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.
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 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.
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.
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
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.
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.
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.
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.
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.
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