Behavioural analysis of swarming mosquitoes reveals high hearing sensitivity in Anopheles coluzzii.

Mosquitoes of many species mate in station-keeping swarms. Mating chases ensue as soon as a male detects the flight tones of a female with his auditory organs. Previous studies of hearing thresholds have mainly used electrophysiological methods that prevent the mosquito from flying naturally. The main aim of this study was to quantify behaviourally the sound level threshold at which males can hear females. Free-flying male Anopheles coluzzii were released in a large arena (∼2 m high×2 m×1 m) with a conspicuous object on the ground that stimulated swarming behaviour. Males were exposed to a range of natural and synthetic played-back sounds of female flight. We monitored the responses of males and their distance to the speaker by recording changes in their wingbeat frequency and angular speed. We show that the mean male behavioural threshold of particle velocity hearing lies between 13 and 20 dB sound particle velocity level (SVL) (95% confidence interval). A conservative estimate of 20 dB SVL (i.e. <0.5 µm s-1 particle velocity) is 12-26 dB lower than most of the published electrophysiological measurements from the Johnston's organ. In addition, we suggest that (1) the first harmonic of a female's flight sound is sufficient for males to detect her presence, (2) males respond with a greater amplitude to single-female sounds than to the sound of a group of females and (3) the response of males to the playback of the flight sound of a live female is the same as to that of a recorded sound of constant frequency and amplitude.

Perceptual equivalence of the Liljencrants-Fant and linear-filter glottal flow models.

Speech glottal flow has been predominantly described in the time-domain in past decades, the Liljencrants-Fant (LF) model being the most widely used in speech analysis and synthesis, despite its computational complexity. The causal/anti-causal linear model (LFCALM) was later introduced as a digital filter implementation of LF, a mixed-phase spectral model including both anti-causal and causal filters to model the vocal-fold open and closed phases, respectively. To further simplify computation, a causal linear model (LFLM) describes the glottal flow with a fully causal set of filters. After expressing these three models under a single analytic formulation, we assessed here their perceptual consistency, when driven by a single parameter Rd related to voice quality. All possible paired combinations of signals generated using six Rd levels for each model were presented to subjects who were asked whether the two signals in each pair differed. Model pairs LFLM-LFCALM were judged similar when sharing the same Rd value, and LF was considered the same as LFLM and LFCALM given a consistent shift in Rd. Overall, the similarity between these models encourages the use of the simpler and more computationally efficient models LFCALM and LFLM in speech synthesis applications.

Drawing melodies: evaluation of chironomic singing synthesis.

Cantor Digitalis, a real-time formant synthesizer controlled by a graphic tablet and a stylus, is used for assessment of melodic precision and accuracy in singing synthesis. Melodic accuracy and precision are measured in three experiments for groups of 20 and 28 subjects. The task of the subjects is to sing musical intervals and short melodies, at various tempi, using chironomy (hand-controlled singing), mute chironomy (without audio feedback), and their own voices. The results show the high accuracy and precision obtained by all the subjects for chironomic control of singing synthesis. Some subjects performed significantly better in chironomic singing compared to natural singing, although other subjects showed comparable proficiency. For the chironomic condition, mean note accuracy is less than 12 cents and mean interval accuracy is less than 25 cents for all the subjects. Comparing chironomy and mute chironomy shows that the skills used for writing and drawing are used for chironomic singing, but that the audio feedback helps in interval accuracy. Analysis of blind chironomy (without visual reference) indicates that a visual feedback helps greatly in both note and interval accuracy and precision. This study demonstrates the capabilities of chironomy as a precise and accurate mean for controlling singing synthesis.

Protocol for rearing and using mosquitoes for flight path tracking and behavioral characterization in wind tunnel bioassays.

Mosquito behavioral assays are an important component in vector research and control tool development. Here, we present a protocol for rearing Anopheles mosquitoes, performing host-seeking behavioral bioassays, and collecting 3D flight tracks in a large wind tunnel. We describe steps for setting up host-seeking landing assays, both as a non-choice and as a dual-choice assay, and analyzing flight tracks. This protocol can be applied in the research of several behavioral traits, including nectar seeking, resting, mating, and oviposition behavior. For complete details on the use and execution of this protocol, please refer to Carnaghi et al.1.

Visual and thermal stimuli modulate mosquito-host contact with implications for improving malaria vector control tools.

Malaria prevention relies on mosquito control interventions that use insecticides and exploit mosquito behavior. The rise of insecticide resistance and changing transmission dynamics urgently demand vector control innovation. To identify behavioral traits that could be incorporated into such tools, we investigated the flight and landing response of Anopheles coluzzii to human-like host cues. We show that landing rate is directly proportional to the surface area of thermal stimulus, whereas close-range orientation is modulated by both thermal and visual inputs. We modeled anopheline eye optics to theorize the distance at which visual targets can be detected under a range of conditions, and experimentally established mosquito preference for landing on larger targets, although landing density is greater on small targets. Target orientation does not affect landing rate; however, vertical targets can be resolved at greater distance than horizontal targets of the same size. Mosquito traps for vector control could be significantly enhanced by incorporating these features.

Mosquito sound communication: are male swarms loud enough to attract females?

Given the unsurpassed sound sensitivity of mosquitoes among arthropods and the sound source power required for long-range hearing, we investigated the distance over which female mosquitoes detect species-specific cues in the sound of station-keeping mating swarms. A common misunderstanding, that mosquitoes cannot hear at long range because their hearing organs are 'particle-velocity' receptors, has clouded the fact that particle velocity is an intrinsic component of sound whatever the distance to the sound source. We exposed free-flying Anopheles coluzzii females to pre-recorded sounds of male An. coluzzii and An. gambiae s.s. swarms over a range of natural sound levels. Sound levels tested were related to equivalent distances between the female and the swarm for a given number of males, enabling us to infer distances over which females might hear large male swarms. We show that females do not respond to swarm sound up to 48 dB sound pressure level (SPL) and that louder SPLs are not ecologically relevant for a swarm. Considering that swarms are the only mosquito sound source that would be loud enough to be heard at long range, we conclude that inter-mosquito acoustic communication is restricted to close-range pair interactions. We also showed that the sensitivity to sound in free-flying males is much enhanced compared to that of tethered ones.