Wing Vibration Research Articles

Vibration and sound of an elastic wing actuated at its leading edge

The motion and sound of a thin elastic plate, subject to uniform low-Mach flow and actuated at its leading edge, is studied. The linearized response to arbitrary small-amplitude translation and rotation is analyzed using Fourier decomposition of the forcing signal. Both periodic (sinusoidal) and non-periodic (“step-jump”) actuations are investigated. When the frequency spectrum of the forcing signal contains an eigenfrequency Ω res of the unforced system, a resonance motion is excited and the plate oscillates at the corresponding eigenmode. The dynamical description is applied to formulate the acoustic problem, where the sources of sound include the plate velocity and fluid vorticity. Acoustic radiation of a dipole type is calculated and discussed in the limit where the plate is acoustically compact. In the case of sinusoidal excitation, plate elasticity has two opposite effects on sound radiation, depending on the forcing frequency: at frequencies close to Ω res , the near-resonance motion results in the generation of high sound levels; however, at frequencies far from Ω res , plate elasticity reduces the amplitude of plate deflection (compared to that of a rigid plate), leading to noise reduction. In the case of non-periodic actuation, the plate-fluid system amplifies those frequencies that are closest to Ω res , which, in turn, dominate the acoustic signature. The results identify the trailing edge noise as the main source of sound, dominating the sound generated by direct plate motion. We suggest the present theory as a preliminary tool for examining the acoustic signature of flapping flight, common in insects and flapping micro-air-vehicles.

The genomic response to courtship song stimulation in female Drosophila melanogaster.

Courtship behaviour involves a complex exchange of signals and responses. These are usually studied at the phenotypic level, and genetic or transcriptional responses to courtship are still poorly understood. Here, we examine the gene-expression changes in Drosophila melanogaster females in response to one of the key male courtship signals in mate recognition, song produced by male wing vibration. Using long oligonucleotide microarrays, we identified several genes that responded differentially to the presence or absence of acoustic courtship stimulus. These changes were modest in both the number of genes involved and fold-changes, but notably dominated by antennal signalling genes involved in olfaction as well as neuropeptides and immune response genes. Second, we compared the expression patterns of females stimulated with synthetic song typical of either conspecific or heterospecific (Drosophila simulans) males. In this case, antennal olfactory signalling and innate immunity genes were also enriched among the differentially expressed genes. We confirmed and investigated the time course of expression differences of two identified immunity genes using real-time quantitative PCR. Our results provide novel insight into specific molecular changes in females in response to courtship song stimulation. These may be involved in both signal perception and interpretation and some may anticipate molecular interactions that occur between the sexes after mating.

Flow-induced vibrations of low aspect ratio rectangular membrane wings

An experimental study of a low aspect ratio rectangular membrane wing in a wind tunnel was conducted for a Reynolds number range of 2.4×10 4–4.8×10 4. Time-accurate measurements of membrane deformation were combined with the flow field measurements. Analysis of the fluctuating deformation reveals chordwise and spanwise modes, which are due to the shedding of leading-edge vortices as well as tip vortices. At higher angles of attack, the second mode in the chordwise direction becomes dominant as the vortex shedding takes place. The dominant frequencies of the membrane vibrations are similar to those of two-dimensional membrane airfoils. Measured frequency of vortex shedding from the low aspect ratio rigid wing suggests that membrane vibrations occur at the natural frequencies close to the harmonics of the wake instabilities. Vortex shedding frequency from rigid wings shows remarkably small effect of aspect ratio even when it is as low as unity.

Sound radiation and wing mechanics in stridulating field crickets (Orthoptera: Gryllidae)

Male field crickets emit pure-tone mating calls by rubbing their wings together. Acoustic radiation is produced by rapid oscillations of the wings, as the right wing (RW), bearing a file, is swept across the plectrum borne on the left wing (LW). Earlier work found the natural resonant frequency (f(o)) of individual wings to be different, but there is no consensus on the origin of these differences. Previous studies suggested that the frequency along the song pulse is controlled independently by each wing. It has also been argued that the stridulatory file has a variable f(o) and that the frequency modulation observed in most species is associated with this variability. To test these two hypotheses, a method was developed for the non-contact measurement of wing vibrations during singing in actively stridulating Gryllus bimaculatus. Using focal microinjection of the neuroactivator eserine into the cricket's brain to elicit stridulation and micro-scanning laser Doppler vibrometry, we monitored wing vibration in actively singing insects. The results show significantly lower f(o) in LWs compared with RWs, with the LW f(o) being identical to the sound carrier frequency (N=44). But during stridulation, the two wings resonate at one identical frequency, the song carrier frequency, with the LW dominating in amplitude response. These measurements also demonstrate that the stridulatory file is a constant resonator, as no variation was observed in f(o) along the file during sound radiation. Our findings show that, as they engage in stridulation, cricket wings work as coupled oscillators that together control the mechanical oscillations generating the remarkably pure species-specific song.

How do honeybees attract nestmates using waggle dances in dark and noisy hives?

It is well known that honeybees share information related to food sources with nestmates using a dance language that is representative of symbolic communication among non-primates. Some honeybee species engage in visually apparent behavior, walking in a figure-eight pattern inside their dark hives. It has been suggested that sounds play an important role in this dance language, even though a variety of wing vibration sounds are produced by honeybee behaviors in hives. It has been shown that dances emit sounds primarily at about 250–300 Hz, which is in the same frequency range as honeybees' flight sounds. Thus the exact mechanism whereby honeybees attract nestmates using waggle dances in such a dark and noisy hive is as yet unclear. In this study, we used a flight simulator in which honeybees were attached to a torque meter in order to analyze the component of bees' orienting response caused only by sounds, and not by odor or by vibrations sensed by their legs. We showed using single sound localization that honeybees preferred sounds around 265 Hz. Furthermore, according to sound discrimination tests using sounds of the same frequency, honeybees preferred rhythmic sounds. Our results demonstrate that frequency and rhythmic components play a complementary role in localizing dance sounds. Dance sounds were presumably developed to share information in a dark and noisy environment.

Animal Communication: Flies' Ears Are Tuned In

Male fruit flies sing to females with quiet, close-range wing vibrations. A new study has found that the flies' antennal ears show active tuning to the species-specific frequencies of songs.

Neuronal Control of Drosophila Courtship Song

The courtship song of the Drosophila male serves as a genetically tractable model for the investigation of the neural mechanisms of decision-making, action selection, and motor pattern generation. Singing has been causally linked to the activity of the set of neurons that express the sex-specific fru transcripts, but the specific neurons involved have not been identified. Here we identify five distinct classes of fru neuron that trigger or compose the song. Our data suggest that P1 and pIP10 neurons in the brain mediate the decision to sing, and to act upon this decision, while the thoracic neurons dPR1, vPR6, and vMS11 are components of a central pattern generator that times and shapes the song's pulses. These neurons are potentially connected in a functional circuit, with the descending pIP10 neuron linking the brain and thoracic song centers. Sexual dimorphisms in each of these neurons may explain why only males sing.

Sound production during agonistic behavior of male Drosophila melanogaster

Male Drosophila fruitflies acquire and defend territories in order to attract females for reproduction. Both, male-directed agonistic behavior and female-directed courtship consist of series of recurrent stereotypical components. Various studies demonstrated the importance of species-specific sound patterns generated by wing vibration as being critical for male courtship success. In this study we analyzed the patterns and importance of sound signals generated during agonistic interactions of male Drosophila melanogaster. In contrast to acoustic courtship signals that consist of sine and pulse patterns and are generated by one extended wing, agonistic signals lack sine-like components and are generally produced by simultaneous movements of both wings. Though intra-pulse oscillation frequencies (carrier frequency) are identical, inter-pulse intervals are twice as long and more variable in aggression signals than in courtship songs, where their precise temporal pattern serves species recognition. Acoustic signals accompany male agonistic interactions over their entire course but occur particularly often after tapping behavior which is a major way to identify the gender of the interaction partner. Since similar wing movements may either be silent or generate sound and wing movements with sound have a greater impact on the subsequent behavior of a receiver, sound producing wing movements seem to be generated intentionally to serve as a specific signal during fruit fly agonistic encounters.

Resonant Sound Production inCopiphora gorgonensis(Tettigoniidae: Copiphorini), an Endemic Species fromParque Nacional Natural Gorgona, Colombia

This article describes the acoustic characters of Copiphora gorgonensis, a new species endemic to Gorgona Island National Park, Colombia. It is closely related to C. brevicauda, a congener distributed in the Pacific rainforest of Ecuador and Colombia, and also reported in Central America and other countries of northern South America. Here we provide diagnostic characters for identification; we study the mechanics of stridulation using laser vibrometry and optical motion detectors. Distinguishing features include: the highly tonal song of males with a carrier frequency peaking at 23 kHz; pulses repeated with a high rate of nearly 50/s and wing motion exhibiting a typical subsinusoidal pattern, as has been described for other Copiphorini. The natural frequency of the right forewing is close to that of the calling song and the wing-motion patterns indicate that sound vibrations are the result of sustained tooth impacts, corresponding to the natural frequency of wing vibration, i.e., the tonal characteristic of the calling song in this species is the result of resonant stridulation. This resonance, and the amplitude component of the song, are attributed to the mirror frame and its surrounding cells and veins. These results are contrasted and discussed in regard to published literature on tettigoniid stridulation.

Genetic Feminization of the Thoracic Nervous System Disrupts Courtship Song in Male Drosophila melanogaster

: Despite the growing research investigating the sex-specific organization of courtship behavior in Drosophila melanogaster, much remains to be understood about the sex-specific organization of the motor circuit that drives this behavior. To investigate the sex-specification of a tightly patterned component of courtship behavior, courtship song, the authors used the GAL4/UAS targeted gene expression system to feminize the ventral ganglia in male Drosophila and analyzed the acoustic properties of courtship song. More specifically, the authors used the thoracic-specifying teashirt promoter (tshGAL4) to express feminizing transgenes specifically in the ventral ganglia. When tshGAL4 drove expression of transformer (tra), males were unable to produce prolonged wing extensions. Transgenic expression of an RNAi construct directed against male-specific fruitless (fruM) transcripts resulted in normal wing extension, but highly defective courtship song, with 58% of males failing to generate detectable courtship song. Of those that did sing, widths of individual pulses were significantly broader than controls, suggesting thoracic fruM function serves to mediate proprioceptive-dependent wing vibration damping during pulse song. However, the most critical signal in the song, the interpulse interval, remained intact. The inability to phenocopy this effect by reducing fruM expression in motor neurons and proprioceptive neurons suggests thoracic interneurons require fruM for proper pulse song execution and patterning of pulse structure, but not for pulse timing. This provides evidence that genes establishing sex-specific activation of complex behaviors may also be used in establishing pattern-generating motor networks underlying these sex-specific behaviors.

A comprehensive finite element model for tapered composite wing structures

A comprehensive finite element model incorporating the features of comprehensive wing model and finite element method is developed in this paper. This new model extends the applicability of comprehensive wing model from uniform composite wings to tapered composite wings. It preserves the simplicity of one-dimensional finite element but performs like three-dimensional finite element for wing structural analysis. To verify its accuracy and show its efficiency, this model which is applicable to the general dynamic analysis is reduced to two simple cases: static analysis and free vibration analysis. Based upon the reduction results for static and free vibration cases, several numerical examples of composite wing structures are presented such as tapered wings subjected to end load or uniform pressure, and free vibration of tapered wings. The numerical results show that the proposed model is much more efficient than the conventional finite element, and their differences are within 12% in all cases of composite wing structures.

Influence of Female Age on Variation of Mate Choice Behavior in Mediterranean Fruit Fly (Diptera: Tephritidae)

In spite of the fact that studies concerning the mate choice by females have largely been based on the idea of the unanimity of the preference for certain male characteristics, variations in this behavior have been reported. Considering this aspect, we studied the influence of female age on mate choice and on the acceptance of courting by males of different ages in lab-reared medflies. The effects of the age of both sexes on the total courtship duration and on the behavioral units performed by males were also examined. Our results demonstrated that: (1) 4 to 12 day-old females prefer younger males; (2) 20 day-old females were less selective; (3) the acceptance of courting was not influenced by male age neither by the duration of behavioral units of courtship; (4) only the duration of continuous wing vibration was affected by the age of both sexes.

Ontogeny of Drosophila melanogaster female sex‐appeal and cuticular hydrocarbons

The chemical communication system in Drosophila melanogaster Meigen, 1830 plays a major role in courtship and consists of the male-specific cis-Vaccenyl acetate and sex-specific contact pheromones, cuticular hydrocarbons (CHC), which build up during ontogeny (first 4 days). They replace longer CHCs, common to both sexes and present only after the imaginal eclosion. A detailed quantitative description of the evolution of cuticular unsaturated hydrocarbons with age is presented here for males and females of different D. melanogaster strains, which have been bred in well controlled environments. Monoenes appear in both sexes at around 12 h, before female dienes. The present paper argues that this is likely linked to the switching on of a new set of genes. Ecdysone, which is more abundant in females than in males during this critical period, might control this switch. Parallel behavioral studies show that whereas female of all ages trigger early mature male courtship steps like wing vibration, only females older than 1 day trigger late courtship steps like attempted copulation. This supports the hypothesis that late male courtship steps might be triggered by the CHCs, which build up after this age, especially female-specific (Z,Z)-7,11 - and (Z,Z)-5,9-dienes.

A two-step mechanism controls the timing of behaviour leading to emergence from soil in adult males of the scarab beetle Dasylepida ishigakiensis

Adults of the white grub beetle Dasylepida ishigakiensis Niijima et Kinoshita (Coleoptera: Scarabaeidae) emerge from the soil around dusk for mating on subtropical islands. The present study examines the factors controlling the emergence of males in the laboratory. There are two steps involved. Standby behaviour (i.e. insect head appears at the soil surface) can be observed for several hours before the beetles actually emerge for mating. The standby behaviour is facilitated by warm conditions, although the proportion of standby individuals is influenced not only by the temperature on that day, but also by that on the previous day. Experiments in which beetles are exposed to photoperiod and thermoperiod combinations, in and out of phase, show that temperature is more important in inducing standby and emerging behaviour than light alone. For the second step, factors such as temperature, light and the presence of the female sex pheromone determine whether males will leave the standby position and emerge onto the ground. The female sex pheromone stimulates standby beetles to exhibit emerging and wing vibration behaviours, although the effect depends on when it is presented to beetles. Beetles burrow back into the soil; this behaviour is influenced by illumination and time of the day but not by temperature. The results suggest that D. ishigakiensis possesses a sophisticated mechanism controlling male emergence from the soil.

Overexpression of a repressor isoform of CrebB-17A lengthens courtship break in the fruit fly Drosophila melanogaster (Diptera: Drosophilidae)

The Courtship of Drosophila Melanogaster males involves a sequence of characteristic behavioral elements. Identification of the genes required for active male courtship will help our understanding of the molecular mechanisms for maintaining male courtship activity. In this study, we examined the effect of conditional suppression of the activity of Drosophila transcription factor CrebB-17A on each courtship element by analyzing courtship using an event recorder. The mean frequencies of orientation, following, and wing vibration decreased in males overexpressing the CrebB-17A repressor. The mean durations of the courtship bout and each courtship element were normal in these flies and that of courtship break was markedly lengthened. These findings show that ongoing CrebB-17A activity is required for maintaining courtship break at the wild-type level, suggesting that CrebB-17A-mediated gene expression is involved in the reinitiation of male courtship after courtship break in Drosophila.

The Shaping of Male Courtship Posture by Lateralized Gustatory Inputs to Male-Specific Interneurons

Unilateral wing vibration to generate "love songs" is a hallmark of male courtship posture in Drosophila melanogaster. In contrast, males of some other Drosophila species extend both wings simultaneously during courtship. Thus, the patterns of wing movement vary among species and are under stringent genetic control, although there are few variations among individuals within a single species. These observations prompted the postulation that the proper wing display by courting males of D. melanogaster does not require sensory inputs. Here we show that when males of D. melanogaster are deprived of gustatory inputs mediated by the sensory neurons expressing the taste receptor gene Gr32a, a close relative to the pheromone receptor gene Gr68a, they often fail to perform unilateral wing extension during courtship because they become unable to keep a wing in the resting position while extending another wing. The tarsal amputation of a foreleg, but not other legs, increased the occurrence of simultaneous wing extension, indicating that Gr32a-expressing cells in this structure are involved in the regulation of courting posture. A similar simultaneous wing extension was also observed in males in which the putative pheromone-binding protein gene Obp57d was inactivated. The axons of Gr32a-expressing cells project to the subesophageal ganglion, where their terminals unilaterally contact mAL, which are male-specific fruitless (fru)-expressing interneurons that have bilateral branches. Our observations strongly suggest that gustatory pheromone inputs ensure the correct laterality of wing vibration that conforms to the species-specific behavioral pattern.

A technique for predicting strength properties of an aircraft wing

A technique for evaluating and predicting flexural stiffness of an aircraft wing in the process of operation based on measuring the first tone of flexural wing vibrations in flight is proposed.

Acoustic courtship songs in males of the fruit fly Anastrepha ludens (Diptera: Tephritidae) associated with geography, mass rearing and courtship success

The Sterile insect Technique (SiT) has been used successfully to control or eradicate fruit flies. The commonly observed inferiority of mass-reared males, compared with wild males, when they are paired with wild females, is apparently due to their inadequate courtship. Anastrepha ludens males produce two types of wing vibration during courtship and mating, the sound and the or precopulatory sound. There were clear differences in the calling songs between successful and unsuccessful courtships in sterile (irradiated) and fertile Mexican flies. Among sterile flies, successful males produce longer buzzes, shorter interpulses and a higher power spectrum in the signal. Fertile flies showed the same trend. For mating songs a significant dif- ference occurred in two parameters: power spectrum between sterile and fertile flies with respect to the type of song, and the signal duration and intensity were greater in non-irradiated flies. Calling songs of wild flies compared with laboratory grown flies from Mexico had shorter interpulses, longer pulses, and a greater power spectrum. However, in the case of premating songs, the only difference was in the intensity, which was sig- nificantly greater in wild males. An unexpected result was not observing pulses during pheromone deposition in wild males from Costa Rica. Comparing the premating songs of wild flies from Costa Rica and Mexico, no significant differences were observed in the duration, and the intensity of the signal was slightly greater in flies from Mexico. Rev. Biol. Trop. 57 (Suppl. 1): 257-265. Epub 2009 November 30.

A homeotic mutation influences the wing vibration patterns during mating in males of the silkworm moth Bombyx mori

An abnormality in the wing vibration pattern in males of the E Nc homeotic mutant of Bombyx mori was investigated. The wild-type (+/+) males show a switching of the rhythmic wing vibrations from a sequential pattern to an intermittent pattern during mating, whereas the E Nc mutants show a sequential pattern both before and during mating. Wing motions in +/+ males became small during mating, but those in +/ E Nc males did not. Ablation of the head ganglia of +/+ and +/ E Nc males during mating caused no change in the motor patterns of wing vibrations. Ablation or cooling of the posterior abdomen in the +/+ males during mating caused sequential wing vibrations, suggesting that the change in wing vibrations is induced by signals from the posterior abdomen. The pterothoracic ganglion in the +/ E Nc males is separated into two ganglia, in contrast to the complete ganglionic fusion in the +/+ males. The neurons in the pterothoracic ganglion stained from abdominal nerve cords are homologus in +/+ and +/ E Nc males, but many of these in +/ E Nc males are elongated along the anteroposterior axis. These results suggest that the wing vibration pattern is restricted by genetic factors through reconstruction of the thoracic nervous system during metamorphosis.

Vibration and Flutter Characteristics of a Folding Wing

Studies are presented that characterize the dynamic aeroelastic aspects of a morphing aircraft design concept. The notion of interest is a folding wing design resulting in large-scale wing area changes. A finite element approach is used to investigate the sensitivity of natural frequencies and flutter instabilities to the wing position (e.g., fold angle), actuator stiffness, and vehicle weight. Sensitivities in these areas drive design requirements and raise flight envelope awareness issues. The study is presented in two parts as a comparison between two models of varying complexity. A simple folding wing model, based on the Goland wing, is analyzed and results are compared with a built-up structural model of the proposed full scale morphing vehicle.