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Major categories of Sense Organs

1. Mechanoreceptors (movement: tactation, proprioception, and hearing)• Trichoid sensilla

• Placoid sensilla

• Campaniform sensilla

• Chordotonal sensilla

2. Chemoreceptors (chemicals: substrate & airborne)• Trichoid sensilla

• Cone or Basicone (basiconic) peg sensilla

• Coeloconic peg sensilla

• Sensory pits

3. Photoreceptors (photons: light and heat)

4. Less common types:• Thermoreceptors (temperature: e.g., mammalian parasites)

• Hygroreceptors (humidity: e.g., some beetles, lice)

• Magnetoreceptors (magnetic fields: e.g., bees)

cuticleepidermis

scolopale

base of seta

vacuole

tormogencell

trichogen cellsense cellaxon

axon bundle

sense cells

tormogen cell

scolopalemembrane

scolopaledendrite

tormogen cell

sensecell

cuticle

thickened barouter lamella

inner lamella

epid.

attachmentor cap cell

scolopale rod

scolopale orenvelope cell

fibrous sheath cell(not always present)

neuron

glial cell

scolopale cap

CHORDOTONAL SENSILLUM

CAMPANIFORM SENSILLUM

PLACOID SENSILLUM

TRICHOID SENSILLUM Mechanoreceptors

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Trichoid sensilla from Anopheles mosquito antenna(tactation)

Placoid sensillaon honey beeflagellomeres

(tactation)

flagellum

scape

pedicel

1 mm

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Campaniform sensilla(cockroach leg: proprioception)

HAIR PLATES or HAIR BEDS

mat of trichoid sensilla

hardened cuticlemembrane

axons

sense cells(neurons)

scolopale(envelope)

cellcap cell

accessorycell

cuticleepidermis

scolopale

tympanal membrane

cap cell

fibrous sheath cell

axon bundle

neuron(sense

cell)

SUBGENUAL ORGAN

TYMPANAL ORGAN

JOHNSTON’S ORGAN

flagellum STRETCH RECEPTOR

axonnerve axons

pedicelouter ring ofscolopidia

inner ring ofscolopidia

scapeaxon bundles

nerve cell body multi-polar

neuron muscle

Chordotonalsensilla

(mostly, hearing)

(proprioception)

(proprioception)

scolopale cells

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Hair plates: left prosternal organ in a mantis(Dictyoptera: Mantodea -- proprioception)

base of head

prosternal organ

neck sclerites

Joe Singleton 2001

Johnston’s organ – whirligig beetles(Coleoptera: Gyrinidae -- tactation)

water surface

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Johnston’s organ – mosquitoes(Diptera: Culicidae -- hearing)

Male starts, then matches female frequency (Gibson & Russell 2006)

Tympanal organs (Orthopteroid insects – hearing)

cap cells

sensoryneurons

katydid ear(Tettigoniidae)

mantis ear(ultrasound)(Mantidae)

grasshopper ear(Acrididae)

scolopale cells

tympanum

tympanal membrane

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More tympanal organs (Cicadidae)

(approx. 1500 chordotonal sensilla per tympanum)

male

X

Y

More tympanal organs (Lepidoptera: bat detection )

Night-flying butterfly,Hedylidae: at base of

wing (ultrasound)

Night-flying moth, Noctuidae:rear of thorax (ultrasound)

right ear

TWOchordotonal

sensilla

tympanalmembrane

B cell

A1 & A2

tracheal sac tracheal sac

tracheal sac

trachealsac

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More tympanal organs(Chrysopidae: bat detection )

scolopidia(≈ 25)

tympanalmembrane

swelling

Lee Miller, 1970, ‘71, ‘75

Tympanal organ

accessory & cap cells

(to wing tip)

C

(to wing tip)

pegopenings in cuticle

cuticle

scolopale

vacuoletormogen cell

epidermis

trichogen cell

axon bundlesensory neurons

branching dendrites

opening in cuticle opening (peg)

peg

vacuole

sensory neurons

epidermis

tormogencell

scolopale

axon bundlescolopale

neurons &supporting cells

opening

sensorypeg

trichogen cell

Chemoreceptors

COELOCONIC PEG

TRICHOIDSENSILLUM(hole in tip)

BASICONIC PEG(thin-walled)

SENSORY PIT(found in all insects)

>30,000 in Apidae!

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Basiconic peg sensilla

Anopheles mosquito antenna

Heliothismoth

haustellum

Coeloconic peg from Anopheles mosquito antenna

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Male moth antennae: the gold standard for olfaction

> 70,000 olfactory sensors

Trail-followingin ants:

another olfactorytour de force

An Old World army ant, Aenictus sp.

More than 40 glands secrete complexes of

chemicals in ants.

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The insect visual sense: PhotoreceptionLight: Visible, IR, UV (different λ’s)

Major categories ofvisual sense organs

1. Dermal receptors (simple epidermal cells)• many larval insects

• all stages of cockroaches

• in cephalopharyngeal skeleton of muscoid maggots

2. Dorsal ocelli (“true ocelli”)• 4 (ancestor) 3 (middle one can be “bilobed”) 2 0

• …or 2 (ancestor) 3 (Crustacea + Insecta) 2 0

• can’t form an image

• fast response time; responds to very low levels of light

3. Stemmata (“lateral ocelli”)• larvae of just about all Hemimetabola (Endopterygota)

• capable of forming an image (but may not use it)

4. Compound eyes (multi-faceted)• Not in larval Hemimetabola

• primary visual sense organs of insects

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Dorsal Ocellus

Dorsal (true) ocelli – damselfly (Odonata: Zygoptera)

lens

retinal apparatus

Simple eyes: stemmata (“lateral ocelli”) – larvae of Lepidoptera

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epidermis

DORSAL OCELLUS

corneal lenscorneagen cells

cuticle

pigment cells

pigment cell

rhabdomretinula cell

ocellar nerveto protocerebrum

retinula (sense) cell

corneal lens

cuticle

epidermis

retinula cells

rhabdompigment

corneagen cellscrystalline cone (lens)

ocellar nerveto protocerebrum

ocellar nerve (optic nerve)

STEMMA(“lateral ocellus”)

cross-section of retinal apparatus