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Many studies indicate that various vertebrates and invertebrates use sensory cues to recognize predators and to evaluate predation risk. Lizards and birds frequently occupy the same habitats; consequently, avian predation on lizards has been implicated as an important selective pressure on lizard behavior. However, there are few studies on how lizards respond to nonvisual cues. The response of adult male Brown Anoles (Anolis sagrei) to calls of birds was studied to determine whether they use auditory cues as an indicator of predation risk from birds. Anoles responded significantly more often with head tilt (increased vigilance) during playback of predatory vocalizations (Kestrel and Red-tailed Hawk calls) compared with low-risk stimuli (nonpredatory bird calls and white noise). Responses to auditory cues suggest that male Brown Anoles are able to distinguish the calls of birds known to prey upon lizards from the calls of nonpredatory birds. More important, this study demonstrates that anoles, mos...

In most katydids, females listen to and locate a stationary, singing male for mating. Pair formation differs in phaneropterine katydids where pairs form duets and the male typically Þnds the female after hearing her acoustic reply to his song. We recorded the duetting behavior of two cryptic species of phaneropterines, Amblycorypha rotundifolia (Scudder) and Amblycorypha alexanderi Walker (Tettigoniidae: Phaneropterinae), from populations in their zone of sympatry. The songs of the two species differed in their temporal properties, and the duets differed in the timing of the femaleOs replies with respect to the maleOs song. We also measured the hearing sensitivity and auditory tuning in these species by recording extracellular neural responses to sound stimuli varying in frequency and intensity. Individuals of both species were most sensitive to frequencies near 13 kHz, which corresponds to the frequencies of the malesO calling songs and to the peak frequency in the femalesO tick responses. Both species also responded to pulses with ultrasonic carrier frequencies. For higher amplitude stimuli, neural responses had shorter latencies and more action potentials. Latency functions differed for low-frequency and high-frequency stimuli. These data form the basis for understanding how auditory processing and sexual selection might be involved in the recent diver- gence of these two cryptic species.

Since 1934, the rotundifolia complex of Amblycorypha has consisted of two named species: Amblycorypha parvipennis Stal, occurring from the Mississippi River westward into the eastern edges of the Great Plains, and Amblycorypha rotundifolia, occurring in most of the eastern United States. The latter entity is here shown to consist of at least three species with distinctive calling songs and different but overlapping geographical distributions. At 25C, A. rotundifolia (Scudder) produces 26 calling song units (phonatomes) per s, whereas Amblycorypha bartrami n. sp. Walker, A. parvipennis, and Amblycorypha alexanderi n. sp. Walker produce 10, 5, and 2.8 ph/s respectively. Amblycorypha rotundifolia occurs from Illinois to New York and southward along the Appalachians to northern Georgia. Amblycorypha bartrami occurs in the southeastern states, and A. alexanderi broadly overlaps the distributions of the other two eastern species. Where A. alexanderi and A. rotundifolia are sympatric, the two occur in similar habitats; where A. alexanderi and A. bartrami are sympatric, A. bartrami occurs in more xeric habitats. No morphological characters were found that reliably identify the three eastern species, yet no fewer than three species must be recognized to provide names for populations that behave as distinct species where they co-occur.

We have studied auditory responses in two species of mole cricket (Scapteriscus borellii and S. abbreviatus) to determine (1) whether they show sensitivity to ultrasound, (2) whether their hearing (at both low and high frequencies) is based on the same neural circuitry as that of true crickets, and (3) whether ultrasound sensitivity in different mole cricket species varies with their ability to fly. S. borellii are sensitive to ultrasonic frequencies. There is evidence of a segregation of frequency bands in prothoracic auditory neurons. There are two pairs of omega neurons (ONs) with similar morphology to ON1 of true crickets. The two pairs of ONs differ in tuning. One pair has two sensitivity peaks: at the frequency of the calling song of this species (3 kHz), and in the ultrasonic range (25 kHz). The other pair lacks the high-frequency sensitivity and responds exclusively to frequencies in the range of the species song. These two types are not morphologically distinguishable. In S. abbreviatus, only one class of ON was found. S. abbreviatus ONs are narrowly tuned to the frequency of the species’ calls. A T-neuron had the best ultrasonic frequency sensitivity in S. borellii. This cell showed a broad tuning to ultrasonic frequencies and was inhibited by low-frequency stimuli. A morphologically similar neuron was also recorded in S. abbreviatus, but lacked the high-frequency sensitivity peak of that in S. borellii. We also assessed the responses of flying S. borellii to ultrasound using field playbacks to free-flying animals. The attractiveness of broadcast calling song was diminished by the addition of an ultrasound signal, indicating that S. borellii avoid high-frequency sound. The results indicate that mole crickets process low-frequency auditory stimuli using mechanisms similar to those of true crickets. They show a negative behavioural response to high-frequency stimuli, as do true crickets, but the organization of ultrasound-sensitive auditory circuitry in mole crickets differs from that of true crickets.

Previous studies have shown that sexually signaling males across different taxa show stereotyped spacing behavior that may be related to aspects of their signals, such as intensity. However, few studies have shown that the separation between signaling males affects their relative attractiveness. Using two sound traps broadcasting the calling song of the cricketEunemobius carolinus, we show that the separation, relative intensity, and absolute intensity of the calling songs influence calling song attractiveness. For calling songs separated by 5 m, the proportion of individuals attracted to the higher intensity song increased as the relative intensity difference of the two songs increased from 3 to 6 dB. For calling songs that differed by 6 dB, relative attraction to the less intense song decreased with decreasing song separation. These two results are consistent with the predictions of a model (Forrest and Raspet, 1994) that suggests that dense spacing is more costly for less powerful singers and that this cost increases with increasing differences in relative intensity. When the relative intensity of the songs was held constant (6 dB), we found that discrimination between songs decreases as the song absolute intensity increases. In particular, a greater proportion of individuals was attracted to the high-intensity song when the songs were broadcast at 103 and 97 dB than when the songs were broadcast at 109 and 103 dB. Unlike mammals and birds, the ability ofE. carolinus to discriminate between songs that differ in intensity may decrease as the absolute intensity increases. This may mean that females are less discriminating when they are closer to singing males.

Green [Time Resolution in Auditory Systems, 1985] distinguished between two broad classes of paradigms that presumably represent the two ends of the auditory temporal processing continuum. At one extreme are measures of temporal integration (TI) that estimate the maximum time over which acoustic information can be stored. At the other extreme are measures of temporal acuity/resolution (TA) that estimate the briefest detectable change in acoustic information. The goal of both paradigms is to estimate a time constant (τ) for the auditory system. Traditionally, τ1 reported for TI is more than an order of magnitude longer than τA estimated for TA. The aim of this study was to resolve this apparent paradox. Detection thresholds were obtained for a range of brief bandlimited (WN=62–6000 Hz) increments within a broadband noise to estimate τ in TI and TA tasks from the same listeners. For each WN condition, detection thresholds were measured as a function of (1) increment duration (PN=10–480 ms) by tracking incre...

We sampled a population of signalingPhoturis versicolor quadrifulgens fireflies to quantify the variation in flash patterns emitted by males. Males produced five distinct flash patterns during their mate-searching flights. Four of the patterns consisted of two to five equal-intensity pulses and the fifth pattern type was a flicker, a group of rapid modulations in intensity. We found that the proportions of each pattern remained relatively constant from night to night throughout the season. The different flash patterns produced varied significantly with time of night; patterns having fewer pulses occurred earlier in the evening. Local density, an estimate of competition, did not significantly correlate with flash pattern type. On consecutive emissions, individuals changed their flash types with a mean probability of 0.12 (over all males), and they usually switched between patterns differing by a single pulse (from a two- to a three-pulse pattern, from a three- to a two-pulse pattern, etc.). The nightly temporal changes in flash patterns may be related to tradeoffs between female availability and energetic costs of signaling or the changes may be related to increased predation risk from visual predators.

SYNOPSIS. Acoustic signals transmitted over large distances differ significantly from those emitted by the signaler. Acoustic signals degrade in amplitude, spectral and temporal structure as they propagate through theenvironment. A great deal of work on acoustic communication is aimed at understanding the selective forces imposed by the environment on animal signals. I will discuss the physical constraints the environment puts on acoustic communication, and then discuss similarities in communication by anurans and insects that relate these environmental constraints to their signaling systems. Lastly, I show how changes in signals during propagation relate to changes in signal perception during phonotaxis, and thus, how propagation relates to mate choice and sexual selection

Measurements of sound propagation were made in a shallow, sloping bottomed freshwater pond. The frequency responses of the pond had a highpass characteristic with a sharp cutoff frequency. Cut-off frequency of the response was inversely related to the depth of water at the shallowest transducer (either projector or receiver) and was the same whether propagating downslope or upslope (reciprocity). The relationship between cut-off frequency and depth was significantly different from that expected for propagation in a channel with either a rigid or pressure release (gas) bottom. The highpass characteristic is due to modal propagation in the ‘waveguide’, and the effect of this environmental filtering is 30–60 dB between frequencies that propagate and those that do not. Thus, the physical constraints of this shallow-water environment on acoustic communication by aquatic animals are much greater than those measured in terrestrial environments. These constraints are discussed relative to selection for b...

The purpose of this study was to compare the role of frequency selectivity in measures of auditory and vibrotactile temporal resolution. In the first experiment, temporal modulation transfer functions for a sinusoidally amplitude modulated (SAM) 250-Hz carrier revealed auditory modulation thresholds significantly lower than corresponding vibrotactile modulation thresholds at SAM frequencies greater than or equal to 100 Hz. In the second experiment, auditory and vibrotactile gap detection thresholds were measured by presenting silent gaps bounded by markers of the same or different frequency. The marker frequency F1 = 250 Hz preceded the silent gap and marker frequencies after the silent gap included F2 = 250, 255, 263, 310, and 325 Hz. Auditory gap detection thresholds were lower than corresponding vibrotactile thresholds for F2 markers less than or equal to 263 Hz, but were greater than the corresponding vibrotactile gap detection thresholds for F2 markers greater than or equal to 310 Hz. When the auditory gap detection thresholds were transformed into filter attenuation values, the results were modeled well by a constant-percentage (10%) bandwidth filter centered on F1. The vibrotactile gap detection thresholds, however, were independent of marker frequency separation. In a third experiment, auditory and vibrotactile rate difference limens (RDLs) were measured for a 250-Hz carrier at SAM rates less than or equal to 100 Hz. Auditory RDLs were lower than corresponding vibrotactile RDLs for standard rates greater than 10 Hz. Combination tones may have confounded auditory performance for standard rates of 80 and 100 Hz. The results from these experiments revealed that frequency selectivity influences auditory measures of temporal resolution, but there was no evidence of frequency selectivity affecting vibrotactile temporal resolution.

Attraction of flying mole crickets to individual males calling in an outdoor arena was influenced significantly by the relative intensity of the males calling in the arena. Louder males attracted more individuals than males whose calling songs were less intense. Making simple assumptions about the acoustic output from calling males and about the flight pattern and response of flying females, the differential attraction can be explained by a mathematical model. Computer simulation of the model was used to examine the importance of a male's intensity relative to others and the effect of distance between males on the attraction of females. The model and its relation to active female choice and passive attraction are discussed. The model makes predictions about differences in spacing behaviour of males that maximize attraction relative to other males.

We have studied auditory responses in two species of mole cricket (Scapteriscus borellii and S. abbreviatus) to determine (1) whether they show sensitivity to ultrasound, (2) whether their hearing (at both low and high frequencies) is based on the same neural circuitry as that of true crickets, and (3) whether ultrasound sensitivity in different mole cricket species varies with their ability to fly. S. borellii are sensitive to ultrasonic frequencies. There is evidence of a segregation of frequency bands in prothoracic auditory neurons. There are two pairs of omega neurons (ONs) with similar morphology to ON1 of true crickets. The two pairs of ONs differ in tuning. One pair has two sensitivity peaks: at the frequency of the calling song of this species (3 kHz), and in the ultrasonic range (25 kHz). The other pair lacks the high-frequency sensitivity and responds exclusively to frequencies in the range of the species song. These two types are not morphologically distinguishable. In S. abbreviatus, only one class of ON was found. S. abbreviatus ONs are narrowly tuned to the frequency of the species' calls. A T-neuron had the best ultrasonic frequency sensitivity in S. borellii. This cell showed a broad tuning to ultrasonic frequencies and was inhibited by low-frequency stimuli. A morphologically similar neuron was also recorded in S. abbreviatus, but lacked the high-frequency sensitivity peak of that in S. borellii. We also assessed the responses of flying S. borellii to ultrasound using field playbacks to free-flying animals. The attractiveness of broadcast calling song was diminished by the addition of an ultrasound signal, indicating that S. borellii avoid high-frequency sound. The results indicate that mole crickets process low-frequency auditory stimuli using mechanisms similar to those of true crickets. They show a negative behavioural response to high-frequency stimuli, as do true crickets, but the organization of ultrasound-sensitive auditory circuitry in mole crickets differs from that of true crickets.

We describe the paired hearing organ of the scarab beetle Euetheola humilis. The auditory structures of the beetle are typical of other insect ears in that they have a thinned tympanic membrane backed by a tracheal airsac with associated chordotonal sensory structures. The tympanic membranes of the beetle are part of its cervical membrane and are located behind the head, where the cervix attaches dorsally and laterally to the pronotum. Each membrane is approximately 3 μm thick. The chordotonal sensory organ, which lies within the tracheal airsac, contains 3–8 scolopidia that attach by accessory cells directly to the tympanic membrane. Neurophysiological recordings from the neck connective of the beetle revealed that the auditory system is sensitive to frequencies between 20 and 80 kHz and has a minimum threshold of approximately 58 dB at 45 kHz. The neurophysiological audiogram is identical to the behavioral audiogram for a head roll, one behavioral component of the beetle’s startle response elicited by ultrasound. Blocking experiments show that the membranous structures on the cervix are indeed the hearing organs. Neurophysiologically determined thresholds increased by more than 35 dB when drops of water covered the tympanic membranes and were essentially restored to the control level when the water was later removed. At least three other genera of Dynastinae scarabs have similar tympanum-like structures located in their cervical membranes. Behavioral and neurophysiological data show that the frequency tuning of species in two of these genera, Cyclocephala and Dyscinetus, is nearly identical to that of E. humilis. Our discovery represents only the second group of beetles known to respond to airborne sounds. However, the hearing organs of these scarab beetles differ in structure and placement from those of the tiger beetles, and thus they represent an independent evolution of auditory organs in the Coleoptera.

Gap detection thresholds were measured by forced-choice procedure for conditions where the duration of a silent gap was varied adaptively between pairs of sinusoidal markers of the same or different frequency. Frequencies of the first sinusoid in a pair of markers ranged from F1 = 500 to 4000 Hz. Second-sinusoid marker frequencies F2 included F1 = F2, and usually frequencies 2%, 5%, 24%, and 50% higher than F1. In preliminary studies the role of presentation level (E/N0) on gap detection was considered. Preliminary data revealed confounding extraneous factors arising from gating transients and from overall stimulus (i.e., markers + gap) and/or masker duration cues. In the main experiments, the contributions of these extraneous cues were evaluated with experimental designs aimed at identifying and minimizing the confounding roles of these cues in gap detection. For conditions where extraneous gating transient cues were minimized (by presenting the sinusoidal markers in a continuous noise masker with random onset phase for the second sinusoid in every pair of markers) and overall stimulus duration cues were diminished (by randomizing the duration of each marker independently), gap detection thresholds increased from 5 to 90 ms as the frequency separation between F1 and F2 was increased by half an octave. When the gap detection thresholds were treated as filter attenuation values by normalizing and converting the data into decibels, the data were closely fit by the roex filter model. On average, the listeners' performances were modeled well by a constant-percentage (7%) bandwidth filter centered on F1.

The temporal envelope detector [N. Viemeister, J. Acoust. Soc. Am. 66, 1364–1380 (1979)] is a good single‐channel model for auditory temporal processing. The model has three stages: (1) an initial bandpass filter, followed serially by (2) a nonlinear element, and (3) a lowpass filter. A digital version of the model using a max–min decision rule [Forrest and Green, J. Acoust. Soc. Am. 82, 1933–1943 (1987)] at the model’s output has been used to simulate temporal gap detection (TGD) thresholds for silent temporal gaps in pairs of sinusoidal markers (F1 and F2). Simulated TGD thresholds were measured as a function of marker frequency separation in the same manner as described in psychophysical experiments [Formby et al., companion paper at this meeting]. Simulated TGD thresholds depended directly on marker frequency separation. For a given frequency separation, simulated TGD thresholds were minimized by centering the symmetrical, first‐stage roex filter between the two marker frequencies. This single‐channel...

Scotch broom, Cytisus scoparius (L.), a weed in the Pacific Northwest, is rapidly invading open areas and ecologically sensitive dunes along the coast. Scotch broom populations also exist in the eastern United States, but are apparently stable and not expanding. The eastern Scotch broom populations may be kept in check by the broom weevil, Bruchidius villosus (F.), a bruchid found in eastern populations of broom but absent from those in the Northwest (Bottimer 1968). We studied the natural history and biology of the broom weevil in North Carolina. Our purpose was to relate the bruchidis life history to the phenology of the host plant and to quantify oviposition and seed destruction by the bruchids. Adult weevils were active around the plant from the first flowering in early spring until dehiscence of the seedpods in summer. The sex ratio of the beetles was nearly 1:1 throughout the adult activity season. The number of weevil eggs laid on the pods was correlated to the length of the pod and to the number of seeds in the pod. The larvae develop in and destroy the seeds of the broom plant. Seed destruction at two sites in North Carolina was more than 80%; a field experiment showed that seed destruction was dependent on the density of beetles in cages on the plants. Because of its impact on seed production, the broom weevil may be a viable candidate for biological control of broom in the Northwest.

The signals generated by acoustic insects exhibit temporal patterns on several time scales. Annual or seasonal rhythms provide information about temporal changes in insect population size. Knowledge of such changes might be useful in ecological monitoring programs. Circadian or daily rhythms commonly seen in insect signaling are generated by endogenous ‘‘clocks’’ that are reset by environmental cues. Understanding these daily patterns is also important for monitoring insect populations. Within insect populations, the signals of neighbors sometimes show temporal patterns of synchrony or alternation with timing on the order of seconds. The phase relationships among individuals are maintained by acoustic resetting, whereby an individual’s temporal rhythm will change depending on the phase that neighboring signals are received. On still smaller time scales, temporal patterns of insect songs are diverse and generally differ among species. These small‐scale patterns are often essential components of mating signals and are used in mate recognition and mate choice.

Snowy tree crickets produce a rhythmic acoustic signal composed of short chirps. The chirp rhythms are very regular and dependent on temperature. When signaling in groups, males synchronize their chirps. The rhythmic signals of these tree crickets were used as a model of a ‘‘biological oscillator.’’ The phase responses of males to single probe stimuli similar to the male calling song were measured. The phase response curves (PRC) of males showed both strong (type 0) and weak (type 1) resetting. PRCs differed depending on amplitude, duration, and frequency of the resetting stimuli. In other experiments, males could adjust their natural periods by as much as 15% when phase‐locking (1:1) to an entrainment stimulus. Signaling behavior of males was compared with a simple model of coupled oscillators. The phase resetting was not consistent with the simplest resetting model, in which the male’s phase shift is completed after one cycle of the chirp period. In addition, a simple iteration of the PRC could not simulate the phase‐locking observed in the entrainment experiments indicating that the acoustic coupling between males differs from a simple resetting model.

Temporal gap detection (TGD) thresholds measured for silent gaps as a function of the frequency separation between a fixed‐frequency pre‐gap sinusoidal marker (F1) and a variable‐frequency post‐gap sinusoidal marker (F2) may be confounded by off‐frequency listening (Formby et al., Aud. Neurosci. 3, 1–20). Evidence of this confounding role comes from simulation experiments with a single‐channel envelope detector model. TGD stimulation results suggest that listeners can improve the signal‐to‐noise ratio and, in turn, TGD performance by adjusting their optimal auditory filter so that it is centered between F1 and F2 (Forrest and Formby, Aud. Neurosci. 3, 21–33). Off‐frequency listening between F1 and F2 may result in underestimates of TGD thresholds that appear as asymmetries in detection performance for F2 markers presented below and above the F1 frequency. To obtain more precise estimates of TGD, unaffected by off‐frequency listening, performance has been measured and will be reported for three listeners w...

The tonal quality and temporal complexity of bird vocalizations have long suggested that birds may excel in auditory spectral or temporal processing. However, most psychophysical studies support the notion that birds have spectral and temporal resolving power roughly comparable to that measured in humans. Rarely have such psychophysical tasks involved both frequency and time cues. An intriguing aspect of gap‐detection experiments with sinusoidal markers is the robust dependence on the frequency separation between the markers. In humans, silent gaps become more difficult to discriminate as the frequency difference between the markers increases. This frequency‐dependent pattern of thresholds is well fit with a roex‐filter model. Here, budgerigars were trained by operant conditioning to discriminate a change in the duration of a silent gap between two tonal markers. Frequency separation between the tonal markers had only a small effect on gap discrimination thresholds in budgerigars, suggesting an unusually ...

Formby and Forrest [J. Acoust. Soc. Am. 89, 830–837 (1991)] measured temporal gap detection (TGD) thresholds as function of frequency separation between two sinusoids marking a silent temporal gap. Their results were fit well with a roex‐filter model. Filter estimates (1) were based on TGD thresholds for post‐gap marker frequencies F2≥ pre‐gap marker frequencies F1 and (2) assumed symmetry of the roex‐filter function for F2≤F1. In a related study, TGD thresholds were measured with narrow‐band markers [Formby et al., J. Acoust. Soc. Am. 93, 1023–1027 (1993)]. The resulting thresholds raised doubts about the earlier assumption of filter symmetry. To resolve this issue, TGD thresholds were measured for F2 frequencies presented above and below F1=500 and 4000 Hz for a range of marker and masker presentation levels. Roex functions fitted for conditions of F2≥F1 were typically shallower than those fitted for conditions of F2≤F1. The same qualitative patterns of filter asymmetry have also been found and will be ...

Computer simulations were implemented for estimating detection thresholds for silent temporal gaps in sinusoidal markers that differed in frequency. The stimuli were presented in blocks of 50. 2AFC trials in the same adaptive paradigm used to measure human temporal gap detection (TGD) thresholds [Formby et al., companion paper at this meeting]. The stimuli were preprocessed by a multi‐channel, multi‐resolution cochlear model. The digital simulation of the cochlear model was implemented by a 30‐channel basilar membrane filter bank, followed by 30 hair cell/synapse sections [Liu, Ph.D. dissertation, Johns Hopkins Univ. (1992)]. The output for each channel of the cochlear model was lowpass filtered, and a max–min ratio [Forrest and Green, J. Acoust. Soc. Am. 82, 1933–1943 (1987)] was estimated for each of the 30 channels. A majority vote across the 30 max–min ratio values on each trial was used to select the observation interval containing the silent gap. Results from this majority voting scheme were qualitatively similar to, but consistently poorer than, human psychoacoustic TGD thresholds [Formby et al., companion paper at this meeting]. Other decision rules are being investigated and will be presented for simulating human thresholds. [Research supported by NIH.]

Insects have a vast array of mechanisms for producing acoustic signals and receiving sound stimuli. Because of their small size, insects have special physical problems in producing efficient signals and localizing sound sources (signaling insects). Communicative sounds may be airborne, substrate borne vibration, or surface waves and are produced by movement of air, percussion, or stridulation. Reception may involve detection of particle displacement or pressure. These different modes of sound production and reception are discussed. Important mechanisms that have evolved in response to the insects’ physical problems of sound production and reception are shown.

Frequency responses of shallow, freshwater ponds in northern Mississippi were measured. The response has a highpass characteristic with a sharp cutoff frequency due to the modal properties of the system. The cutoff frequency of the system is inversely related to the depth of water at the shallower transducer (projector or receiver). Frequencies below the first mode are nonpropagating, and the overall effect of this environment on propagation is about 50 dB. Several species of aquatic insects communicate in these shallow‐water ponds using acoustic signals, and they must contend with the physical constraints imposed by the system. Data on the calling song (long range) of a common aquatic beetle (Tropisternus collaris, Hydrophilidae) are presented and discussed in relation to the propagation characteristics of their shallow pond habitats. [Work supported by USDA.]

Indirect tests of residual auditory function often assume that the temporal envelope is the primary cue in the acoustic signal for profoundly hearing‐impaired persons who are without auditory function. In contrast, for hearing‐impaired persons who retain residual auditory function, both temporal envelope and spectral cues are available. This hypothesis was evaluated directly by studying simultaneously temporal envelope and spectral resolution in seven profoundly hearing‐impaired subjects (ten ears). Amplitude modulation (AM) detection thresholds were measured with a 250‐Hz carrier, modulated at rates of 40 and 150 Hz, presented by headphones and by hand vibration. At 40 Hz, where the AM sidebands fell within the same critical band as the carrier and could not be resolved, all subjects yielded similar headphone and vibrator results. At 150 Hz, headphone thresholds for six ears were better than the vibrotactile threshold, while four ears yielded little or no difference in performance between the two transducers. The latter results reflect differences in resolution between ears with and without functional critical band mechanisms and, hence, inherent differences between auditory and vibrotactile processing. [Research supported by NIH.]

To infer mating preferences of female Neonemobius sp., we monitored their proximity to males paired in laboratory enclosures. Females were found significantly more often near the larger of the males, and more often near a calling male than a silent one. The proportion of time individual males were observed calling was significantly correlated with male size. Females did not prefer virgin to mated males. When allowed to mate, females mated with the larger of the pair 5 of 7 times. Female preference for large males may result from selection on females to obtain larger investments from males. Female nemobiine crickets feed on glandular secretions provided by males during mating. Large males may offer more material, and females may use male calling songs as a cue to male size.

Gap detection thresholds were measured by forced‐choice procedure for conditions where the duration of a silent gap was varied adaptively between pairs of sinusoids of the same or different frequency. Frequencies of the first sinusoid in a pair were F1 = 500, 1000, 2000, and 4000 Hz. Second‐sinusoid frequencies, F2, included F1 = F2, and frequencies 2%, 5%, 24%, and 50% higher than F1. To minimize the influence of extraneous cues, the onset phase of the second sinusoid in each pair of tones and overall duration of each sinusoid in a pair of tones were randomized. Sinusoids were presented in continuous broadband noise (N0 = 30 dB/Hz) at an average E/N0 = 40 dB. Gap detection thresholds increased from 5 to 90 ms as the frequency separation between F1 and F2 was increased. The gap detection thresholds were treated as filter attenuation values by normalizing and converting the data into decibels, and then fitting the roex filter model. On average, the listeners' performances were modeled well by a constant‐pe...

Results of experiments on the detection of silent intervals, or gaps, in broadband noise are reported for normal-hearing listeners. In some preliminary experiments, a gap threshold of about 2 ms was measured. This value was independent of the duration of the noise burst, variation of the noise level on each presentation, or the temporal position of the gap within the noise burst. In the main experiments, the thresholds for partial decrements in the noise waveform as well as brief increments were determined. As predicted by a model that assumes a single fixed peak-to-valley detection ratio, thresholds for increments are slightly higher than thresholds for decrements when the signal is measured as the change in rms noise level. A first-order model describes the temporal properties of the auditory system as a low-pass filter with a 7- to 8-ms time constant. Temporal modulation transfer functions were determined for the same subjects, and the estimated temporal parameters agreed well with those estimated from the gap detection data. More detailed modeling was carried out by simulating Viemeister's three-stage temporal model. Simulations, using an initial stage bandwidth of 4000 Hz and a 3-ms time constant for the low-pass filter, generate data that are very similar to those obtained from human subjects in both modulation and gap detection.

Lifetime oviposition by caged, individual female southern and tawny mole crickets, Scapteriscus acletus Rehn & Hebard and S. vicinus Scudder, was monitored outdoors; oviposition was highly seasonal. Females that matured in the fall did not oviposit until the following spring along with females that matured in the spring. Most eggs were laid in May and June and percent hatch of clutches decreased later in the season. Dry weight of eggs, number of eggs per clutch, and percent hatch decreased with successive clutches from individual females. Average investment in eggs per clutch ranged from 10 to 24% of female body weight for S. acletus and from 5 to 16% for S. vicinus females. Lifetime investment was >100% of female body weight for 6 of 12 S. acletus females, but only 1 of 8 S. vicinus females had a lifetime investment in eggs equaling its body weight. In S. acletus, but not S. vicinus, large females produced more offspring and average size of their egg clutches was larger than those of smaller females.

Insect size tactics or developmental strategies are discussed in relation to decisions individuals make about when to mature. Such decisions carry with them costs and benefits in terms of that individual's reproductive success. Whenever size affects fitness, selection should act such that individuals evaluate the costs and benefits due to changes in size and should mature when the ratio of benefit to cost is maximized.Predictions about seasonal changes in adult sizes within a population are tested on two species of mole cricket, Scapteriscus acletus and vicinus. Specifically, individuals maturing in the fall should be larger than average because there is no cost associated with delayed reproduction since reproduction occurs only during spring months. Smaller than average individuals should remain in juvenile stages and get larger before reproducing. Also it is predicted that as the spring reproductive season progresses a greater proportion of smaller individuals should mature because the costs due to delaying reproduction increase. The changes in seasonal distribution of adult sizes of mole crickets support the predictions and suggest that individuals make decisions about when to mature based on costs and benefits associated with changes in size.

Seven experiments on the detectability of intensity changes in complex multitonal acoustic spectra are reported. Two general questions organize the experimental efforts. The first question is how the detectability of a change in a flat (equal energy) spectrum depends on the frequency region where a single intensive change is made. The answer is that frequency region plays a relatively minor role. Frequency changes in the midregion of the spectrum are the easiest to hear, but thresholds increase by only about 5 dB over the range from 200 to 5000 Hz. For all frequencies, the psychometric function is of the form d' = k(delta p), where k is a constant and delta p is the change in pressure. The second question is how can we predict the detectability of complex changes over the entire frequency range from the detectability of change at each separate region. Thresholds for detecting a change from a flat spectrum to a spectrum whose amplitude varies in sinusoidal ("rippled") fashion over logarithmic frequency are measured at different frequencies of ripple. The thresholds are found to be independent of ripple frequency and are 7 dB higher than predicted on the basis of an optimum combination rule.

The ability of human observers to detect partially filled or completely silent intervals (gaps) was measured using a variety of different waveforms. The slopes of the psychometric functions for gap detection using broadband noise are dependent upon the amount of noise remaining during the gap. For completely silent intervals, the psychometric function covers a range of only 2 ms, but the psychometric functions for partially filled intervals are less steep. The detection of gaps in narrow‐band noise (surrounded by complementary band‐reject maskers) is strongly influenced by the signal‐to‐noise ratio. The signal bandwidth and center frequency also influence detectability. Gap detection improved as signal bandwidth increased, and detection improved when signal bands containing gaps were centered at higher frequencies. Detection of gaps in single components of a 21‐component, equal‐amplitude complex also showed lower thresholds as the frequency of the component containing the gap increased. Increasing the number of components in the complex that contained the gap improved the detectability of the gap, more so when the gaps were all presented at the same time (synchronous condition). Uncertainty about the temporal position of the gap within the observation interval made the gap more difficult to detect. This temporal uncertainty effect occurred for gaps in broadband noise, in narrow‐band noise, and in sinusoidal waveforms.

Spectral shape discrimination, or profile analysis, of complex waveforms (21 components) in the presence of broadband noise and special sinusoidal maskers of random amplitude was studied. The first experiment involved the discrimination between a standard flat spectrum and a ‘‘rippled’’ spectrum in broadband noise of different spectrum levels. Thresholds obtained under control conditions, without noise or without a standard, were used to estimate constants of an equation that predict thresholds where standard and noise are both present. The model assumes an external variance, produced by the noise, is added linearly to an internal variance caused by the flat standard. The mean squared error is less than 2 dB. The second experiment involved the detection of an increment on the center component of the 21‐component standard. Added to the standard was an additional masking sinusoid of random amplitude. Both the frequency and the range of the random amplitude were varied and both showed a systematic influence on the detectability of the 1000‐Hz increment.

Decrements in broadband noise stimuli were produced by changing the intensity of the noise for a brief interval. As the duration of the interval increases, less change in level is needed to detect the alteration. One can interpret these experiments as probing the impulse response of the auditory temporal mechanism in the manner suggested by Buunen and van Valkenburg [Jr. Acoust. Soc. Am. 65, 534–537 (1979)]. Unlike their results, our measurements are well fit by an exponential function with a short (8–10 ms) time constant. Our results are consistent with the model proposed by Viemeister [Jr. Acoust. Soc. Am. 66, 1364–1380 (1979)] to explain his results obtained with the modulation transfer function (MTF). Direct measurement of the modulation transfer function for these same listeners indicates good agreement between the time constant measured in the gap experiment and the low‐pass break point measured in the MTF. We also explored increments in the noise stimuli instead of decrements. The data show symmetry when the increase or decrease in the noise rms is used to express the change in the stimulus. [Work supported by a grant from the National Science Foundation.]

Mole crickets are common pests of turfgrass and pastures in the southeastern United States. The males produce species‐specific calling songs that function to attract mates. Males begin calling after sunset from a burrow constructed prior to calling. The burrow's opening expands exponentially and the burrows are “tuned” during their construction. Output increases 20 dB during the tuning process. Sound fields are hemispherical. Power output ranges from 4 to 20 μW and is dependent upon the size of the male and the moisture of the soil surrounding the burrow. Flying females respond to the calling song and land near calling males. Males calling in an outdoor arena were highly variable in the number of individuals attracted to their calling songs. Intensity differences among the males was the major determinant in the response of females to males in the arena. The differential response to calling males can be explained using a simple model of pressure fields surrounding two sources.

The southern mole cricket, Scapteriscus acletus, is known throughout the Southeast as an important agricultural and turfgrass pest. Several decades of research on these insects have not yielded satisfactory control methods, perhaps because little has been learned of their basic biology and reproductive behavior. This lack of knowledge stems from the fact that mole crickets are burrowing crickets, spending most of their lives underground. Male and female external morphologies are identical except for the forewings. Male S. ac7ctus, as in many cricket species, produce sound to attract sexually responsive females (Alexander 1975). The sound producing apparatus is manifest as a black spot on the male's forewing; it consists of a scraper and a stridulatory file on each forewing. Sound is produced during stridulation when the scraper of one wing rubs the file of the other wing. Although this apparatus is typical of acoustical crickets, mole crickets are unique in their acoustical behavior. Males call from within special burrows they construct each night prior to calling. Using their fossorial forelegs and large pronotum, males pack and shape the opening of their burrow into an exponentially expanded horn. Bennet-Clark (1970) has shown that this shape amplifies male calling songs in 2 European mole crickets, Gryllotalpa gryllotalpa and G. vineae. This amplification probably holds true for S. acletus (Nickerson, Snyder, and Oliver 1979). Male S. acletus produce a continuous trill during the calling period. This song is species-specific with a carrier frequency of about 2.7 kHz modulated at 50 pulses per second (Ulagaraj 1976). I placed individual S. acletus males in soil-filled, 19-liter buckets. These buckets were covered with aluminum screen to prevent the male escaping, placed in a pit, and surrounded by a trapping device (Fig. 1). Males could then be observed for calling behavior and responding animals trapped around the buckets. A modification was made to assess flight from buckets: the aluminum screen cover was removed and the entire trap covered with a cylindrical hardware cloth cage. Individuals flying from buckets hit the cage, fell, and were trapped around the buckets. Twelve S. acletus males were monitored for nightly calling period with respect to sunset (Fig. 2a). Individual males differed significantly in their

Male crickets produce calling songs that function to attract mates. Sound is produced when membranes of the wings are caused to vibrate during stridulation. Sound fields were measured for three species of crickets. Two species of mole crickets, Scapteriscus acletus and s. vicinus, call from within burrows constructed in the soil. Sound fields of the mole crickets were hemispherical and the power output averaged 4 μW (N = 22, range 2–22 μW). Power output was dependent upon male size and moisture content of soil surrounding the burrow. Efficiency of sound production was estimated to be less than 0.2%. Sound fields of a species of tree crickets, Oecanthus quadripunctatus, approximated that of a doublet source. Power output ranged from 2–17 μW (N = 6) and efficiency was estimated at about 1%.

Accurate estimates of population size are needed to understand the population dynamics of any species. They are also needed to determine when to implement a specific control tactic, and to measure whether that control tactic has been effective. This paper discusses the use of acoustic signals produced by insects and the feasibility of using these signals to census populations. Insect sounds are either incidental (produced as a by-product of some activity) or non-incidental (produced to cause a response in some other animal). Incidental sounds differ from non-incidental sounds with respect to several features that are important to using sound to census populations. These features include species specificity, frequency content, ease of localization, distance traveled, and the duration and timing of sound production. Studies of crickets show that information about which individuals in a population are producing sound, when the individuals produce sound (seasonally and daily), and the probability that individuals produce sound during census periods must be known to accurately estimate the size of a population.

Wing folding in the Insecta evolved early in the history of the group and often the wings are folded one on top of the other over the abdomen. Whether or not the right wing is folded over the left or vice versa is of little importance except when the two wings have evolved different tasks. Such is the case in a number of families of Orthoptera: Gryllidae, Gryllotalpidae, Haglidae, and Tettigoniidae. In these families the forewings of the males are specialized for sound production. The plectrum, or scraper, of one wing is drawn across the pars stridens, or file, on the underside of the other wing. This action causes certain membranes of the wing to vibrate and produce sound. Usually the right wing rests over the left in crickets and the left rests over the right in katydids. Interestingly, the females, whose wings are not usually adapted to produce sound, follow the same rules (Masaki et al. 1987). In many species, because of the specialization of the two wings, they differ considerably with respect to pigmentation, reduction in the number of teeth on the file, and in retrogression of the file (Masaki et al. 1987). In the haglids the males may sing using the left over the right or the right over the left (Morris & Gwynne 1978) and apparently can switch while singing (Spooner 1973). I have examined the wingedness of both sexes in two species of mole cricket, Scapteriscus acletus and S. vicinus, to determine how they relate to the other three groups. Individuals were collected as part of another study (Forrest 1986 ) from the routine sound-trapping station on the Agronomy Farm of the University of Florida (Walker et al. 1983). Quarter-monthly samples of up to 50 individuals were collected during the crickets' spring and fall flights of 1981 and 1982. A total of 1431 S. acletus females, 1222 S. acletus males, 714 S. vicinus females, and 284 S. vicinus males were captured and classified as to wing overlap. These are the largest samples of singing Orthoptera where the wingedness of individuals has been studied. In neither sex of either species did rightand left-wingedness differ from 50:50. Female acletus were 51% right-winged (734:697), males were 49% right-winged (602:620). For vicinus, females were 51% right-winged (367:347) and males were 48% right-winged (135:149). I also examined 19 (2 males and 17 females) Neocurtilla hexadactyla, the northern mole cricket, from the Florida State Collection of Arthropods. Both males had right wings over left but only 5 of the 17 females were this way. Checking two other species of mole cricket, Scapteriscus abbreviatus [n= 13; males (4:4), females (1:4)] and Gryllotalpa africana (n=4), revealed at least some specimens with each configuration. Masaki et al. (1987) found equal numbers of left-winged and right-winged males of a scaly cricket, Ornebius kanetataki. I examined 30 male Cycloptilum antillarTium, another mogoplistine, from the collection and found 16 (53%) with their right wing over their left. It is interesting that the mole crickets and scaly crickets would differ so greatly from the other gryllids and tettigoniids with respect to the constancy of wing overlap. One possible reason for the differences might be because of the ancestry of the group. Evidence from the fossil record leaves "no doubt that mole crickets developed from