Sensory Neurons

interneuronss

motor neurons

mechanoreception

chemoreception

photoreception

Trichoid Sensilla

hairplates

campaniform sensilla

chortotonal organs

tympana

stretch receptors

hair/bristles

(exteroceptors/proprioceptors)

percieve changes in air pressure, tactile stimuli, or airborne vibrations(sound)

Trichoid sensilla

externally composed of...

1.cuticular apparatus

2. well developed socket

trichoid sensilla

internally composed of...

1. sensory neuron

2.accessory cells

-grow the cuticular apparatus

-grow the socket

-provide accessory fluids

1. Form and function-shape of sensory sturctures correlated to type of info collected

-thin and long for air currents

-spine like for physical contact with stimuli

-clavate for gravity

2. Sensory neurons foucused to certain stimuli

3.Location

Prey detection by the trap-jaw ant

hairs trigger mandibles to snap shut

can use mechanism for defense

Prey holding and manipulation

ex. Airborne sounds in caterpillars

many caterpillars have hairs on thorax that can detect wing frequency of predators

freeze in motion

wiggle and drop

Proprioceptors:composed of multiple trichoid sensilla

flexing of the cuticle w/respect to other parts of the body triggers a response

legs

head relative to thorax

antennal segments

position of wings

body relative to gravity

Proprioceptors

-dome shaped apparatus surrounded by a socket

found in areas that recieve pressure or tension

legs

mouthparts

antennae

ex. calliphora-blow flies

adult has 1200

found throughout the body to measure mechanical distortion

mostly proprioceptors but can also be exteroceptors

often connect two landmarks on an insect

ex. drosophilia larvae ahve 90

Chordotonal organs

found on...

wing bases

neck regions

all legs

antennae

abdominal segments

1 to many Scolopidia

1. cap/attachment cell- attachment to epidermis

2. scolopale cell-composed of fibrous flexible material, wraps around dendrite of sensory cell

3. sensory cell-detects distortion of it cilium(microtubules) cause by movement of the cap

Chordotonal Organs

Examples

Johnston's Organ

measures the distortion of the flagellum relative to the pedicel

Proprioceptor:

gravity

flight speed

position of antenna

Exteroceptor:

vibrations

measure size of objects

water surface changes

ex. whirly gig beetles, male mosquito

Chordotonal ORgan

Example #2

Subgenual organs

detect vibrations on proximal tibia of most insects (except bees and flies

communication (ants, leaf hoppers, caterpillars)

detection of prey/predators

Evolution of Insect ears

From chordotonal organs to tympanal organs

Tympanal Organs

3 important components

1. Tympanum(ear drum)

2. an air filled sac ot tracheal space behind tympanum

3. an auditory receptor unit, few to many neurons

proprioceptorswith free nerve endings: detect stretching

on inside of epidermis (monitor changes in body shape)

gut expansion(regualte meal size, monitor food levels)

reproductive organs

Beginning of Photoreception

Physiology of vision

light gathered and focused by cornea and lens>

onto sensory cells(retina)>

sensory cells contain pigments>

action potentials generate by pigments absorbing energy

images, color, motion

ommatidium is 1 unit

each ommatidium gets light info

brain pieces together info into an image

Light focused by lens and cone

retinula cells are neuronal conenction to the brain

microvilli of retinula cells form a rhabdom

covered with visual pigments

apterygote insects

strepsiptera

group of ommatidia

1 in some ants

10,000 in dragonflies

holoptic

eye around antenna

4 eyes

ex. whirlgig beetle, milkweed beetle

predators zero in on prey

herbivore host selection

pollinators

maitng triggered by chemical, auditory, tacticle, visual signals

male mate selection

female choice

more light at expense of resolution

ex. moths

stemmata (stemma)

ocelli(ocellus)

adult flying insects

out of focus...

horizon detection

larva holometabolous insects

ex. isia

blood-sucking bugs

wood-boring beetles

butterfly genitalia

beetle epidermis

detection of compounds in solution or liquid state: analogous to "taste"

direct contact with substrate needed

ex. caterpillars taste receptors on mouth

ex. ants have taste recpetos on antenna

ex.nympahalid butterflies, bees

taste receptors on tarsi

Marking phermones

detection of compounds in gaseous state

can be over shout/long distances

Function:feeding, oviposition cues, mate recognition/selection

Distribution: antennae, maxillary and labial palps

legs, ovipositors, wings

# of pores:single

# of receptors: 2 to 5

mechanoreception: often

Where is the info processed: terminates at nearest ganglion/brian

Olfaction Detail

function: localization of food, oviposition sites, mates

distribution:antennae and maxillary and labial palps

# of pores: multiporous

# of receptors: 2 to many

Mechanoreception: no

Where is the info processed? brain

the growth stage between two successive molts (discrete)

juvenile stages

Determinant

or

Indeterminant

continue to molt throughout life but do not grow larger

ex. collembola, diplura

having a set number of molts

ex. winged insects

gradual change in form with juveniles similar to body form to the adults. WIngs are fully developed as adults

incomplete metamorphosis

Exopterygotes

Juvenile and adult forms are morphologically distinct; a larva, pupa, and adult stage

complete metamorphosis

ex. butterfly

Endopterygotes

adult structures that develop with in juveniles in invaginated pockets

(wings, eyes, genitalia, and mouthparts)

What do we call juvenile stage?

Naiads

Nymphs

Larvae

the aquatic juvenile stages of hemimetabolous insects

ex. mayflies, dragonflies, stoneflies

the terrestrial juvenile stages of Ametabolous and Hemimeabolous insects

ex. collembola, grasshoppers, bugs, roaches

the juvenile stages of holometabolous insects (whether terrestrial or not)

ex. beetle, flies, bees, wasps, butterflies

Molting and the Integument 8 steps

1. Mitosis-cells divide and become columnar in shape

apolysis-separation of epidermis from old cuticle;exuvial space forms

2. Inactive molting fluid-secreted into exuvial space, chitinases and proteases

3. New epicuticle produces below molting fluid

4. molting fluid activated by Na+ and H20

-digestion of old cuticle initiated

90% of endocuticle can be reabsorbed

5. Procuticle production begins  (procuticle laid down in layers)

6. was and cement layers added

 pre-ecdysis behavior-uptake h20, purgin the stomach, insects find appropriate molting sites, uptake of air, partial rotary movements

7. Ecdysis- shedding of old skin

8.sclerotization of new cuticle-formation of exocuticle

post-ecdysis behavior- stretching and expandin while new cutilce hardens

-eventually water is elminated

Hormones and Molting

Important players

1. Neuroecretory cells in the brain

2. Corpus cardiacam.corpus allata (paired glands

3. prothoracic gland (paired)

4. CNS/brain

Steps

Step 1:

Trigger could vary between insects

Examples:

a. kissing bud

-stretch receptors on wall of abdomen

b.sphinx moth

-uses weightad trigger

External cues such as day length, temperature may also play a role in some insects

triggers mitosis in epdiermal cells

apolysis

production of epicuticle

triggers production of eclosion hormones by CNS/brain

Eclosion hormone produces by CNS/Brain=

pre and post ecdysis behavior

Bursicon produced by CNS/brain=a post eclosion hormone

Triggered by muscular contractions:

1. increases plasticity of cuticle

2. initiate scleritization

Juvenile hormone is the answer

produced by corpus alllatum

presend during molt=juvenile

absent=adult

migration behaviors/physiology

sperm/accessory gland production

egg development

changes in morph determination(horned/non-horned, scarabs, ant caste system)

1. Kopec 1917

wokred with tent caterpillars

previously not believed that insects used hormones

Brain is not important

2. Wigglesworth 1930s

the substance is in the hemolymph

3. williams 1940s

does the brain hormone directly regualte molting?

Brain hormone does not act directly on epidermis has tropic affect on prothoracic glands. Therefore:

brain hormone=prthoracicotropic hormone=PTTH

pyrrhocoris apterus brought from Europe by Slama and williams

what caused insect to keep molting?

JH Mimic form paper towels

JH mimics found in many plants

cotesia cogreta and manduca sexta

host experiences super elevated levels of JH induced by parasatoid latvae

caterpilla can molt but will never pupate

Beginning Reproduction

Morphology and development

Ectodermal Female

genital chamber

accessory glands

spermatheca

spermathecal gland

common oviduct

ovaries

ovarioles/oocytes

calyx

lateral oviduct

glues, substances for ootheca

defensive compounds, toxins (bees, wasps)

marking, trail phermones

leads to bursa copulatrix

fertilazation takes place where accessory glands and common oviduct meet

Synovigenic

most insects

proovigenic

some lepidoptera/hymenoptera

leads from ovary into lateral oviduct

eggs may be stored here

Calyx in some inchneumonid and braconid wasps can harbor polydna virons

ejaculatory duct

intromittent organ (aedeagus)

paired testes

vas deferens

accessory glands

sperm is quite variable morphologically

found across many orders(lepidoptera,diptera)

non-fertilizing sperm

nutiriton for female, help move fertilizing sperm

elimination of rival sperm

cheap filler to delap reamting

blocking

production/storage

seminal fluid for spermatophores

mating plugs

fecundity enhancing, receptively inhibiting and toxic chemicals

ex. drosophilia: males produce toxic seminal fluids

male intromittent organ

often a very important character for identification

can be very elaborate

used as sensory structure, sperm removal, courtship, weapon

ex. burchid beetle

oviparity

ovoviviparity

viviparity

juveniles develop within eggs that remain within the females body until they hatch or are about to hatch

ex. roaches, flies

live birth

ex. some flies, aphids

sexual reproduction

polyembryony

parthogenesis

alternation of generations

Sperm and egg fuse to form a diploid zygote. Progeny are genetically unique

found in most insects

a single egg gives rise to 2 to many identical offspring(up to 3,000)

ex.parasatoid wasps

development of progeny from unfertilized eggs

1. Thelytoky-development of females from unfertilized eggs

daighters are clones of mother

Evolves often

in all orders but odonata/neroptera,/siphonaptera

can be facultative or obligate

Arrhenotoky-development of males from unfertilized eggs

both sexual and asexual reproduction

ex. aphid/gall wasps

typically a seasonal shift

Sex determination

Wolbachia

bacterium that is transferred to offspring via the cytoplasm of the eggs

eliminates males

kills male eggs

feminizing the male embryo

induce thelytoky

1. obligate

2. alternative strategies

3. conditional strategies

Mating behaviors can be dynamic

Obligate:

everyone does the same thing

explosive short live mating assemblages

ex. termites/ants mate right after a rain

Alternative Strategies

fixed strategies

genetic polymorphism

different strategies are the result of individuals having different genes taht code for the strategies

Requires that..

the net pay off to each morph will be equal

or

fluctuating selection muct favoe different genotypes at different times

ex. rock paper lizards

Conditional Strategies

mixed strategies

genetic morphism

Tactics:

ALternative Phenotypes

tactics:

Alternative behaviors

copulate with females when they exit tunnels

enter tunnels when maels exit

dig side tunnels to access females

alternative behavior

examples

female mimics

rove beetles may mimic females

gain access to food and females

large males defend dead insects that attract recpetive females

medium sized males secrete saliva on leaves and wait for females

small males offer nothing and force female to copulate

Fossils

First insects

Early devonian

insect:wingless, soil dwellers, detrivores

carboniferous

a great mystery

paleoptera- old winges insects

neoptera new winges insects

Carboniferous

Arthopleurida- giant millipedelike creature

meganeura-giant dragonflies

Large mayflies with feeding mouthparts

Paledictyoptera-super suckers

-large,divers

-piercing sucking mouthaprts

early plant insect interactions

insects have an open tracheal system

this constrains their abililty to be large

can't diffuse oxygen over too large an area

can therfore diffuse oxygen over a larger body size

greater density of air=hight reynolds number=better genertaion of lift

carboniferous

miomptera-an extinct group, poorly inderstood

permian

coleoptera-beetles

mecoptera-scorpionflies

neuroptera-lace wings

raphidioptera-snake flies

megaloptera-owl flies

land and sea

very rapid

causes not understoof

look like a combination

-anoxia, sea level change, vulcanism,ET

84%species go extinct

All Paleozoic Giants go extinct

many modern groups almost do

probably originated in the jurassic

first fossils=early cretaceous

Time

Associations

high levels of diversification

low levels of extinction-greater mobility=quick response to environmental change

lake indicators

watrer quality

water chemistry

water temperature

Beginning of Coevolution

Mutualism

an associations between two species that brings mutual benefit

ex.beetle-fungus,plant pollination,antaphid

one species being transported on te body of a larger species

an association in which one organism benefits and the other organism is unaffected

1. sloth and phoretic arthropods

phoretic mites drop down and lay eggs in dung

2. katydids and social wasps

leave at night and return at day

wasps protect katydids from predators

Specific

Guild evolution

Mutualistic Interactions

Plant-pollinator

yucca and yucca moth

bligate relationship

moth collect pollen from anthers

lays eggs into yucca ovaries

yucca gets pollinated, larvae have place to feed

relationship is obligate

long lived

specialized organs

aphids and bacterial symbionts

Hessian fly and Wheat

Herbivore-plant

fly larvae are stem borers of wheat

4 resistant alleles in wheat

4 matching alleles counter resistant varieties

reciprocal evolutionary change occuring among groups of species rather than pairs of species

plants and pollinators

predators adn herbivores

insects adn their fungal gardens

Evolved once in ants and termites

and 7 times in ambrosia beetles

the realtionships are obligate

However, farming insects can be found in association with different fungi species that belong within certain groups

Outcomes of coevolution

Cospeciation

correlated speciation of 2 associated lineages

as one group speciates so does the other

often called diversifying coevolution

to determine if this is the case, compare th ephylogenies of hoset and parasite/mutualist

ex. fig and fig wasps

obligate

matching phenologies

referref to interactions between plants and herbivorous insects

the evolution of novel defenses allows plants to diversify while their herbivores lag

escape and radiate

4 steps

1. a plant evolves a novel defense resulting in loss of its insect herbivores

2. free from herbivores, the plant radiates in to multiple species, all of which have the novel defense

3. eventual;y. a species of insect evolves the ability to use these plants

4. insects diversify into multiple species, each one specialized to use one of the new plant species

Insects as Herbivores

Feeding on plants

What are the major groups?

only 8 phytophagous orders

coleoptera, diptera,hemiptera, hymenoptera, lepidoptera,orthoptera,phasmida,thysanoptera

Phytophagy was a major evolutionary hurdle

50-57% of insects

400 MYA

plants evolved terrestrial forms

390 MYA

first terrestrial insecst

300 MYA

7 major orders of plant feeders present

Herbivorous insects can be classified by how they feed:

Chewers:

1.Surviving the microclimate of the plant(dry,windy,hot environment)

2. Holding on and penetrating the plant

claws

sticky pads

silk

mouthparts

3. DEaling with a suboptimal diet

adapting to feeding on plants

low in nitrogen and proteins

hight in indigestible cellulose

-process a lot of plant material

ex. grasshoppers

5 hrs to process meal

use of microrganisms,ex.aphids and buchnera

4. DEaling with plant defenses

physical and chemical defenses

Categorizing plant feeders

Monophagous

feed on one plant genus or a single species

ex.silkworms, box elder bug

feed on a number of plants usually in different genera within the same family

ex.most insect, monarch on various milkweeds

feed on plants in several plant families

ex.grasshoppers,gypsy moths

host plants generally available

mixed diests may be more balanced

easier to find host plants

multiple generations per year

reduce exposure to toxic compounds

1. Greater host use effieciency-insect plant interactions over evolutionary time

can more easily track the host(space and time)

can more easily digest and process hosts

can more easily detoxify plan chemical compounds

3. Predation- insect predator interactions over time

by specializing, insects increase their ability to hide form generalist predators adn to defend themselves

-crypsis, mimicry

chemical sequestration

3. Neural Limitations-because of their size, insects have a limited sensory systemand small brains o process information

Specialist will make decisions faster and be less error prone

Plants

Active Defenses

Physical Defenses

leaf toughness-some plants have a very tough leaves making it difficult for insects to initiate feeding

, spines, thornsmost effective against vertebrate herbivores, trichomes-tiny thorns or hairs that may contain nasty chemicals, detterent to both vertebrate and invertebrate herbivores

active defenses

chemical defenses

chemicals not required for basic maintence of plants

all plants have them

large variety in kinds and amounts

may not be plant-derived

do not deter specialist herbivores

secondary compound ex:

terpenoids

alkaloids

tannins

cyanogenic glycosides

irdoid glycosides

most common and diverse group

deter or attract insects complex with proteins stored in specialized cells some are essential oils

ex. eucalyptus, pinus

found in 20% of flowering plans

interfere with neural transmitters and enqymes, bitter taste

ex. caffeine, nicotine

widespread in plants

bind to and precipitate proteins, taste astringent

ex. fruit skins

found in 130 families

stored in vacuoles upondamage, release cyanide

ex. almonds

repellent to generalist insect herbivores, very bitter compounds

ex. olives, snapdragons

hiring bodyguards

ex.ant-accacia mutualism

plants get protection from herbivores and competitors

ants get food and shelter

Plants call for help

reduce future atack by attracting predators or parasatoids to remove herbivores

Passive Defenses

temporal avoidance