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