brain (supraesophageal ganglion)

subesophageal ganglion (connected by circum-esophageal connectives)

ventral nerve chord

protocerebrum (visual)

deutocerebrum (antennae)

tritocerebrum (feeding)

coordination centers

respond to sensory info being received

may function without head and brain

taste and smell

chemical cues from external environment

chemosensilla are triggered by molecules

fire and give information

1. procurement of food

2. social insects

3. mate location

4. ID threats

5. suitable location for egg-laying

6. habitat selection

distance (olfaction)

contact (gustation)

general (common)

response to volatile molecules/ions in low concentrations

extremely sensitive

may show high specificity

contact with molecules or ions in chemical solution (dissolved in substrate)

high concentration

up to 5 neurons

less sensitive. Involved mostly in taste

respond to high concentration

sensilla less discriminating

escape/avoidance response

ammonia, chlorine, acid, etc.

molecules must contact receptor to elicit response

aquatic insects only contact dissolved chemicals

classification problems (insects with multiple types)

cone-like sensors

extend from body wall

both taste types

olfaction type

sunken cone in pit at body surface

allow access to molecules in both olfaction and contact

olfaction - many pores

contact - single pore on terminal end

touch

pressure

vibration

orientation

general movement

feeding

escape

reproduction (and others)

1. hair sensilla

2. campaniform sensilla

3. scolopophorous sensilla

single hair in socket

movement/bending triggers neurons

neuron below dome-like plate in cuticle

distortion/stretch/bend triggers neurons (movement of limbs, change in body position, etc.)

most complex

bundle of sensory neurons attach to body wall. 

sensitive to changes in movement, pressure, vibrations

widely distributed over body (subgenual organ, Johnston's organ, tympanal organ)

act by displacement

may come from external or internal environment

initiate series of nerve impulses

can be very high in frequency

mainly hair sensilla types

nerve impuleses depend on rate/deflection of hair

very acute. information acquired quickly

insect joints have hair sensilla

tell position of head, legs, antennae, mouthparts

knob-like reduced wings of diptera - important for balance and flight

gyrate very quickly and strained by change in direction

territoriality

mating

defense

thin stretched membrane with varying numbers of sensory cells for insect hearing

air spaces on both sides vibrate

vary in location on the body

highly developed

tympanal organs usually located on tibia

acoustic tranchea behind tympanal membrane

logitudinal slits (katydids) allow sound in, enhance detection of sound direction

typically form triangle on the head

able to integrate light over large field (accurate in terms of light sensitivity, but poor image resolution)

important for changes in light intensity. "horizon detectors" during flight

360-degree vision, high resolving power

ommatidia vary in number

retinula cells clustered, each with individual rhabdom

each ommatidia contributes part of the panoramic view

actual image consists of opposed points of light

different intensities at different points

severely limited light sensitivity (small diameter of individual ommatidia lenses)

specialized compound eye of nocturnal insects

ommatidia not separated by pigment. "clear zone allows neighboring ommatidia to communicate

(somtimes pigment present during day and fades at night)

reflective layer formed by small trachea

photon capture increase (gives light a second chance to stimulate retinula cells)

light reflected creates eye-shine

high in insects

allows them to see in "slow motion"

good for detecting motion

variation in molecular structure of visual pigments responsible for spectrum

most perceive UV (important for pollination)

Polarized light used for navigation and finding water

some harbor endosymbionts

others self-illuminate

different life stages/body parts/genders

green, yellow, white, red

main purpose = mating

cold light

Phengogidae

Drilidae

Lampyridae 

(flow worms, lightning bug, firefly, etc.)

basic unit of insect behavior

stimulation triggers specific muscle movment

may occur in groups resulting in coordinated group of movments important to survival

less stereotypic actions

ex) adjustments of walking/flying based on environment

networks that operate without stimulus or nervous system. 

Produce patterns

one of the complex insect behaviors

often interrupted and must be adjusted to situation

end result is same across species but process may differ

changes in how fast, or turn rate. No relation to direction source of stimulus

brings insect into favorable zones based on random movement

toward good away from bad

change in position/movement in response to source and direction and gradient of stimulus

(chemo, photo, etc. different mechanisms involved)

insect samples both sides of the environment

used at great distances

orientation by stimulus intensity

maintaining fixed angle from source

important for remaining right side up, or flying through complex landscapes

orientation upwind

used by flying insects because they have a hard time fixing on vlatile chemicals (patchy)

brings insect closer to the source

thousands of  miles, takes multiple generations

how does new generation know where to go?

positble time-compensated sun compass or geomagnetic cues

1. subgenual (all legs) 60 scolopidia

2. intermediate > forelegs 10-20 scolopidia

3. crista acoustica > forelegs scolopidia varies 

(basic unit = scolopidium)

1. neuroptera (lacewings)

2. coleoptera

3. mantodea

4. lepidoptera

5. orthoptera

immediate reaction to detection of ultrasound

(behavioral response to bats)

1. turn, fly directly away

2. oblique turn straight up

3. power dive (rapid drop with wings folded)

4. passive drop

5. complex looping dive

6. zig zag

7. land, remain still

most common method of sound production

file and scraper (teeth/pegs vibrate when rubbed against each other)

requires amplification (by environment or body)

ex) crickets/katydids

2nd method of sound production

muscles contract - bend tymbal membrane

muscles relax - tymbal retakes normal shape

produce variety of sounds

ex) cicadas

produces ultrasound in certain moths

1. communication

2. interfere with bat sonar

3. mimic bats

4. warn bats of distaste

high frequency wing beat produces sounds

tone is species specific, varies with age, temperature, sexual receptivity

development of Johnston's organ allows insects to hear others

photoreceptive structure

consists of retinula (nerve cells) and closely packed microvilli

light falling onto rhabdom changes configuration of neuron

travels as signal to brain

stemmata (larval or lateral ocelli)

frontal or dorsal ocelli (nymphs, some adults)

compound eyes

only visual organ of larvae

located on head, vary in number

each has numerous nerve cells

point in different directions

respond to high light intensity, low resolving power

the motivational state

governs behavior based on internal and external environment

ability to learn based on inheritance/environment

internal factors 

1. rhythms

2. Inhibitory feedback

3. Long-term physiological changes

patterns and cycles (active/inactive phases)

diel rhythm - maintained by biological clock, reset by light and dark

circadian rhythm - aout 24 hours

temporal physiological change in responsiveness

ex)when hungry, eat, when full, stop

(in blow flies)

labellum automatically extends toward sugars when crop is empty. blocked when crop is full

often the result of development and molting

ex) adults don't develop sexual behavior until hormone levels increased

principle function is for reproduction, metamorphosis, and growth

some are similar to vertebrate hormones

brain hromone

produced by prothoracic glands

important for growth and molting, caste determination, and breaking diapause

important for development, molting, sexual reproduction

inhibits metamorphosis in young. levels drop with age

regulates activity of accessory glands, pheromones and sexual behavior

substances closely related to JH. found in some plants

may inhibit metamorphosis

used in insect growth regulator insecticides (IGR)

egg laying (most insects)

rapid fertilization

controlled by hormones in the brain and directly by the nervous system

process of expelling eggs from body into environment

controlled directly by nervous system

little to no parental care

vary in size .2-13mm

lots of yolk, no maternal nutrition provided

rapid development begins at fertilization

allows entry of sperm during fertilization in oviduct

fairly elastic (egg squeezed through ovipositor tube)

protects embryo

allows gas exchange

additional layer of protection

allows attachment of eggs to surfaces

colleterial glands

case-like structure that protects a group of thin-shelled eggs

colleterial glands

development inside the mother. live birth

advantage = protection. shorter life cycle (faster development)

egg with very little yolk

mother transfers nutrients through placenta-like tissue 

no oral feeding (only absorption)

larvaposition

embryo lives in hemolymph and takes up nutrients

in some cases larvae parasitize other insects or consume the mother

hatch within the mother

oral feeding from secretions of the mother. feed only 1 or a few at a time

deposit full-grown larvae and ready to pupate

molting. replacing old cuticle with new larger one

portion of the old cuticle is digested

molt includes tracheal linings, foregut, hindgut lining, and certain structures of the endoskeleton

cast off cuticle after molting (the molt)

usually retains the shape of the insect

prothoracicotropic hormone

hormone that triggers intial stages of the molting cycle

stimulates the prothoracic glands (molting glands)

secreted from epidermal cells

contains enzymes that digest old cuticle

ecdysis triggering hormone

triggers molting when new skeleton forms under the old one

splits along weakness line - the midline of dorsal side thorax 

rupturing force is pressure of the hemolymph and contraction of muscles

takes in air or water to stetch body to appropriate size

hemolymph forced into wing veins for unfolding of wings

4-8 in most insects

10-12 in some odonata

up to 28 in mayflies

stages between each molt

1st is between hatching and first larval molt

2nd is between 1st and 2nd molt

wings (if any) develop externally during immature stages

ordinarily no quiescent stage

3 types of change occur within simple metamorphosis

wings develop internally

quiescent pupal stage precedes last molt, in which the insect doesn't feed and most change occurs

2 processes: histolysis and histogenesis

larval structures break down into material used in developing adult stages

(part of complete metamorphosis)

epidermal thickenings beneath larval cuticle

develop into wings and legs

(complete metamorphosis)

young of simple metamorphosis types

appear very similar to adults

have compound eyes and wings start as buds that increase in size over time

1st type of change in simple metamorphosis

wingless as adults, slow progression in size

2nd type of change in simple metamorphosis

"gradual" metamorphosis to winged adults. Nymphs and adults share the same habitat

3rd type of change in simple metamorphosis

gilled, aquatic nymphs, different from adults

young called naiads

follows the last larval instar in complete metamorphosis

usually covered in a cocoon, or some other protective material

survive winter this way

go through complete metamorphosis

wingless larvae, pupa, winged adults

young do not share same habits/habitat as adults