Behaviour etc

• nervous system

• sensory apparatus

• integration

• behaviour - processes and function

Nervous system

• insect nerve cells are complex

• insect nerve cells have highest metabolic rate of any known tissue

• insect nerve cells respond faster than ours (small size of ‘brain’)

• insect nerve cells can’t send long range pulses quickly

• insect nerve cells don’t have redundancy

organisation

• 2 ventral nerve chords + segmental ganglia

• CNS primitively ‘ladder’

• CNS has tendency to become fused

• ‘brain’ = supra- + suboesophageal ganglia

sense organs• mainly setae … many kinds of sensory

setae

• mechanosensory, chemosensory etc

• campaniform - cuticular stress

• placoid - chemoreception

• chordotonal organs - limb position

• equilibrium sensors (e.g. Johnson’s organ

vision

• ocelli

• stemmata

• compound eyes

• ocelli - late instar hemimetabolous insects, adult insects … fast response, some may detect images. Used in horizon detection, flight control

• stemmata - larvae of holometabolous insects. Largely light/dark detectors, limited image formation

• compound eyes - larvae of hemimetabolous insects, adult insects. Used to detect images

ommatidia organisation

• corneal lens

• crystaline cone - feeds light into rhabdomeres

• rhodopsins oriented in villi of rhabdomeres

• 3 colour (sometimes 4 colour) vision

• UV/blue/green, sometimes red

• detector cells twist, short (UV) cell detects polarization

apposition compound eyes

• commonest form in insects operating in daylight

• each ommatidium provides information from a narrow solid angle about its axis

• axes not oriented radially, some areas densely sampled by ommatidia arranged almost parallel (fovea)

• complex neural circuitry combines information from adjacent ommatidia

superposition compound eyes

• mainly nocturnal insects (& (modified) in butterflies)

• lens systems of many ommatidia act as little telescopes and generate an erect image on the ‘retina’ (made up of the packed detector elements of many ommatidia)

• eyes have a ‘clear space’ and produce ‘eye-shine’

• resolution not quite as good as apposition eye, light collection ~10-100x better

muscid eyes

• only found in muscoid flies (houseflies, blowflies, tachinids etc)

• apposition eyes BUT detector elements don’t twist AND detector elements from adjacent ommatidia that are ‘looking’ in the same direction are hooked up through a complex nerve mesh

• good light detection capability, good resolution• associated with need to collect photons to

compensate for effects of rapid turning flight

vision

• extensive neural processing in optic lobe,feature detection circuits similar to ours

• motion detection

• image detection

• speed of processing (flies have flicker-fusion thresholds > 5 x ours)

• insect vision is a field of very active research – and ANU is a world leader

• we now know insects are MUCH more capable than was thought the case even 10 years ago

• emulation of insect vision is proving a fertile field in robotic vision

• other insect senses are likely to prove equally ‘impressive’

behaviour

• navigation

• behaviour/ecology– development– maintenance– mating systems

navigation

• use of vision– landmarks … wasp, bee first flights– use of sun compass– use of polarization pattern if sun not visible– time clock to compensate for sun’s

apparent movement

• other senses - chemical, remembering steps

use of landmarks

• originally investigated in sphecid wasps• Philanthus work - Tinbergen• use of landmarks

– availability– kinds preferred– hierarchy of landmarks used at different

scales– hierarchy of ‘backups’ remembered

sun compass

• use position of sun in sky to navigate

• time clock to compensate for sun’s apparent movement (even overnight!)

• enables flight over long ranges or uniform habitat (ranges of kms)

• use of polarization pattern in small patches of clear sky if sun not visible

other senses

• chemical gradients

• magnetic sense

• remembering steps

• REAL navigation almost always involves a hierarchy of different senses, with backups

behaviour and ecology

• behaviour is a key process underlying ecology

• example we will take: ‘dragonfly life history’(will bounce around a range of species)

larval stages

• Diphlebia is the concrete example

• females lay eggs in rotten wood floating in pools

• micro-habitat of earliest larval stages unknown

• later stages occur under rocks in riffles

• emerge at night to hunt prey on rocks

adult maintenance

• thermoregulation– conformers– heliothermy– myothermy

• feeding– prey detection– interception

mating systems

• e.g. dragonflies (very well studied)

• ‘rendezvous’, operational sex ratio

• male behaviour

• sperm competition

• female responses to limit interference

• mating in dragonflies requires female action … males can hold on to encourage - but may lose opportunities

sperm competition

• Insects preadapted for strong sperm competition - sperm stored, only a few used per egg, eggs fertilized at laying

• displacement or extraction of previous sperm

• mate guarding to prevent take over by another male (with consequent loss of stored sperm)

exercise

• examination of dragonfly mating systems

References

• Physiology: Imms ‘Outlines of entomology’ as revised …CSIRO ‘Insects of Australia’

• Behaviour: navigation, mating systems/sperm competitionAlcock ‘Animal behavior: an evolutionary approach’

• dragonflies: Corbet ‘Dragonflies: behavior and ecology of Odonata’