Female Flight Tones Research Articles

Multimodal integration: Audio-visual integration by swarming mosquitoes

Mosquitoes are notorious for swarming. A new study shows that multi-sensory integration, in particular the way that male mosquitoes' behavioural responses to visual stimuli are modulated by female flight tones, plays a key part in this swarming behaviour.

Mosquitoes integrate visual and acoustic cues to mediate conspecific interactions in swarms

Male mosquitoes form aerial aggregations, known as swarms, to attract females and maximize their chances of finding a mate. Within these swarms, individuals must be able to recognize potential mates and navigate the social environment to successfully intercept a mating partner. Prior research has almost exclusively focused on the role of acoustic cues in mediating the male mosquito's ability to recognize and pursue females. However, the role of other sensory modalities in this behavior has not been explored. Moreover, how males avoid collisions with one another in the swarm while pursuing females remains poorly understood. In this study, we combined free-flight and tethered-flight simulator experiments to demonstrate that swarming Anopheles coluzzii mosquitoes integrate visual and acoustic information to track conspecifics and avoid collisions. Our tethered experiments revealed that acoustic stimuli gated mosquito steering responses to visual objects simulating nearby mosquitoes, especially in males that exhibited a strong response toward visual objects in the presence of female flight tones. Additionally, we observed that visual cues alone could trigger changes in mosquitoes' wingbeat amplitude and frequency. These findings were corroborated by our free-flight experiments, which revealed that Anopheles coluzzii modulate their thrust-based flight responses to nearby conspecifics in a similar manner to tethered animals, potentially allowing for collision avoidance within swarms. Together, these results demonstrate that both males and females integrate multiple sensory inputs to mediate swarming behavior, and for males, the change in flight kinematics in response to multimodal cues might allow them to simultaneously track females while avoiding collisions.

Differences in male Aedes aegypti and Aedes albopictus hearing systems facilitate recognition of conspecific female flight tones

When Aedes albopictus mosquitoes invade regions predominated by Aedes aegypti, either the latter can be displaced or the species can coexist, with potential consequences on disease transmission. Males from both species identify females by listening for her flight sounds. Comparing male hearing systems may provide insight into how hearing could prevent interspecific mating. Here, we show that species-specific differences in female wing beat frequencies are reflected in differences in male ear mechanical tuning frequencies and sound response profiles. Though Aedes albopictus males are attracted to sound, they do not readily display abdominal bending, unlike Aedes aegypti. We observed interspecific differences in male ear mechanical, but not electrical, tuning, suggesting a conserved primary auditory processing pathway. Our work suggests a potential role for hearing in the premating isolation of Aedes aegypti and Aedes albopictus, with implications for predicting future dynamics in their sympatric relationships and our understanding of mosquito acoustic communication.

Hearing of malaria mosquitoes is modulated by a beta-adrenergic-like octopamine receptor which serves as insecticide target

Malaria mosquitoes acoustically detect their mating partners within large swarms that form transiently at dusk. Indeed, male malaria mosquitoes preferably respond to female flight tones during swarm time. This phenomenon implies a sophisticated context- and time-dependent modulation of mosquito audition, the mechanisms of which are largely unknown. Using transcriptomics, we identify a complex network of candidate neuromodulators regulating mosquito hearing in the species Anopheles gambiae. Among them, octopamine stands out as an auditory modulator during swarm time. In-depth analysis of octopamine auditory function shows that it affects the mosquito ear on multiple levels: it modulates the tuning and stiffness of the flagellar sound receiver and controls the erection of antennal fibrillae. We show that two α- and β-adrenergic-like octopamine receptors drive octopamine’s auditory roles and demonstrate that the octopaminergic auditory control system can be targeted by insecticides. Our findings highlight octopamine as key for mosquito hearing and mating partner detection and as a potential novel target for mosquito control.

Hitting the right note at the right time: Circadian control of audibility in Anopheles mosquito mating swarms is mediated by flight tones.

Mating swarms of malaria mosquitoes form every day at sunset throughout the tropical world. They typically last less than 30 minutes. Activity must thus be highly synchronized between the sexes. Moreover, males must identify the few sporadically entering females by detecting the females’ faint flight tones. We show that the Anopheles circadian clock not only ensures a tight synchrony of male and female activity but also helps sharpen the males’ acoustic detection system: By raising their flight tones to 1.5 times the female flight tone, males enhance the audibility of females, specifically at swarm time. Previously reported “harmonic convergence” events are only a random by-product of the mosquitoes’ flight tone variance and not a signature of acoustic interaction between males and females. The flight tones of individual mosquitoes occupy narrow, partly non-overlapping frequency ranges, suggesting that the audibility of individual females varies across males.

Harmonic convergence coordinates swarm mating by enhancing mate detection in the malaria mosquito Anopheles gambiae

The mosquito Anopheles gambiae is a major African malaria vector, transmitting parasites responsible for significant mortality and disease burden. Although flight acoustics are essential to mosquito mating and present promising alternatives to insecticide-based vector control strategies, there is limited data on mosquito flight tones during swarming. Here, for the first time, we present detailed analyses of free-flying male and female An. gambiae flight tones and their harmonization (harmonic convergence) over a complete swarm sequence. Audio analysis of single-sex swarms showed synchronized elevation of male and female flight tones during swarming. Analysis of mixed-sex swarms revealed additional 50 Hz increases in male and female flight tones due to mating activity. Furthermore, harmonic differences between male and female swarm tones in mixed-sex swarms and in single-sex male swarms with artificial female swarm audio playback indicate that frequency differences of approximately 50 Hz or less at the male second and female third harmonics (M2:F3) are maintained both before and during mating interactions. This harmonization likely coordinates male scramble competition by maintaining ideal acoustic recognition within mating pairs while acoustically masking phonotactic responses of nearby swarming males to mating females. These findings advance our knowledge of mosquito swarm acoustics and provide vital information for reproductive control strategies.

Male and Female Mosquito (Diptera: Culicidae) Attraction to Sound and Its Relevance to Potential Applications in Vector Surveillance

Abstract Mosquito hearing is a complex process primarily involved in intraspecific communication between males and females. Although mosquitoes previously were believed to possess a relatively rudimentary auditory system, we now know that they can hear sounds at greater distances and process sounds through an efferent pathway, similar to vertebrates. In mating swarms, mosquitoes use acoustic signals created by conspecific wingbeats to locate and respond to one another through harmonic convergence. Male capture is an emerging area of interest for monitoring sterile insect release programs, and numerous studies have explored using female flight tones (wing-beat frequencies) to attract and capture male mosquitoes by altering or developing novel acoustic traps. It is also important to consider sound pattern, volume, and sound pressure levels of broadcasted noises, as well as implementing other attractive cues, such as swarm markers, to acoustic traps to increase success in the field. Female attraction to sound-baited traps has also been explored in the laboratory and field, using frequencies similar to male wing-beats and stereotypical vertebrate host calls, such as frogs and birds. In this review, the physiological and behavioral aspects of mosquito hearing are explored, as well as the importance of acoustic signals for mate choice and successful mating. The use of acoustic traps for male and female capture are discussed, as well as the implications for vector surveillance, and the limitations to using these traps.

The Effect of the Acoustic Swarm Environment on the Behaviour and Hearing of Male Culex quinquefasciatus Mosquitoes

Background The mating behaviour of many mosquito species is mediated by sound: males pursue and mate with a female mid-flight by using their antennae to detect and track the whine of the female flight-tone. Upon detection of the female's flight-tones (or artificial female-like tones), males track the sound source and display stereotypical rapid frequency modulation (RFM) acoustic behaviour when very close to the female. Under natural conditions, flying males of these mosquito species form relatively dense agglomerations – swarms – while waiting for sexually receptive females to pass nearby. Individual male mosquitoes thus face intense competition to detect, track, and access a passing female. Aims We aim to understand the significance of the swarm acoustics on the individual mating behaviour of male mosquitoes. Specifically, we tested the influence of simulated swarm sound on the RFM behaviour and on the hearing physiology of male mosquitoes. Methods We derived the behavioural threshold responses of individual male mosquitoes exposed to female-like tones with and without the presence of a banded 700-900 Hz synthesised swarm sound. Two electrophysiological experiments were also performed: 1) measurement of the threshold of the mosquito auditory organ, the Johnston's organ (JO), to female-like tones with and without swarm sound; 2) measurement from the JO of electrical difference-tone distortion products generated by tones at the frequencies of the male and female flight tones. Results Behavioural experiments with free-flying mosquitoes and electrophysiological preparations indicate that swarm sound has no apparent affect on the behavioural and hearing thresholds of males for female-like sounds. Conclusion This indicates that from an individual male mosquito perspective, swarms are not a source of acoustic noise and males are neither facilitated nor impaired by synthetic swarm noise in detecting females. Furthermore, the swarm noise does not appear to impair or facilitate the ability of males to detect their own flight tones and those of nearby male mosquitoes.

Flight tone characterisation of the South American malaria vector Anopheles darlingi (Diptera: Culicidae).

BACKGROUND Flight tones play important roles in mosquito reproduction. Several mosquito species utilise flight tones for mate localisation and attraction. Typically, the female wingbeat frequency (WBF) is lower than males, and stereotypic acoustic behaviors are instrumental for successful copulation. Mosquito WBFs are usually an important species characteristic, with female flight tones used as male attractants in surveillance traps for species identification. Anopheles darlingi is an important Latin American malaria vector, but we know little about its mating behaviors.OBJECTIVES We characterised An. darlingi WBFs and examined male acoustic responses to immobilised females.METHODS Tethered and free flying male and female An. darlingi were recorded individually to determine their WBF distributions. Male-female acoustic interactions were analysed using tethered females and free flying males.FINDINGS Contrary to most mosquito species, An. darlingi females are smaller than males. However, the male’s WBF is ~1.5 times higher than the females, a common ratio in species with larger females. When in proximity to a female, males displayed rapid frequency modulations that decreased upon genitalia engagement. Tethered females also modulated their frequency upon male approach, being distinct if the interaction ended in copulation or only contact.MAIN CONCLUSIONS This is the first report of An. darlingi flight acoustics, showing that its precopulatory acoustics are similar to other mosquitoes despite the uncommon male:female size ratio, suggesting that WBF ratios are common communication strategies rather than a physical constraint imposed by size.

Assessing the acoustic behaviour of Anopheles gambiae (s.l.) dsxF mutants: implications for vector control

BackgroundRelease of gene-drive mutants to suppress Anopheles mosquito reproduction is a promising method of malaria control. However, many scientific, regulatory and ethical questions remain before transgenic mosquitoes can be utilised in the field. At a behavioural level, gene-drive carrying mutants should be at least as sexually attractive as the wildtype populations they compete against, with a key element of Anopheles copulation being acoustic courtship. We analysed sound emissions and acoustic preference in a doublesex mutant previously used to collapse Anopheles gambiae (s.l.) cages.MethodsAnopheles rely on flight tones produced by the beating of their wings for acoustic mating communication. We assessed the impact of disrupting a female-specific isoform of the doublesex gene (dsxF) on the wing beat frequency (WBF; measured as flight tone) of males (XY) and females (XX) in homozygous dsxF− mutants (dsxF−/−), heterozygous dsxF− carriers (dsxF+/−) and G3 dsxF+ controls (dsxF+/+). To exclude non-genetic influences, we controlled for temperature and wing length. We used a phonotaxis assay to test the acoustic preferences of mutant and control mosquitoes.ResultsA previous study showed an altered phenotype only for dsxF−/− females, who appear intersex, suggesting that the female-specific dsxF allele is haplosufficient. We identified significant, dose-dependent increases in the WBF of both dsxF−/− and dsxF+/− females compared to dsxF+/+ females. All female WBFs remained significantly lower than male equivalents, though. Males showed stronger phonotactic responses to the WBFs of control dsxF+/+ females than to those of dsxF+/− and dsxF−/− females. We found no evidence of phonotaxis in any female genotype. No male genotypes displayed any deviations from controls.ConclusionsA prerequisite for anopheline copulation is the phonotactic attraction of males towards female flight tones within mating swarms. Reductions in mutant acoustic attractiveness diminish their mating efficiency and thus the efficacy of population control efforts. Caged population assessments may not successfully reproduce natural mating scenarios. We propose to amend existing testing protocols to better reflect competition between mutants and target populations. Our findings confirm that dsxF disruption has no effect on males; for some phenotypic traits, such as female WBFs, the effects of dsxF appear dose-dependent rather than haplosufficient.

Buzzkill: targeting the mosquito auditory system.

Sound plays an important role in mosquito sensory ecology. Acoustic perception and acoustically driven behaviours therefore represent potentially effective control targets. Previous scientific efforts around acoustic-based control and surveillance have not been systematic and ambiguity around the exact role of acoustic communication in conspecific interactions remains. Here, we briefly review recent advances in mosquito auditory physiology and behavioural ecology as well as ongoing activities to incorporate sound into control and surveillance tools. We highlight areas where increased collaboration between physiologists, molecular biologists, behavioural ecologists and control experts is needed to capitalize on this progress and realize the potential of sound-based technologies and strategies.

Precopulatory acoustic interactions of the New World malaria vector Anopheles albimanus (Diptera: Culicidae)

BackgroundAnopheles albimanus is a malaria vector in Central America, northern South America and the Caribbean. Although a public health threat, An. albimanus precopulatory mating behaviors are unknown. Acoustics play important roles in mosquito communication, where flight tones allow males to detect and attract potential mates. The importance of sound in precopulatory interactions has been demonstrated in Toxorhynchites brevipalpis, Aedes aegypti, Culex quinquefasciatus and Anopheles gambiae; convergence in a shared harmonic of the wing beat frequency (WBF) during courtship is thought to increase the chance of copulation. To our knowledge, An. albimanus precopulatory acoustic behaviors have not been described to date. Here, we characterized An. albimanus (i) male and female flight tones; (ii) male–female precopulatory acoustic interactions under tethered and free flight conditions; and (iii) male-male acoustic interactions during free flight.ResultsWe found significant increases in the WBFs of both sexes in free flight compared to when tethered. We observed harmonic convergence between 79% of tethered couples. In free flight, we identified a female-specific behavior that predicts mate rejection during male mating attempts: females increase their WBFs significantly faster during mate rejection compared to a successful copulation. This behavior consistently occurred during mate rejection regardless of prior mating attempts (from the same or differing male). During group flight, males of An. albimanus displayed two distinct flying behaviors: random flight and a swarm-like, patterned flight, each associated with distinct acoustic characteristics. In the transition from random to patterned flight, males converged their WBFs and significantly decreased flight area, male-male proximity and the periodicity of their trajectories.ConclusionsWe show that tethering of An. albimanus results in major acoustic differences compared to free flight. We identify a female-specific behavior that predicts mate rejection during male mating attempts in this species and show that male groups in free flight display distinct flying patterns with unique audio and visual characteristics. This study shows that An. albimanus display acoustic features identified in other mosquito species, further suggesting that acoustic interactions provide worthwhile targets for mosquito intervention strategies. Our results provide compelling evidence for swarming in this species and suggests that acoustic signaling is important for this behavior.

The Long and Short of Hearing in the Mosquito Aedes aegypti

Mating behavior in Aedes aegypti mosquitoes occurs mid-air and involves the exchange of auditory signals at close range (millimeters to centimeters) [1-6]. It is widely assumed that this intimate signaling distance reflects short-range auditory sensitivity of their antennal hearing organs to faint flight tones [7, 8]. To the contrary, we show here that male mosquitoes can hear the female's flight tone at surprisingly long distances-from several meters to up to 10 m-and that unrestrained, resting Ae. aegypti males leap off their perches and take flight when they hear female flight tones. Moreover, auditory sensitivity tests of Ae. aegypti's hearing organ, made from neurophysiological recordings of the auditory nerve in response to pure-tone stimuli played from a loudspeaker, support the behavioral experiments. This demonstration of long-range hearing in mosquitoes overturns the common assumption that the thread-like antennal hearing organs of tiny insects are strictly close-range ears. The effective range of a hearing organ depends ultimately on its sensitivity [9-13]. Here, a mosquito's antennal ear is shown to be sensitive to sound levels down to 31 dB sound pressure level (SPL), translating to air particle velocity at nanometer dimensions. We note that the peak of energy of the first formant of the vowels of the human speech spectrum range from about 200-1,000Hz and is typically spoken at 45-70 dB SPL; together, they lie in the sweet spot of mosquito hearing. VIDEO ABSTRACT.

Masking of an auditory behaviour reveals how male mosquitoes use distortion to detect females.

The mating behaviour of many mosquito species is mediated essentially by sound: males follow and mate with a female mid-flight by detecting and tracking the whine of her flight-tones. The stereotypical rapid frequency modulation (RFM) male behaviour, initiated in response to the detection of the female's flight-tones, has provided a means of investigating these auditory mechanisms while males are free-flying. Mosquitoes hear with their antennae, which vibrate to near-field acoustic excitation. The antennae generate nonlinear vibrations (distortion products, DPs) at frequencies that are equal to the difference between the two simultaneously presented tones, e.g. the male and female flight-tones, which are detected by mechanoreceptors in the auditory Johnston's organ (JO) at the base of the antenna. Recent studies indicated the male mosquito's JO is tuned not to the female flight-tone, but to the frequency difference between the male and female flight-tones. To test the hypothesis that mosquitoes detect this frequency difference, Culex quinquefasciatus males were presented simultaneously with a female flight-tone and a masking tone, which should suppress the male's RFM response to sound. The free-flight behavioural and in vivo electrophysiological experiments revealed that acoustic masking suppresses the RFM response to the female's flight-tones by attenuating the DPs generated in the nonlinear vibration of the antennae. These findings provide direct evidence in support of the hypothesis that male mosquitoes detect females when both are in flight through difference tones generated in the vibrations of their antennae owing to the interaction between their own flight-tones and those of a female.

Frequency organization of the Johnston's organ in male mosquitoes (Diptera, Culicidae).

The Johnston's organs (JO) of mosquitoes are the most complex mechanosensitive organs yet found in insects. Previous findings on the behavior of mosquitoes suggest that, together with exceptional sensitivity, their auditory system can discriminate frequencies. Analysis of compound responses of the JO did not provide unambiguous evidence of such discrimination, nor did it help to find its mechanism. Using the feedback stimulation method, we measured the tuning frequencies of the JO sensory neurons. Here we present electrophysiological evidence that male mosquitoes of Culex pipiens possess at least eight groups of auditory neurons that are distinct in their frequency tuning, with individual frequencies ranging from 85 to 470 Hz. Most of the neurons are tuned to 190-270 Hz, which corresponds to the difference between male and female flight tones. Axons of the JO sensory units propagate graded amplified receptor potentials rather than all-or-none action potentials, are grouped into pairs or triplets and often respond in anti-phase to each other. Some features of the mosquito auditory system suggest an analogy to the retinal mechanisms. Together with our previous findings on frequency tuning in female mosquitoes of different species, this study presents evidence in favor of sophisticated frequency analysis of sound in mosquitoes.

The Siren's Song: Exploitation of Female Flight Tones to Passively Capture Male Aedes aegypti (Diptera: Culicidae).

The need to capture male mosquitoes has intensified recently as a result of a number of male-based sterile insect technique (SIT) and population-modification programs focused on Aedes aegypti (L.) having initiated field releases. Here, we report the results of the successful exploitation of the attraction of male Ae. aegypti to female flight tones to enhance male collections in nonmechanical passive (nonbattery powered) Gravid Aedes Traps (GAT). Prior to field studies, male attraction to female flight tones of 484 and 560 Hz, as well as to a male flight tone of 715 Hz, were assessed in a series of controlled release-recapture and semifield trials. These trials determined that a pure tone of 484 Hz was significantly more attractive to free-flying males than the other flight tones and enabled their collection in sound-baited GATs (ca. 95% capture rate after 2 h; 484 Hz at 65 dB). In contrast, gravid females were unresponsive to male or female flight tones and were evenly distributed among sound-baited and control GATs. Importantly, under normal field conditions sound-baited GATs (484 Hz at 70 dB) captured significantly more male Ae. aegypti per 24-h trap interval (1.3 ± 0.37) than controls (0.2 ± 0.13). Overall, sound-bated GATs captured approximately twice as many Ae. aegypti (male and female; 3.0 ± 0.68 per interval, 30 total) than controls (1.5 ± 0.56 per interval, 15 total). These results reveal that sound-baited GATs are a simple and effective surveillance tool for Ae. aegypti that would allow current male-based SIT and population-modification programs to effectively monitor males in their target populations.

Determinants of Male <I>Aedes aegypti</I> and <I>Aedes polynesiensis</I> (Diptera: Culicidae) Response to Sound: Efficacy and Considerations for Use of Sound Traps in the Field

Understanding the mating competitiveness of male mosquitoes in field settings is essential to programs relying on the mass release of modified male mosquitoes, yet studies on male ecology have been hampered by the lack of a convenient trapping method. An existing promising method makes use of the innate attraction of males to female flight tones. Here, we present laboratory, greenhouse, and field experiments on the efficacy of sound traps for the collection of Aedes aegypti (L.) and Aedes polynesiensis Marks, and laboratory experiments with Ae. aegypti on the effects of male age, size, and mating status on responsiveness to a range of frequencies. Age and mating status influenced the overall responsiveness to sound, whereas male size did not. There were no interactions between these factors and sound frequency. A Centers for Disease Control and Prevention miniature light trap modified to produce a tone of 465 Hz collected 76.2% of Ae. aegypti males in laboratory cages, and 49.7% of males in a greenhouse enclosure. In two sets of experiments in laboratory cages, 50.8 and 46.5% of male Ae. polynesiensis were captured with a trap producing a tone of 440 Hz. In the field, CDC miniature light traps or BG-Sentinel traps fitted with a portable speaker producing tones of 440 or 465 Hz captured significantly more male Ae. polynesiensis when placed near a male swarm than did traps that did not produce sound. When the trap was placed at a distance of 16.5 m from the nearest swarm, there was no significant difference in the number of males caught between control and sound-producing traps. The numbers of Ae. aegypti males captured were low under all circumstances in the field.

Structure and function of the Johnston’s organ in Fleuria lacustris Kieff. males (Diptera, Chironomidae)

The majority of chironomid midges mate in swarms, where males find females by their flight sounds using specialized Johnston’s organs for acoustic perception. Males of Fleuria lacustris do not swarm and copulate on the ground. Both the flagellum and antennal fibrils are shortened and the pedicel is reduced in comparison with that typical of swarming midge species. Our results demonstrate that, in swarming midge species, the number of antennal fibrils and of A-type chordotonal sensilla in the male Johnston’s organ is by 1.33 and by 21 times higher, respectively, than in F. lacustris. Though Johnston’s organ of the latter species responds to female flight tones, it is significantly (about 70 times) less sensitive to these stimuli in comparison with the Johnston’s organ of swarming species. The decrease in the sensitivity of the Johnston’s organ in F. lacustris can be explained by the decrease in the size and the number of antennal structures, whereas their ability to perceive acoustic signals is determined by the presence of a relatively high number of A-type sensilla. Our results demonstrate that F. lacustris males are not able to search for conspecific females by perception of acoustic signals produced during the flight; however, it cannot be ruled out that females produce sounds during copulation on the substrate and thus affect male behavior.

Sex Recognition through Midflight Mating Duets in Culex Mosquitoes Is Mediated by Acoustic Distortion

Sexual recognition through wing-beat frequency matching was first demonstrated in Toxorhynchites brevipalpis, where wing-beat frequencies of males and females are similar. Here we show frequency matching in Culex quinquefasciatus, where the wing-beat frequencies of males and females differ considerably. The wing-beat frequencies converge not on the fundamental but on the nearest shared harmonic (usually female's third and male's second). Frequencies in this range are, however, too high to elicit phasic sensory-neural responses from the Johnston's organ (JO) or to drive the mosquito's motor neurons. Potential cues for frequency matching are difference tones produced by nonlinear mixing of male and female flight tones in the vibrations of the mosquito's antennae. Receptor potentials and neural-motor activity were recorded in response to difference tones produced when a mosquito was stimulated simultaneously by two tones at frequencies outside the phasic response range of the JO but within range of the antennal vibrations. We demonstrate sexual recognition through matching of flight-tone harmonics in Culex mosquitoes and suggest that difference tones are used as an error signal for frequency matching beyond the frequency range of the JO's sensory-neural range. This is the first report of acoustic distortion being exploited as a sensory cue, rather than existing as an epiphenomenon.

Flying in Tune: Sexual Recognition in Mosquitoes

Mosquitoes hear with their antennae, which in most species are sexually dimorphic. Johnston, who discovered the mosquito auditory organ at the base of the antenna 150 years ago, speculated that audition was involved with mating behaviour. Indeed, male mosquitoes are attracted to female flight tones. The male auditory organ has been proposed to act as an acoustic filter for female flight tones, but female auditory behavior is unknown. We show, for the first time, interactive auditory behavior between males and females that leads to sexual recognition. Individual males and females both respond to pure tones by altering wing-beat frequency. Behavioral auditory tuning curves, based on minimum threshold sound levels that elicit a change in wing-beat frequency to pure tones, are sharper than the mechanical tuning of the antennae, with males being more sensitive than females. We flew opposite-sex pairs of tethered Toxorhynchites brevipalpis and found that each mosquito alters its wing-beat frequency in response to the flight tone of the other, so that within seconds their flight-tone frequencies are closely matched, if not completely synchronized. The flight tones of same-sex pairs may converge in frequency but eventually diverge dramatically.