Neuroethology:Sound in insects

http://biolpc22.york.ac.uk/404/

References

Young, D (1989) Nerve cells and animal behaviour CUP [1st edition, chapter 7]

Also, chapters in: Carew Behavioral neurobiology Zupanc Behavioral neurobiology

papers are on the webhttp://biolpc22.york.ac.uk/404/cjhe/cricket_singing/insect.htm

What is neuroethology?

approach to analyse neural function in terms of evolutionary advantage

Main points of lecture

Sound transmission is inefficient Insects use sound in a major way Overcoming physical obstacles Modifying

wings for sound production the environment for sound production cuticle to hear

Private communication

About sound

sound is a wave of particle compression and rarefaction

energy (or power) is transferred from sender to hearer

sound gets quieter further away sound has to be discriminated according

to species, context and from random noise

Sound properties

speed c (330 m s-1) wavelength (m) frequency f (Hz, cycles/s)

for 330Hz, wavelength 1m for 3.3kHz, wavelength 0.1m for 33kHz, wavelength 0.01m =

10mm

fc

Power transfer - i

First problem for an insect - for air/water interface about 0.02%

Power transfer - ii

Usually other insect far away -

With distance, power decreases

more bad news for insects!

2

1

d

Power transfer - iii

Usually insects small - sound emitted is dependent

on ratio of insect size / wavelength of sound

Power transfer - iv

if you are smaller than 0.2 * more bad news!

Insects use sound in a major way

Mantids* Grasshoppers/crickets* bugs* beetles* diptera (true flies)* lacewings moths

How do they manage this if physics is so unfavourable?

Overcoming physical obstacles

Resonance Baffle Horn

Sound production Sound reception

Resonance

Mass and a spring; resonant frequency

s is stiffness, m mass below fo in phase; at fo 90o; above fo out

of phase

m

sfo

2

1

Gryllus

Field cricket nice loud

song, carries a long way

attracts females & males

territorial

Gryllus

EMGs

sound

oscillogram

sonogram

Females…

… walk to the loudest sound

Sound made by wing

plectrum

add wax to harp

frequency reduced resonator affected

remove teeth

Gryllus campestris

sound output 60 W muscle work 2 mW efficiency 3%

Can they do any better?

Bush crickets

Higher frequency damped oscillation

Baffle

Bush cricket Oecanthus power *

12

Gryllotalpa

mole cricket

Horn shaped burrow

Gryllotalpa

sound output 1 mW muscle work 5 mW efficiency 20%

Summary so far

Modified wings for sound production Modifying the environment for sound

production

Well done the male crickets!Now onto: what about hearing?

Hearing

locust = grasshopper ears

Tympanum structure

Tympanum structure

Muller’s organ has sensory endings in it

Tympanum (ear drum) taut membrane

side view

top view

Movement

it’s the relative movement which will stretch the axons

Movement

peaks at 3 & 6kHz indicate resonance resonance also shown by phase plot folded body not in phase with membrane

even when at 4kHz amplitude is same relative movement needed to stretch

axons of Muller’s organ

Cricket hearing

acoustic trachea acts like horn for 5kHz sound

Summary so far: Resonance!!

Modified wings for sound production Modifying the environment for sound

production Modified cuticle to hear

Now onto: shh, let’ keep this to ourselves?

Drosophila courtship

Male has black tip

Olfaction

Singing

Detecting vibration

near field sound movement detector aristae - bristles on

antennae

Private communication

Sound movement in dB

since sound is measured on a log scale, 80 << 95

Summary

The neuroethological approach relates the function of the nervous system to its evolutionary advantage

Many insects use sound produce it quite efficiently hear it effectively