissues) and shelter Plants provide food (nectar, pollen, and plant tissues) and shelter

to insectsto insects Insects pollinate plantsInsects pollinate plants

Bees, wasps, butterflies and Bees, wasps, butterflies and moths are the primary insect moths are the primary insect pollinatorspollinators

Insects pollinate 70% of all Insects pollinate 70% of all flowering plantsflowering plants

Plants adapt to make Plants adapt to make improvements that minimize improvements that minimize costs to both organisms, and costs to both organisms, and maximize efficiency of pollination maximize efficiency of pollination processprocess Characteristic colors, odors, and Characteristic colors, odors, and

nectars to attract insectsnectars to attract insects Guide marks and UV-sensitive Guide marks and UV-sensitive

patterns on flowerspatterns on flowers Time that flowers bloom Time that flowers bloom

coincides with periods of insect coincides with periods of insect activityactivity

Coevolution in response to Coevolution in response to herbivoryherbivory

Plants have evolved a suite of Plants have evolved a suite of defenses against insect herbivorydefenses against insect herbivory

Mechanical – spines, bristles, and Mechanical – spines, bristles, and hairshairs

Chemical – nicotine, caffeine, Chemical – nicotine, caffeine, cyanide, and tanninscyanide, and tannins

In turn, insects develop counter In turn, insects develop counter offensesoffenses

Enzymes that detoxify protected Enzymes that detoxify protected tissuestissues

These insects specialize on These insects specialize on plants they can detoxify, and plants they can detoxify, and have little competitionhave little competition

Defensive chemicals may Defensive chemicals may become attractantsbecome attractants

Arms race continuesArms race continues

GallsGalls

Another interesting aspect of insect-Another interesting aspect of insect-plant relationships is gall formationplant relationships is gall formation

Many herbivorous insects cause Many herbivorous insects cause plants to form gallsplants to form galls Swollen portion of plant tissue Swollen portion of plant tissue

containing eggs or larvaecontaining eggs or larvae Forms in response to compounds Forms in response to compounds

secreted by ovipositing female and secreted by ovipositing female and larvaelarvae

Gall shape is characteristic of the Gall shape is characteristic of the insect that laid eggsinsect that laid eggs

Gall protects larvae, larvae feed on Gall protects larvae, larvae feed on gall tissue; eventually emergegall tissue; eventually emerge

ParasitismParasitism Fleas, lice and biting flies are Fleas, lice and biting flies are

parasiticparasitic

Usually only one life phase is Usually only one life phase is parasiticparasitic

Human botfly (Human botfly (DermatobiaDermatobia)) Captures a mosquito or biting flyCaptures a mosquito or biting fly Deposits eggs on the captured fly Deposits eggs on the captured fly

and releasesand releases Recently captured insect bites a Recently captured insect bites a

human or other animalhuman or other animal Egg falls into woundEgg falls into wound Grub develops in a cavity called a Grub develops in a cavity called a

warblewarble Molts several timesMolts several times Crawls to surface, falls to ground and Crawls to surface, falls to ground and

pupatespupates

ParasitoidismParasitoidism

Insects that parasitize larger Insects that parasitize larger insectsinsects

Typically deposit eggs in or Typically deposit eggs in or on host using an ovipositoron host using an ovipositor

Eggs hatch and consume Eggs hatch and consume hosthost

Very commonVery common It has been hypothesized that It has been hypothesized that

each insect species has a each insect species has a parasitoidparasitoid

Parasitoids are important for Parasitoids are important for controlling insect populationscontrolling insect populations

Example 1: Example 1: Wasp secretes chemical that Wasp secretes chemical that

causes worker ants to fight each causes worker ants to fight each otherother

While ants fight, wasp enters While ants fight, wasp enters nest and oviposits on larvaenest and oviposits on larvae

Example 2:Example 2: ApantelesApanteles (wasp) oviposits in (wasp) oviposits in ManducaManduca (Sphinx moth) larvae (Sphinx moth) larvae

Up to 500 larvae can grow inside Up to 500 larvae can grow inside caterpillarcaterpillar

Rupture body wall and form Rupture body wall and form cocoon on surfacecocoon on surface

CommunicationCommunication Pheromones Pheromones

Chemicals used for:Chemicals used for: Attracting potential matesAttracting potential mates Marking territories and trailsMarking territories and trails Locating and removing dead Locating and removing dead

individuals from colonyindividuals from colony DefenseDefense Warning conspecifics of Warning conspecifics of

dangerdanger Locating foodLocating food

Usually dispersed by windUsually dispersed by wind

Effective in very small Effective in very small quantitiesquantities

FlashingFlashing FirefliesFireflies Species-specific flashing patternSpecies-specific flashing pattern Some female fireflies mimic Some female fireflies mimic

flashing patterns of other speciesflashing patterns of other species Attracts male of a different Attracts male of a different

speciesspecies Female preys upon maleFemale preys upon male

SoundSound Stridulation is produced by wings Stridulation is produced by wings

and leg filesand leg files Other types of sound produced Other types of sound produced

by wing beating, forcing air from by wing beating, forcing air from tracheae, etc.tracheae, etc.

Social InsectsSocial Insects Isopterans (termites) and Isopterans (termites) and

Hymenopterans (bees, wasps, and ants)Hymenopterans (bees, wasps, and ants)

All groups share several characteristicsAll groups share several characteristics One queen that mates with other fertile One queen that mates with other fertile

individuals (drones)individuals (drones) Physical labor is carried out by sterile Physical labor is carried out by sterile

individualsindividuals Caring for juvenilesCaring for juveniles ForagingForaging SoldiersSoldiers

No individual can exist independent of No individual can exist independent of colonycolony

No individual can be accepted into a No individual can be accepted into a colony other than its owncolony other than its own

However, some ants raid nests of other However, some ants raid nests of other species, kidnap pupae, raise juveniles, species, kidnap pupae, raise juveniles, and force them to work as slavesand force them to work as slaves

Characteristics…Characteristics… Caste systemCaste system

Individuals with different morphologiesIndividuals with different morphologies Have different dutiesHave different duties Examples: soldiers, workers, and dronesExamples: soldiers, workers, and drones

Ants and termites usually inhabit Ants and termites usually inhabit elaborate colonies with many elaborate colonies with many tunnels, chambers, entrances and tunnels, chambers, entrances and exitsexits Army ants are an exceptionArmy ants are an exception Leaf cutter ants have chambers for Leaf cutter ants have chambers for

growing fungusgrowing fungus

Colony formationColony formation In bees, new queens are produced In bees, new queens are produced

when larvae eat a substance known as when larvae eat a substance known as “royal jelly” that is produced by the “royal jelly” that is produced by the hypopharyngeal glands of nursery hypopharyngeal glands of nursery workersworkers

Queen usually takes part in nuptial flight Queen usually takes part in nuptial flight in order to start new colonyin order to start new colony

In bees 20,000 to 60,000 individuals will In bees 20,000 to 60,000 individuals will swarm and search for a new colony swarm and search for a new colony locationlocation

DiversityDiversity

There are around 30 insect There are around 30 insect ordersorders We will We will brieflybriefly cover 14 cover 14

Order OdonataOrder Odonata Dragonflies and damselfliesDragonflies and damselflies Voracious predators found near Voracious predators found near

waterwater Nymphs are aquaticNymphs are aquatic Dragonflies are heavy bodied with Dragonflies are heavy bodied with

outstretched wingsoutstretched wings Damselflies are more slender and Damselflies are more slender and

delicate, with wings held over delicate, with wings held over abdomen while at restabdomen while at rest

Order OrthopteraOrder Orthoptera Grasshoppers, crickets, and Grasshoppers, crickets, and

katydidskatydids Large insects with large Large insects with large

compound eyescompound eyes Large hind legs for jumpingLarge hind legs for jumping Stridulating and auditory Stridulating and auditory

organsorgans HerbivoresHerbivores

Order PhasmidaOrder Phasmida Walking sticksWalking sticks Mimic sticks or vegetationMimic sticks or vegetation Elongate and cylindrical Elongate and cylindrical

bodiesbodies Usually lack wingsUsually lack wings Some up to 30cm longSome up to 30cm long

Order DermapteraOrder Dermaptera EarwigsEarwigs Nocturnal and omnivorousNocturnal and omnivorous Elongate bodyElongate body Large pincer-like cerci Large pincer-like cerci

Order IsopteraOrder Isoptera TermitesTermites Soft bodied and pale in colorSoft bodied and pale in color Build large mounds or nests in Build large mounds or nests in

treestrees Can infest buildingsCan infest buildings Have endosymbiotic microbes Have endosymbiotic microbes

that produce cellulasethat produce cellulase

Order MantodeaOrder Mantodea MantidsMantids Large and slow movingLarge and slow moving Cryptic colorationCryptic coloration Ambush predators with Ambush predators with

raptorial forelegsraptorial forelegs Large eyes on a freely Large eyes on a freely

movable headmovable head

Order BlattariaOrder Blattaria CockroachesCockroaches Fast runnersFast runners NocturnalNocturnal OmnivorousOmnivorous Endosymbionts similar to Endosymbionts similar to

those of termitesthose of termites

Order PhthirapteraOrder Phthiraptera LiceLice Ectoparasites of mammals and birdsEctoparasites of mammals and birds Prehensile legs for clinging to hair or Prehensile legs for clinging to hair or

feathersfeathers WinglessWingless All life stages are spent on hostAll life stages are spent on host Host to host physical contact is Host to host physical contact is

required for transmissionrequired for transmission

Order HemipteraOrder Hemiptera True bugsTrue bugs Stink bugs, water striders, aphids, and Stink bugs, water striders, aphids, and

cicadascicadas Sucking mouthparts for ingestion of Sucking mouthparts for ingestion of

liquidsliquids Herbivory is of economic significanceHerbivory is of economic significance Some are vectors of plant or animal Some are vectors of plant or animal

diseasedisease

Order ColeopteraOrder Coleoptera BeetlesBeetles Largest order at Largest order at

approximately 600,000 approximately 600,000 speciesspecies

Extremely sclerotizedExtremely sclerotized Forewings are called elytraForewings are called elytra

Most are herbivores, but Most are herbivores, but ladybird beetles are ladybird beetles are carnivorouscarnivorous

Order HymenopteraOrder Hymenoptera Ants, wasps and beesAnts, wasps and bees Chewing mouthpartsChewing mouthparts Most have wings, but worker Most have wings, but worker

ants lackants lack In females, ovipositor may be In females, ovipositor may be

a stinga sting Maggot-like larvaeMaggot-like larvae

Order LepidopteraOrder Lepidoptera Butterflies and mothsButterflies and moths Adults have a coiled proboscisAdults have a coiled proboscis Drink nectar and fruit juicesDrink nectar and fruit juices Larvae are herbivorous caterpillarsLarvae are herbivorous caterpillars Cocoon or chrysalis is constructed Cocoon or chrysalis is constructed

for pupa phasefor pupa phase

Order SiphonapteraOrder Siphonaptera FleasFleas Small and winglessSmall and wingless Laterally compressedLaterally compressed Ectoparasites of mammals and Ectoparasites of mammals and

birdsbirds Excellent jumpersExcellent jumpers Larvae aren’t parasiticLarvae aren’t parasitic Some are vectors of disease like Some are vectors of disease like

bubonic plaguebubonic plague

Order DipteraOrder Diptera True fliesTrue flies Mosquitoes, houseflies, Mosquitoes, houseflies,

gnats, and cranefliesgnats, and craneflies Large compound eyesLarge compound eyes Feed on animal or plant Feed on animal or plant

fluidsfluids Some are vectors of Some are vectors of

diseasedisease Eggs deposited in wet Eggs deposited in wet

substrata such as flesh, substrata such as flesh, fruit, or waterfruit, or water

Larvae called maggotsLarvae called maggots