Integration time for short broad band clicks in echolocating FM-bats (Eptesicus fuscus)

Vespertilionid FM-bats (four Eptesicus fuscus and one Vespertilio murinus) were trained in an electronic phantom target simulator to detect synthetic echoes consisting of either one or two clicks. The threshold sound pressure for single clicks was around 47 dB peSPL for all five bats corresponding to a threshold energy of -95 dB re 1 Pa² * s. By varying the interclick interval, T, for double clicks it was shown that the threshold intensity was around — 3 dB relative to the threshold for single clicks at T up to 2.4 ms, indicating perfect power summation of both clicks. A threshold shift of -13.5 dB for a 1 ms train of 20 clicks (0.05 ms interclick interval) confirmed that the bats integrated the power of the stimuli. At T longer than around 2.5 ms the threshold for double clicks was the same as for single clicks. Thus, the bats performed like perfect energy detectors with an integration time of approximately 2.4 ms. This integration time is an order of magnitude shorter than that reported for bats listening passively for pure tones. In our setup the bats emitted sonar signals with durations of 2–3 ms. Hence, the results may indicate that while echolocating the bats integration time is adapted to the duration of the sonar emissions.Abbreviations AGC automatic gain control - FM frequency modulated - peSPL peak equivalent sound pressure level - rms root mean square - SD standard deviation - SE standard error of mean - T interclick interval     

Effects of Temperature on Auditory Sensitivity in Eurythermal Fishes: Common Carp Cyprinus carpio (Family Cyprinidae) versus Wels Catfish Silurus glanis (Family Siluridae)

Background

In ectothermal animals such as fish, -temperature affects physiological and metabolic processes. This includes sensory organs such as the auditory system. The reported effects of temperature on hearing in eurythermal otophysines are contradictory. We therefore investigated the effect on the auditory system in species representing two different orders.

Methodology/Principal Findings

Hearing sensitivity was determined using the auditory evoked potentials (AEP) recording technique. Auditory sensitivity and latency in response to clicks were measured in the common carp Cyprinus carpio (order Cypriniformes) and the Wels catfish Silurus glanis (order Siluriformes) after acclimating fish for at least three weeks to two different water temperatures (15°C, 25°C and again 15°C). Hearing sensitivity increased with temperature in both species. Best hearing was detected between 0.3 and 1 kHz at both temperatures. The maximum increase occurred at 0.8 kHz (7.8 dB) in C. carpio and at 0.5 kHz (10.3 dB) in S. glanis. The improvement differed between species and was in particular more pronounced in the catfish at 4 kHz. The latency in response to single clicks was measured from the onset of the sound stimulus to the most constant positive peak of the AEP. The latency decreased at the higher temperature in both species by 0.37 ms on average.

Conclusions/Significance

The current study shows that higher temperature improves hearing (lower thresholds, shorter latencies) in eurythermal species from different orders of otophysines. Differences in threshold shifts between eurythermal species seem to reflect differences in absolute sensitivity at higher frequencies and they furthermore indicate differences to stenothermal (tropical) species.     

Wing-Click Sounds of Heliconius cydno alithea (Nymphalidae: Heliconiinae) Butterflies

Field-collected Heliconius cydno Doubleday females were observed producing audible wing clicks during encounters between conspecifics in greenhouses in a large insectary during the day and at roosting time. Occasionally, these females also were observed producing sounds in aggressive encounters with females of a close relative, H. erato (L). However, the wing-clicks were not observed subsequently from first-generation adults born in the greenhouses. The sounds were produced in short trains of 3–10 wing-clicks at the rate of 10 clicks/s. The individual clicks had a mean duration of 1.48 ms and a broad frequency spectrum, with a peak near 1075 Hz. This peak lies near the 1200-Hz frequency of maximal sensitivity measured previously for auditory neurons of H. erato. The production of these previously unreported sounds suggests that wing clicks may play a role in both intra- and interspecific communication among Heliconius species.     

Gap detection in the starling (Sturnus vulgaris)

Summary Gap-detection thresholds of single units were determined from auditory forebrain neurons of the awake starling. Nine different response types were statistically defined from the discharge pattern to a 400 ms broadband noise stimulus. The gap stimuli consisted of two broadband noise bursts which were separated by a gap ranging from 0.4 to 204.8 ms duration. The median minimumdetectable gap for 121 out of 145 units that had a significant threshold 204.8ms was 12.8 ms; 20% of the neurons showed thresholds between 0.4 and 3.2 ms. The neurons of the nine response types differed significantly in their minimum-detectable gaps; neurons with phasic-tonic and phasic excitation exhibited the best (i.e. shortest) minimum-detectable gaps. The neurons of the three different recording areas (field L, NCM and HV) were significantly different in their minimumdetectable gaps; field L neurons showed the best temporal resolution for gaps in broadband noise. Gap-detection thresholds are compared with psychophysical thresholds determined with the same stimuli and the relevance of forebrain units for temporal resolution is discussed.Abbreviations CS control stimulus - HV hyperstriatum ventrale - HVc hyperstriatum ventrale pars caudalis - NB noise burst - NCM neostriatum caudale pars medialis - NS noise stimulus - SGS standard gap series - TW time window     

Arctiid moth clicks can degrade the accuracy of range difference discrimination in echolocating big brown bats,Eptesicus fuscus

Summary Four big brown bats (Eptesicus fuscus) born and raised in captivity were trained using the Yes/No psychophysical method to report whether a virtual sonar target was at a standard distance or not. At threshold bats were able to detect a minimum range difference of 6 mm (a t of 36 s).Following threshold determinations, a click burst 1.8 ms long containing 5 pulses from the ruby tiger moth, Phragmatobia fuliginosa (Arctiidae), was presented randomly after each phantom echo. The sound energy of the click burst was -4 dB relative to that of the phantom echo. Clicks presented for the very first time could startle naive bats to different degrees depending on the individual.The bats' performance deteriorated by as much as 4000% when the click burst started within a window of about 1.5 ms before the phantom echo (Fig. 4). Even when one of ten phantom echoes was preceded by a click burst, the range difference discrimination worsened by 200% (Fig. 9). Hence, clicks falling within the 1.5 ms time window seem to interfere with the bat's neural timing mechanism.The clicks of arctiid moths appear to serve 3 functions: they can startle naive bats, interfere with range difference determinations, or they can signal the moth's distastefulness, as shown in earlier studies.Abbreviations peSPL peak equivalent sound pressure level - sd standard deviation - FM frequency modulation - CF constant frequency - EPROM erasable programmable read only memory     

Comparative collicular tonotopy in two bat species adapted to movement detection,Hipposideros speoris andMegaderma lyra

Summary The tonotopic organization of the inferior colliculus (IC) in two echolocating bats,Hipposideros speoris andMegaderma lyra, was studied by multiunit recordings.InHipposideros speoris frequencies below the range of the echolocation signals (i.e. below 120 kHz) are compressed into a dorsolateral cap about 400–600 m thick. Within this region, neuronal sheets of about 4–5 m thickness represent a 1 kHz-band.In contrast, the frequencies of the echolocation signals (120–140 kHz) are overrepresented and occupy the central and ventral parts of the IC (Fig. 3). In this region, neuronal sheets of about 80 m thickness represent a 1 kHz-band. The largest 1 kHz-slabs (400–600 m) represent frequencies of the pure tone components of the echolocation signals (130–140 kHz).The frequency of the pure tone echolocation component is specific for any given individual and always part of the overrepresented frequency range but did not necessarily coincide with the BF of the thickest isofrequency slab. Thus hipposiderid bats have an auditory fovea (Fig. 10).In the IC ofMegaderma lyra the complete range of audible frequencies, from a few kHz to 110 kHz, is represented in fairly equal proportions (Fig. 7). On the average, a neuronal sheet of 30 m thickness is dedicated to a 1 kHz-band, however, frequencies below 20 kHz, i.e. below the range of the echolocation signals, are overrepresented.Audiograms based on thresholds determined from multiunit recordings demonstrate the specific sensitivities of the two bat species. InHipposideros speoris the audiogram shows two sensitivity peaks, one in the nonecholocating frequency range (10–60 kHz) and one within the auditory fovea for echolocation (130–140 kHz).Megaderma lyra has extreme sensitivity between 15–20 kHz, with thresholds as low as –24 dB SPL, and a second sensitivity peak at 50 kHz (Fig. 8).InMegaderma lyra, as in common laboratory mammals, Q_10dB-values of single units do not exceed 30, whereas inHipposideros speoris units with BFs within the auditory fovea reach Q_10dB-values of up to 130.InMegaderma lyra, many single units and multiunit clusters with BFs below 30 kHz show upper thresholds of 40–50 dB SPL and respond most vigorously to sound intensities below 30 dB SPL (Fig. 9). Many of these units respond preferentially or exclusively to noise. These features are interpreted as adaptations to detection of prey-generated noises.The two different tonotopic arrangements (compare Figs. 3 and 7) in the ICs of the two species are correlated with their different foraging behaviours. It is suggested that pure tone echolocation and auditory foveae are primarily adaptations to echo clutter rejection for species foraging on the wing close to vegetation.Abbreviations BF Best frequency - CF constant frequency - FM frequency modulated - IC inferior colliculus - HS Hipposideros speoris     

Effects of Boat Engine Noise on the Auditory Sensitivity of the Fathead Minnow, Pimephales promelas

Fishes are constantly exposed to various sources of noise in their underwater acoustic environment. Many of these sounds are from anthropogenic sources, especially engines of boats. Noise generated from a small boat with a 55 horsepower outboard motor was played back to fathead minnows, Pimephales promelas, for 2 h at 142 dB (re: 1 Pa), and auditory thresholds were measured using the auditory brainstem response (ABR) technique. The results demonstrate that boat engine noise significantly elevate a fish's auditory threshold at 1 kHz (7.8 dB), 1.5 kHz (13.5 dB), and 2.0 kHz (10.5 dB), the most sensitive hearing range of this species. Such a short duration of noise exposure leads to significant changes in hearing capability, and implies that man-made noise generated from boat engines can have far reaching environmental impacts on fishes.     

Temporal coding in the auditory receptor of the moth ear

Temporal coding in the moth ear was inferred from the response of the auditory receptor to acoustic stimuli with different temporal characteristics.

Androgen-induced alterations in vocalizations of femaleXenopus laevis: modifiability and constraints

Summary We examined effects of exogenous androgen (testosterone and dihydrotestosterone) on vocalizations of ovariectomized, adult female South African clawed frogs,Xenopus laevis. When paired with sexually active males, all ovariectomized females exhibited ticking, the unreceptive or release call. Ticking consists of low amplitude, regularly spaced clicks with a mean interclick interval of 154 ms. When androgen-treated and paired with sexually active males, these ovariectomized females also exhibited an aberrant call (atypical ticking) in which click multiples replaced the single clicks of ticking. Mean ICI's for atypical ticking were 37 ms for click doublets and 22 ms for click quadruplets. Androgen treatment decreased the total time spent vocalizing (typical and atypical ticking) by ovariectomized females.All androgen-treated females were then tested repeatedly with sexually receptive females in an attempt to elicit the male-typical vocalization, mate calling. Six of 17 females did not vocalize at all, even when gonadotropin injected. Eight females gave rapid (mean ICI, 36 ms) trains of clicks in an irregular temporal pattern (tick-like calls). Three females gave brief trills with alternating fast and slow components. Comparison of mate calllike vocalizations of androgen-treated females to mate calling of males reveals that calls in females are considerably shorter in duration (female: 0.32 min versus male: 45 min) and slower in tempo (ICI's; fast trill, female: 21 ms, male: 14 ms; slow trill, female: 36 ms, male: 28 ms). Incomplete masculinization of the vocal pattern of females by androgen treatment in adulthood may be due to developmental constraints on the modifiability of the neurons and muscles responsible for calling.Abbreviations C cholesterol - DHT dihydrotestosterone - HCG human chorionic gonadotropin - IBI interburst interval - ICI interclick interval - ovx ovariectomized - T testosterone     

Acoustic intensity discrimination by the cichlid fish Astronotus ocellatus (Cuvier)

The acoustic intensity discrimination ability of the oscar (Astronotus ocellatus), a cichlid fish, was investigated using an automated positive reward method. Intensity discrimination thresholds (I, in dB) for 7-s continuous pure tone signals were measured both as functions of sound intensity above thresholds, i.e., sensation levels, (SL)(+10 dB, +20 dB and +30 dB) and frequency (200 Hz, 500 Hz, and 800 Hz). I at 500 Hz for +10 dB, +20 dB, and +30 dB SLs are 8.9, 5.5, and 3.3 dB, respectively. I (at+20 dB SL) for 200 Hz, 500 Hz, and 800 Hz are 4.5, 5.5, and 9.3 dB, respectively. Despite having poor auditory sensitivity (narrow frequency range and high thresholds), the intensity discrimination ability of the oscar follows the general trends of previously studied fish species, however, with higher thresholds.     

Evoked potentials of the auditory cortex of the porpoise,Phocoena phocoena

Summary Evoked potential (EP) recordings in the auditory cortex of the porpoise,Phocoena phocoena, were used to obtain data characterizing the auditory perception of this dolphin. The frequency threshold curves showed that the lowest EP thresholds were within 120–130 kHz. An additional sensitivity peak was observed between 20 and 30 kHz. The minimal EP threshold to noise burst was 3·10^–4–10^/s-3 Pa. The threshold for response to modulations in sound intensity was below 0.5 dB and about 0.1% for frequency modulations. Special attention was paid to the dependence of the auditory cortex EP on the temporal parameters of the acoustic stimuli: sound burst duration, rise time, and repetition rate. The data indicate that the porpoise auditory cortex is adapted to detect ultrasonic, brief, fast rising, and closely spaced sounds like echolocating clicks.Abbreviation EP evoked potential     

Auditory brain stem responses in characterization of dolphin hearing

Summary Auditory brain stem responses (ABR) were recorded from the head surface of non-anesthetized and non-relaxed bottle-nosed dolphins, Tursiops truncatus. The region of best ABR recording was shown to be located 6–9 cm caudal to the blowhole. The threshold values were about 1 mPa for noise bursts and –3 dB re 1 mPa for tone bursts of the optimal frequency (80 kHz). The maximum frequency at which ABR could be evoked was 140 kHz. The duration of temporal summation reached 0.5 ms at intensities near the threshold and decreased with an increase in intensity. When the stimuli were paired clicks of the same intensity, the time to complete recovery from the second response was about 5 ms, while that to its 50% recovery was 0.7 ms. When the conditioning click exceeded the testing one in intensity, prolongation of the recovery period was observed. A 40-dB intensity difference led to an approximately 10-fold prolongation of this period.Abbreviations ABR auditory brain stem response - EP evoked potential     

The detection of phantom targets in noise by serotine bats; negative evidence for the coherent receiver

Summary Using a target simulator three serotine bats,Eptesicus serotinus, were trained to judge whether a phantom target was present or absent. The echolocation sounds emitted by the bats during the detection were intercepted by a microphone, amplified and returned by a loudspeaker as an artificial echo, with a delay of 3.2 ms and a sound level determined by the overall gain and cry amplitude. The cry level of each pulse was measured and the echo level received by the bat was calculated. The target was presented in 50% of the trials and the gain adjusted using conventional up/down procedures. Under these conditions between 40 and 48 dB peSPL were required for 50% detection (Figs. 2, 3).In a subsequent experiment the phantom target was masked with white noise (N_o) with a spectrum level of –113 dB re. 1 Pa·Hz^–1/2. The thresholds were increased by 7–14 dB. Energy density (S) of a single pulse was measured and used to estimate S/N_o, which ranged from 36–49 dB at threshold. Theoretically the coherent receiver model predicts the ratio between hits and false alarms observed for the bats at a S/N_o of ca. 1–2 dB. Since the bats require 40–50 dB higher S/N_o (Fig. 3), this is taken as negative evidence for coherent reception (cross correlation).Furthermore, a strong sensitivity to clutter was found since there seemed to exist a fixed relationship between thresholds and clutter level.Abbreviations C clutter - Nbw noise in a specified bandwidth - No noise in i Hz bandwidth - peSPL peak equivalent sound pressure level - S signal energy - SD standard deviation - Y/N Yes/No psychometry - 2AFC two alternative forced choice psychometry     

Hearing in Cichlid Fishes under Noise Conditions

Background

Hearing thresholds of fishes are typically acquired under laboratory conditions. This does not reflect the situation in natural habitats, where ambient noise may mask their hearing sensitivities. In the current study we investigate hearing in terms of sound pressure (SPL) and particle acceleration levels (PAL) of two cichlid species within the naturally occurring range of noise levels. This enabled us to determine whether species with and without hearing specializations are differently affected by noise.

Methodology/Principal Findings

We investigated auditory sensitivities in the orange chromide Etroplus maculatus, which possesses anterior swim bladder extensions, and the slender lionhead cichlid Steatocranus tinanti, in which the swim bladder is much smaller and lacks extensions. E. maculatus was tested between 0.2 and 3kHz and S. tinanti between 0.1 and 0.5 kHz using the auditory evoked potential (AEP) recording technique. In both species, SPL and PAL audiograms were determined in the presence of quiet laboratory conditions (baseline) and continuous white noise of 110 and 130 dB RMS. Baseline thresholds showed greatest hearing sensitivity around 0.5 kHz (SPL) and 0.2 kHz (PAL) in E. maculatus and 0.2 kHz in S. tinanti. White noise of 110 dB elevated the thresholds by 0–11 dB (SPL) and 7–11 dB (PAL) in E. maculatus and by 1–2 dB (SPL) and by 1–4 dB (PAL) in S. tinanti. White noise of 130 dB elevated hearing thresholds by 13–29 dB (SPL) and 26–32 dB (PAL) in E. maculatus and 6–16 dB (SPL) and 6–19 dB (PAL) in S. tinanti.

Conclusions

Our data showed for the first time for SPL and PAL thresholds that the specialized species was masked by different noise regimes at almost all frequencies, whereas the non-specialized species was much less affected. This indicates that noise can limit sound detection and acoustic orientation differently within a single fish family.     

Hearing and evasive behaviour in the greater wax moth, Galleria mellonella (Pyralidae)

Greater wax moths (Galleria mellonella L., Pyraloidea) use ultrasound sensitive ears to detect clicking conspecifics and echolocating bats. Pyralid ears have four sensory cells, A_1?4. The audiogram of G. mellonella has best frequency at 60 kHz with a threshold around 47 dB sound pressure level. A₁ and A₂ have almost equal thresholds in contrast to noctuids and geometrids. A₃ responds at + 12 to + 16 dB relative to the A₁ threshold. The threshold data from the A‐cells give no indication of frequency discrimination in greater wax moths. Tethered greater wax moths respond to ultrasound with short‐latency cessation of flight at + 20 to + 25 dB relative to the A₁ threshold. The behavioural threshold curve parallels the audiogram, thus further corroborating the lack of frequency discrimination. Hence, the distinction between bats and conspecifics is probably based on temporal cues. At a constant duty cycle (percentage of time where sound is on) the pulse repetition rate has no effect on the threshold for flight cessation, but stimulus duration affects both sensory and behavioural thresholds. The maximum integration time is essentially the same: 45 ms for the A₁‐cell and 50–60 ms for the flight cessation response. However, the slopes of the time‐intensity trade‐off functions are very different: ? 2.1 dB per doubling of sound duration for the A₁‐cell threshold, and ? 7.2 dB per doubling of sound duration for the behavioural threshold. The significance of the results for sexual acoustic communication as well as for bat defence is discussed.     

FIELD RECORDINGS OF ECHOLOCATION AND SOCIAL SIGNALS FROM THE GLEANING BAT MYOTIS SEPTENTRIONALIS

ABSTRACT

We recorded echolocation and ultrasonic social signals of the bat Myotis septentrionalis. The bats foraged for insects resting on or fluttering about an outdoor screen to which they were attracted by a ‘backlight’. The bats used nearly linearly modulated echolocation signals of high frequency (117 to 49 kHz, see Tables) with a weak second harmonic. The orientational signals from patrolling bats were about 2.4 ms in duration and occurred at a repetition rate of about 18 Hz (see Figure 3). The signals used by bats as they approached the screen were of shorter duration (0.72 ms) and occurred at higher rates (33.8 Hz) (Table 2 and Figure 4). We registered one feeding ‘buzz’ (Figure 5). We recorded social signals when two bats patrolled the hunting area. The social signals were characterized by their longer durations (6 ms, see Table 1), lower frequencies (70 to 30 kHz), and curvilinear sweeps (Figures 7 and 8). We calculated the source levels of orientational and social signals using the differences in arrival times at three microphones in a linear array (Figures 1 and 2). The source levels were on average 102 dB peSPL at 10 cm (Table 1). We could not calculate source levels of the signals used by bats as they approached the screen at close range, but these signals were much weaker (about 65 dB peSPL at the microphone).     

Ontogenesis of tonotopy in inferior colliculus of a hipposiderid bat reveals postnatal shift in frequency-place code

Summary The postnatal development of midbrain tonotopy was investigated in the inferior colliculus (IC) of the south Indian CF-FM batHipposideros speoris. The developmental progress of the three-dimensional frequency representation was determined by systematic stereotaxic recordings of multiunit clusters from the 1st up to the 7th postnatal week. Additional developmental measures included the tuning characteristics of single units (Figs. 3f; 4f; 5f), the analysis of the vocalised pulse repertoire (Figs. 3e, 4e, 5e), and morphometric reconstructions of the brains of all experimental animals (Fig. 1).The maturation of auditory processing could be divided into two distinct, possibly overlapping developmental periods: First, up to the 5th week, the orderly tonotopy in the IC developed, beginning with the low frequency representation and progressively adding the high frequency representation. With regard to the topology of isofrequency sheets within the IC, maturation progresses from dorsolateral to ventromedial (Figs. 3c, 4c). At the end of this phase the entire IC becomes specialised for narrowly tuned and sensitive frequency processing. This includes the establishment of the auditory fovea, i.e. the extensive spatial representation of a narrow band of behaviorally relevant frequencies in the ventromedial part of the IC. In the 5th postnatal week the auditory fovea is concerned with frequencies from 100–118 kHz (Fig. 4c, d). During subsequent development, the frequency tuning of the auditory fovea increases by 20–25 kHz and finally attains the adult range of ca. 125–140 kHz. During this process, neither the bandwidth of the auditory fovea (15–20 kHz) nor the absolute sensitivity of its units (ca. 50 dB SPL) were changed. Further maturation occurred at the single unit level : the sharpness of frequency tuning increased from the 5th to the 7th postnatal weeks (Q-₁₀-dB-values up to 30–60), and upper thresholds emerged (Figs. 4f, 5f).Although in the adult the frequency of the auditory fovea matches that of the vocalised pulses, none of the juvenile bats tested from the 5th to the 7th weeks showed such a frequency match between vocalisation and audition (Figs. 4e, 5e).The results show that postnatal maturation of audition in hipposiderid bats cannot be described by a model based on a single developmental parameter.Abbreviations BF best frequency - CF constant frequency - Cer cerebellum - CN cochlear nucleus - CO auditory cortex - CUF cuneiform nucleus - DAB days after birth - FAL forearm length - FM frequency modulation - IC inferior colliculus - NLL nucleus of the lateral lemniscus - PAG periaqueductal gray - SC superior colliculus     

Resonance phenomena in the cochlea of the mustache bat and their contribution to neuronal response characteristics in the cochlear nucleus

Summary The cochlea of the mustache bat, Pteronotus parnellii, is very sensitive and sharply tuned to the frequency range of the dominant second harmonic of the echolocation call around 61 kHz. About 900 Hz above this frequency the cochlear microphonic potential (CM) reaches its maximum amplitude and lowest threshold. At exactly the same frequency, pronounced evoked otoacoustic emissions (OAE) can be measured in the outer ear canal, indicating mechanical resonance. The CM amplitude maximum and the OAE are most severely masked by simultaneous exposure to tones within the range from about 61–62 kHz up to about 70 kHz. The data suggest that the mechanism of mechanical resonance involves cochlear loci basal to the 61 kHz position.The resonance contributes to auditory sensitivity and sharp tuning: At the frequency of the OAE, single unit responses in the cochlear nucleus have the lowest thresholds. Maximum tuning sharpness occurs at frequencies about 300 Hz below the OAE-frequency, where the threshold is about 10 dB less sensitive than at the OAE-frequency. In addition, in the frequency range around the OAE-frequency several specialized neuronal response features can be related to mechanical resonance: Long lasting excitation after the end of the stimulus, asymmetrical tuning curves with a shallow high frequency slope and phasic on-off neuronal response patterns. In particular the latter phenomenon indicates the occurrence of local mechanical cancellations in the cochlea.Abbreviations CF constant frequency component of echolocation calls - CM cochlear microphonic potential - FM frequency modulated component of echolocation calls - N1 compound action potential of the auditory nerve - OAE octoacoustic emission - SEOAE synchronous evoked OAE     

Retransmission of echo-like signals: methods and results of studies on nocturnal moths (Insecta)

Studies of capability to echolocate in nocturnal moths using the method of echo-signal retransmission are described in detail. During retransmission the insect was presented not with the echo from some real object but with electronically generated echo-like signal which appears following the certain delay after insect's own acoustic signal. In that way the artificial echo from non-existent obstacle is produced. In the current study the delay was set to 0.5 ms that corresponds to a distance of about 8 cm from obstacle. At the same time there was no any single movement of any object near the flying insect therefore the activities of sensory systems other than auditory did not cause systematical influence on results obtained. Noctuid moths (Noctuidae, Lepidoptera) are acoustically active insects. They are capable of producing ultrasonic clicks during flight. The most typical response of a moth to the retransmission of echo-like stimuli is an activation of own clicks emission that is often accompanied with rise in click amplitude. Using the activation of emission as a criterion of moth's response to the echo-like stimulation we measured echolocational thresholds in three species: Amphipyra pyramidea (36 dB SPL), Enargia paleacea (31 dB SPL) and Blepharita satura (26 dB SPL). The ability to echolocate was also demonstrated in 20 species of subfamilies Catocalinae, Amphipyrinae, Cuculliinae, Hadeninae, Noctuinae, Heliothinae.