Phonotaxis in Insects

Phonotaxis is the movement of animals in response to sound vibrations especially

the sound vibrations in the ultrasound range. Even though human ear cannot

sense ultrasound, many animal species can produce and hear ultrasound. They

respond to certain frequencies of sound and show movements which may be

Positive Phonotaxis or Negative Phonotaxis. Positive Phonotaxis refers to the

movement of animals towards the source of sound waves of particular

frequencies and Negative Phonotaxis away from the sound.

Ultrasound

Sound is a form of electromagnetic energy produced by the mechanical vibration

and propagates through air in the form of waves. The air near the source of

mechanical vibration is compressed first which will create instability in the air

column resulting in the movement of air in the form of a wave. Sound is

measured in terms of Decibel and the frequency of wave propagation as Hertz.

The sound waves above 20 Hz and below 20 kHz lies in the audible range and

human can perceive only the audible portion of the sound waves. Sound waves

below 20 Hz are known as infrasonic sound and above 20 kHz is the Ultrasonic

sound. Human ear is not sensitive to infrasonic and ultrasonic sound vibrations

since human tympanum vibrates only to respond to sound vibrations within the

range of 20 Hz and 20 kHz.

Ultrasound wave

Ultrasound is a form of high frequency powerful wave that can travel along

straight lines even in the presence of obstacles. When ultrasound hits an object, it

bends and round and spread in all directions. Unlike ordinary sound waves,

ultrasound cannot pass through walls. So the range of wave propagation is limited

if there is an obstacle in front of the sound waves. But ultrasound will echo back if

the obstacle is large enough.

Ultrasound and Animals

Even though human ear cannot sense ultrasound, many animal species can

produce and hear ultrasound. Ultrasound presents two challenges for animals

that trying to hear it. First, high frequency waves translate to short wavelengths;

hearing organ must be miniaturized to match the wavelength. Second, high

frequency sounds tend to be supported by little energy. Not only do they

dissipate rapidly as the sound travels, making them relatively faint even close to

the source. They also are subject to absorption by hearing organ without being

transduced into a signal to the central nervous system.

In order to accommodate the lower energy of ultrasound, the hearing

membrane or tympanum, is typically thinner in animals which rely on ultrasound

for communication or navigation. The ear pinna of mammals which perceive high

frequency ultrasound may be quite complex. Bat ears are characterized by

grooves and channels which help to carry sounds to the tympanum, as well as

maintaining small differences in frequency (pitch) and amplitude (volume) which

can be used to localize sound sources.

Bat Echolocation

Ultrasonic signals are produced in two contexts. First in echolocation and

second in social contexts. Many animals like bat, rodents and insects like moths

use ultrasound frequencies for communication. Rodent pups use ultrasound to

call their mothers if they become isolated from her. Many species of insects can

produce and hear ultrasound of particular frequencies. Because bats prey on

insects, many insect species are attuned to bat echolocation calls and take evasive

measures if they hear bat call. Wax moths (Galleria mellonia) produce calling

songs to attract females and stop calling songs if a bat approaches.

Wax moth

Ultrasound frequencies ranging between 20 kHz and 100 kHz are used by

animals for communication and navigation. Many insect species respond to

ultrasound frequencies around 34 – 38 kHz. The acoustic startle / escape

response of insects is a phylogenetically wide spread behavioral act provoked by

an intense, unexpected sound. At least six orders of insects have evolved

tympanic ears that serve acoustic behavior that range from sexual communication

to predator detection.

Many insects, rodents, bats and other small mammals can hear ultrasound. Bats,

Dolphins and Whales utilize the ultra sound frequencies for echo location. They

have natural sonar systems to produce and receive ultrasound. Dogs can hear

ultrasound at the frequency range 16 kHz and 22 kHz. This property is utilized to

train dogs using ‘Dog Whistle ’. Rodents can hear ultrasound within the range of

32 kHz and 62 kHz. These high intensity sounds induce auditory stress in rodents.

Several types of fishes can detect ultrasound. Of the order Clupeiformes,

members of the subfamily Aloinae have been shown to be able to detect sounds

up to 180 kHz while the other sub families can hear only up to 4 kHz .

Dolphin Echolocation Whale Echolocation

Ultrasound and Insects

The acoustic startle / escape response is a phylogenetically wide spread

behavioral act, provoked by an intense unexpected sound. At least six orders of

insects have evolved tympanate ears that help to acoustic behavior that ranges

from sexual communication to predator detection. Insects that fly at night are

vulnerable to predation by insect eating animals. Insectivorous bats for example,

detect and locate their prey by using bisonar signals. Many nocturnal insects have

sensitive hearing structures to detect a range of ultrasonic frequencies from bats.

These insects respond to ultrasound by suddenly altering their flight showing

acoustic startle or negative phonotaxis. Under laboratory conditions, movement

and flight responses will be induced in insects exposed to specific frequencies of

ultrasound. Flight steering behavior like positive phonotaxis, negative phonotaxis

evasion etc will be elicited by appropriate combinations of ultrasound

frequencies. Some insects will be attracted (positive phonotaxis) towards the

source of ultrasound having frequencies between 5 kHz and 9 kHz. Negative

phonotaxis is found in nocturnal insects in response to ultrasound frequencies

ranging from 20 kHz and 44 kHz. Evasive or side-to-side steering during flight is

also found in response to high intensity (greater than 90 dB) ultrasound of 20 –

100 kHz.

Insects have well developed structures to produce and hear ultrasound vibrations.

There are evidences that ultrasound frequencies emitted by bats cause flying

moths to make evasive movements to escape from insect catching bat. The

steering movement of many species of crickets is based on ultrasound

frequencies at the range of 4 – 20 kHz. Cockroaches have ‘Sensory hairs’ which

are sensitive to ultrasound. The ‘anal cerci’ and ‘antennae’ of cockroaches have

ultrasound detecting sensory hairs. Spiders, wasps, beetles, flies etc have a

‘tympanic membrane’ to detect ultrasound. Cockroaches and house flies respond

to ultrasound frequencies within a range of 20 kHz and 38 kHz. Many insect

species communicate through ultrasound and social grouping and colony

maintenance utilize ultrasound frequencies. The wing movements of many insects

produce ultrasound to make communication among them.

Mosquitoes can produce and sense ultrasound vibrations around the

frequency 38 kHz. The male mosquito attracts females by emitting ultrasound

vibrations through the beating of wings. Female mosquito can hear ultrasound

through the sensory hairs on the antenna. After mating, female mosquito avoid

male and consider the males as their natural enemy and try to escape by sensing

the ultrasound from males.

Some studies on Phonotaxis

Steering response

The steering responses of field crickets Teleogryllus oceanius has been studied

using single tone pulses with carrier frequencies from 3 – 100 kHz . Three discrete

flight steering behaviors, positive phonotaxis, negative phonotaxis and evasion

were elicited by appropriate combinations of frequencies. Positive phonotaxis

was induced at 5 kHz and restricted to frequencies below 9 kHz. Negative

phonotactic steering similar to ‘early warning’ bat – avoidance behavior of moths

was produced by tone frequencies between 12 and 100 kHz. Evasive, side-to-side

steering was produced in response to high intensity ultrasound ranging between

20 – 100 kHz.

Field Cricket

Startle behavior

Studies conducted in bush crickets revealed that acoustic startle responses were

elicited for sound frequencies ranging from 25 to 60 kHz. No startle response was

observed below 10 kHz. Brodfuehrer in 1990 conducted experiments in flying

crickets to study the role of brain in evasive steering movements. In response to

ultrasonic stimuli, tethered flying crickets perform evasive steering movements

that are directed away from the sound source (negative phonotaxis) Ultrasonic

stimuli evoked descending activity in the cervical connectives both ipsilateral and

contra lateral to the sound source. Flight activity significantly increased the

amount of descending activity evoked by ultrasound. In crickets Teleogryllus

oceanius, the auditory interneuron, Omega neuron I responds to sounds over a

wide range of frequencies but is most sensitive to the frequencies 4.5 kHz.

Bush cricket

Avoidance response in Mosquito

Ultrasound of certain frequencies shows avoidance responses in mosquitoes.

Ultrasound ranging between 22 kHz and 44 kHz is found to be creating

acoustically hostile environment to mosquitoes. Mosquitoes can respond to

ultrasound using their bushy antennae. The wing beating of male mosquito

generates ultrasound in the range of 30 – 38 kHz.

Mosquito

Female mosquitoes consider male mosquitoes as their natural enemies after

mating and they try to avoid the presence of males. Studies conducted by Ludek

Zurek in two species of female mosquitoes, Anopheles quadrimaculatus and

Anopheles gambiae revealed that random ultrasonic frequencies ranging from 20

– 100 kHz can repel mosquitoes to a certain extent in laboratory conditions.

Evasive movement and negative phonotaxis was observed when the frequency of

ultrasound varied randomly.

Ultrasound and Cockroach

The repellency of ultrasound to female German cockroaches Blatella germanica

was studied in laboratory conditions using random ultrasound frequencies

ranging between 20 – 100 kHz. Under laboratory conditions, the response to

ultrasound in cockroaches was not so significant even though some members

showed unusual antennal movements in response to certain frequencies of

ultrasound.

Cockroach

Negative Phonotaxis in House fly

Negative phonotaxis in response to ultrasound was observed in houseflies.

Ultrasonic frequencies ranging between 22 – 44 kHz showed marked repellency in

houseflies. Group dispersion and negative phonotaxis was observed when the

houseflies were exposed to ultrasound pulsations of varying frequencies. Marked

DNA changes in housefly larvae were also observed after exposing them to

ultrasound for 48 hours. The genomic DNA of housefly larvae was extracted after

ultrasound induction, and the structures was analyzed by UV, fluorescence, IR and

III NMR. The 3’ end of Attacin gene was sequenced and compared by means of

PCR. All the results indicated that ultrasound induction can destroy the second

structure and the base stacking of genomic DNA of housefly larvae which will

result in mismatch repair during DNA duplication and finally change the sequence

of DNA.

House Fly

Pest control

Pest control using ultrasound is nowadays popular as an alternative way to avoid

environmental pollution through the accumulation of toxic chemicals and fumes.

These pest repellents create an ‘acoustically hostile environment’ to pests and

create stress on their nervous system. So they try to avoid the presence of

ultrasound by showing negative Phonotaxis.

Ultrasonic Pest repeller

D.Mohankumar