Thoracic Vibrations Research Articles

Buzz-pollinating bees deliver thoracic vibrations to flowers through periodic biting

Pollinator behavior is vital to plant-pollinator interactions, affecting the acquisition of floral rewards, patterns of pollen transfer, and plant reproductive success. During buzz pollination, bees produce vibrations with their indirect flight muscles to extract pollen from tube-like flowers. Vibrations can be transmitted to the flower via the mandibles, abdomen, legs, or thorax directly. Vibration amplitude at the flower determines the rate of pollen release and should vary with the coupling of bee and flower. This coupling often occurs through anther biting, but no studies have quantified how biting affects flower vibration. Here, we used high-speed filmography to investigate how flower vibration amplitude changes during biting in Bombus terrestris visiting two species of buzz-pollinated flowering plants: Solanum dulcamara and Solanum rostratum (Solanaceae). We found that floral buzzing drives head vibrations up to 3 times greater than those of the thorax, which doubles the vibration amplitude of the anther during biting compared with indirect vibration transmission when not biting. However, the efficiency of this vibration transmission depends on the angle at which the bee bites the anther. Variation in transmission mechanisms, combined with the diversity of vibrations across bee species, yields a rich assortment of potential strategies that bees could employ to access rewards from buzz-pollinated flowers.

Biomechanical properties of non-flight vibrations produced by bees.

Bees use thoracic vibrations produced by their indirect flight muscles for powering wingbeats in flight, but also during mating, pollination, defence and nest building. Previous work on non-flight vibrations has mostly focused on acoustic (airborne vibrations) and spectral properties (frequency domain). However, mechanical properties such as the vibration's acceleration amplitude are important in some behaviours, e.g. during buzz pollination, where higher amplitude vibrations remove more pollen from flowers. Bee vibrations have been studied in only a handful of species and we know very little about how they vary among species. In this study, we conducted the largest survey to date of the biomechanical properties of non-flight bee buzzes. We focused on defence buzzes as they can be induced experimentally and provide a common currency to compare among taxa. We analysed 15,000 buzzes produced by 306 individuals in 65 species and six families from Mexico, Scotland and Australia. We found a strong association between body size and the acceleration amplitude of bee buzzes. Comparison of genera that buzz-pollinate and those that do not suggests that buzz-pollinating bees produce vibrations with higher acceleration amplitude. We found no relationship between bee size and the fundamental frequency of defence buzzes. Although our results suggest that body size is a major determinant of the amplitude of non-flight vibrations, we also observed considerable variation in vibration properties among bees of equivalent size and even within individuals. Both morphology and behaviour thus affect the biomechanical properties of non-flight buzzes.

Airborne ultrasound for the contactless mapping of surface thoracic vibrations during human vocalizations: A pilot study

Physical examination of the thorax is key to the clinical diagnosis of respiratory diseases. Among other examination techniques, palpation evaluates the transmission of high-frequency vibrations produced by vocalizations (tactile fremitus), which helps the physicians to identify abnormalities within the respiratory system. We propose the use of an airborne ultrasound surface motion camera (AUSMC) to quantitatively map the vibrations induced by subject vocalization. This approach could make the examination of vocal fremitus quantifiable, reproducible, and archivable. Massive data collection of vocal fremitus could allow using artificial intelligence algorithms to isolate vibration patterns that could help disease identification. Until now, in contrast, the interpretation of vocal fremitus has been subject to the physician’s experience and remains subjective. In the present work, we demonstrate the capabilities of the AUSMC to measure vocal fremitus thoracic vibration maps on 77 healthy volunteers. We have observed a spatial dependence of vibration maps on vocalization frequency. We observed that the left lung generates fewer surface vibrations than the right one, which was expected according to their respective dimensions. We also discuss the implications of our findings.

Recruitment Behaviour in an African Meliponine Bee Species (hymenoptera, Apidae: Meliponini): Understanding Glandular Origin and Pheromonal Components

Meliponine bees are speculated to use a variety of communication mechanisms to effectively recruit workers of a colony to collect sufficient amounts of food to nourish the entire nest population. Mechanisms used to convey such information include thoracic vibrations and trophallaxis within the nest; footprint secretions and pheromone marks deposited in the field, or a combination of these signals and cues. There have been numerous discrepancies about the origin of trail pheromone production from the head, thorax, abdomen and leg regions of meliponine bees. Because the glandular origin of pheromone marks deposited by African meliponine bee’s species has not yet been investigated, we first confirmed if these species actually carry out scent marking and recruitment behaviour at visited food sources. Secondly, we tested if either nasonov or tarsal gland secretions elicited trail-following behaviour in newly recruited bees by means of chemical and electro-physiological analyses as well as with bio-assays testing both natural extracts and synthetic pheromone compounds from both glands. Significant differences were observed in the foraging patterns of the four bee species on collected resources (nectar, pollen and water) as the synthetic compound, (E)-β-farnesene was significantly as attractive to foragers of the four species when compared to the natural nasonov gland extract. Our results showed a significantly higher proportion of foragers from the four species been attracted to food resources baited with natural extracts from their own glands and recruited additional foragers to such baited food sites.
 Keywords: Meliponine bee species, recruitment behaviour, nasonov glands, tarsal glands

How Much Pollen Do Beelike Floral Vibrations Remove from Different Types of Anthers?

Premise of research. Bees rely on pollen for growth and reproduction and have evolved a variety of behaviors to remove pollen from plants with diverse floral morphologies. Notably, some bees use vibrations generated by their thoracic muscles to remove pollen from flowers. These floral buzzes can effectively remove pollen from species with poricidal flowers (e.g., anthers that open through small apical pores). However, little is known about the effectiveness of floral buzzes in removing pollen from nonporicidal flowers. Here, we compare pollen release in species and with (Solanum rostratum, Solanum dulcamara, and Solanum lycopersicum; Solanaceae) and without (Sinapis alba and Raphanus caudatus; Brassicaceae) poricidal anthers.Methodology. We used a shaker and a laser vibrometer (for calibration) to apply controlled mechanical vibrations of different magnitudes (amplitude velocity) to flowers and used a particle counter to estimate the relative and absolute number of pollen grains removed. Pollen release under different vibration amplitude velocities was analyzed using a linear mixed effects model.Pivotal results. Floral buzzes removed, proportionally, more pollen in nonporicidal than in poricidal flowers. Yet because poricidal flowers contain significantly more pollen grains per flower, buzzing poricidal flowers result in more pollen grains removed per buzz. As expected, pollen release increased with amplitude velocity of the applied vibrations.Conclusions. Our results show that floral buzzing is an effective behavior for removing pollen from different types of floral morphologies, and we suggest that the less frequent buzzing of nonporicidal flowers may be explained by the potentially high energetic costs of producing thoracic vibrations when pollen can be gathered by less expensive means.

Low toxicity crop fungicide (fenbuconazole) impacts reproductive male quality signals leading to a reduction of mating success in a wild solitary bee

Abstract Recent reports on bee health suggest that sublethal doses of pesticides have negative effects on wild bee reproduction and ultimately on their population growth. Females of the solitary horned mason bee Osmia cornuta, evaluate thoracic vibrations and odours of males to assess male quality. When certain criteria are met, the female accepts the male and copulates. However, these signals were found to be modified by sublethal doses of pesticides in other hymenopterans. Here, we tested whether sublethal doses of a commonly used fungicide (Fenbuconazole) impact male quality signals and mating success in O. cornuta. Males exposed to fenbuconazole exhibited reduced thoracic vibrations and an altered cuticular hydrocarbon profile compared to the control bees. Moreover, males exposed to the fungicide were less successful in mating than control males. Synthesis and applications. Our results indicate that a low toxicity fungicide can negatively affect male reproductive success by altering behavioural and chemical cues. This could explain the decreasing pollinator populations in a pesticide‐polluted environment. This study highlights the need for a more comprehensive approach, including behaviour and chemical cues, when testing new pesticides and a more cautionary approach to the pesticides already used on crops.

A multi-point heart rate monitoring using a soft wearable system based on fiber optic technology

Early diagnosis can be crucial to limit both the mortality and economic burden of cardiovascular diseases. Recent developments have focused on the continuous monitoring of cardiac activity for a prompt diagnosis. Nowadays, wearable devices are gaining broad interest for a continuous monitoring of the heart rate (HR). One of the most promising methods to estimate HR is the seismocardiography (SCG) which allows to record the thoracic vibrations with high non-invasiveness in out-of-laboratory settings. Despite significant progress on SCG, the current state-of-the-art lacks both information on standardized sensor positioning and optimization of wearables design. Here, we introduce a soft wearable system (SWS), whose novel design, based on a soft polymer matrix embedding an array of fiber Bragg gratings, provides a good adhesion to the body and enables the simultaneous recording of SCG signals from multiple measuring sites. The feasibility assessment on healthy volunteers revealed that the SWS is a suitable wearable solution for HR monitoring and its performance in HR estimation is strongly influenced by sensor positioning and improved by a multi-sensor configuration. These promising characteristics open the possibility of using the SWS in monitoring patients with cardiac pathologies in clinical (e.g., during cardiac magnetic resonance procedures) and everyday life settings.

The kinocardiograph for assessment of changes in haemodynamic load in patients with chronic heart failure with reduced ejection fraction.

AimsThe kinocardiograph (KCG) is an unobtrusive device, consisting of a chest sensor, which records local thoracic vibrations produced in result of cardiac contraction and ejection of blood into the great vessels [seismocardiography (SCG)], and a lower back sensor, which records micromovements of the body in reaction to blood flowing through the vasculature [ballistocardiography (BCG)]. SCG and BCG signals are translated to the integral of cardiac kinetic energy (iK) and cardiac maximum power (Pmax), which might be promising metrics for future telemonitoring purposes in heart failure (HF). As a first step of validation, this study aimed to determine whether iK and Pmax are responsive to exercise‐induced changes in the haemodynamic load of the heart in HF patients.Methods and resultsFifteen patients with stable HF with reduced ejection fraction performed a submaximal exercise protocol. KCG and cardiac ultrasound measurements were obtained both at rest and at submaximal exercise. BCG iK over the cardiac cycle (CC) increased significantly (0.0026 ± 0.0017 to 0.0052 ± 0.0061 mJ.s.; P = 0.01) during exercise, in contrast to a non‐significant increase in SCG iK CC. BCG Pmax CC increased significantly (0.92 ± 0.89 to 2.03 ± 1.95 mJ/s; P = 0.02), in contrast to a non‐significant increase in SCG Pmax CC. When analysing the systolic phase of the CC, similar patterns were found. Cardiac output (CO) ratio (i.e. CO exercise/CO rest) showed a moderate, significant correlation with BCG Pmax CC ratio (r = +0.65; P = 0.008) and with SCG Pmax CC ratio (r = +0.54; P = 0.04).Conclusions iK and Pmax measured with the KCG, preferentially using BCG, are responsive to changes in the haemodynamic load of the heart in HF patients. The combination of the BCG and SCG sensor might be of added value to fully understand changes in haemodynamics and to discriminate between an HF patient and a healthy individual.

Transmission of bee-like vibrations in buzz-pollinated plants with different stamen architectures

In buzz-pollinated plants, bees apply thoracic vibrations to the flower, causing pollen release from anthers, often through apical pores. Bees grasp one or more anthers with their mandibles, and vibrations are transmitted to this focal anther(s), adjacent anthers, and the whole flower. Pollen release depends on anther vibration, and thus it should be affected by vibration transmission through flowers with distinct morphologies, as found among buzz-pollinated taxa. We compare vibration transmission between focal and non-focal anthers in four species with contrasting stamen architectures: Cyclamen persicum, Exacum affine, Solanum dulcamara and S. houstonii. We used a mechanical transducer to apply bee-like vibrations to focal anthers, measuring the vibration frequency and displacement amplitude at focal and non-focal anther tips simultaneously using high-speed video analysis (6000 frames per second). In flowers in which anthers are tightly arranged (C. persicum and S. dulcamara), vibrations in focal and non-focal anthers are indistinguishable in both frequency and displacement amplitude. In contrast, flowers with loosely arranged anthers (E. affine) including those with differentiated stamens (heterantherous S. houstonii), show the same frequency but higher displacement amplitude in non-focal anthers compared to focal anthers. We suggest that stamen architecture modulates vibration transmission, potentially affecting pollen release and bee behaviour.

Comparison of defence buzzes in hoverflies and buzz‐pollinating bees

AbstractBees and many flies, particularly hoverflies (Syrphidae), have evolved a diverse range of mechanisms to gather pollen from a wide variety of flowering plants. Bees and hoverflies use protein‐rich pollen as a food resource to mature reproductive organs and eggs and, in bees, to feed their larvae. A particularly striking pollen‐collecting behaviour involves the production of thoracic vibrations to dislodge pollen from flowers. Vibratile pollen collection is widespread in bees (>11 600 species) but extremely rare in flies (~1 species of hoverfly). Why the use of floral vibrations to collect pollen is so rare among flies is currently unknown. A hypothesis proposed to explain why flies do not engage in vibratile or buzz pollination is that they are unable to reach the vibration amplitude required to expel pollen from anthers. Here we document, for the first time, the mechanical properties of non‐flight thoracic vibrations produced by hoverflies and compare them to the vibrations produced by buzz‐pollinating bees under similar contexts (defence buzzes). We analysed ~4000 vibrations produced by nearly 300 individuals representing 20 species of hoverflies and 22 bee taxa, recorded using a miniature piezoelectric accelerometer. We characterised both frequency and acceleration amplitude components of non‐flight thoracic vibrations and their relationship to insect size. Our results show that, after accounting for size, buzz‐pollinating bees and hoverflies produce vibrations with similar acceleration. We show experimentally that the acceleration amplitude produced by some hoverflies is sufficient to elicit pollen release from buzz‐pollinated flowers (Solanum dulcamara and S. rostratum). Our study does not support the hypothesis that the dearth of buzz‐pollinating flies is caused by their inability to produce vibrations of sufficient amplitude. We discuss alternative hypotheses to explain why most flies do not engage in buzz pollination and suggest that the lack of buzz‐pollinating flies might be best explained through their life history.

Floral vibrations by buzz-pollinating bees achieve higher frequency, velocity and acceleration than flight and defence vibrations.

Vibrations play an important role in insect behaviour. In bees, vibrations are used in a variety of contexts including communication, as a warning signal to deter predators and during pollen foraging. However, little is known about how the biomechanical properties of bee vibrations vary across multiple behaviours within a species. In this study, we compared the properties of vibrations produced by Bombus terrestris audax (Hymenoptera: Apidae) workers in three contexts: during flight, during defensive buzzing, and in floral vibrations produced during pollen foraging on two buzz-pollinated plants (Solanum, Solanaceae). Using laser vibrometry, we were able to obtain contactless measures of both the frequency and amplitude of the thoracic vibrations of bees across the three behaviours. Despite all three types of vibrations being produced by the same power flight muscles, we found clear differences in the mechanical properties of the vibrations produced in different contexts. Both floral and defensive buzzes had higher frequency and amplitude velocity, acceleration and displacement than the vibrations produced during flight. Floral vibrations had the highest frequency, amplitude velocity and acceleration of all the behaviours studied. Vibration amplitude, and in particular acceleration, of floral vibrations has been suggested as the key property for removing pollen from buzz-pollinated anthers. By increasing frequency and amplitude velocity and acceleration of their vibrations during vibratory pollen collection, foraging bees may be able to maximise pollen removal from flowers, although their foraging decisions are likely to be influenced by the presumably high cost of producing floral vibrations.

Honey bee workers generate low-frequency vibrations that are reliable indicators of their activity level.

In social insects, the tuning of activity levels among different worker task groups, which constitutes a fundamental basis of colony organization, relies on the exchange of reliable information on the activity level of individuals. The underlying stimuli, however, have remained largely unexplored so far. In the present study, we describe low-frequency thoracic vibrations generated by honey bee workers (Apis mellifera) within the colony, whose velocity amplitudes and main frequency components significantly increased with the level of an individual's activity. The characteristics of these vibrations segregated three main activity level-groups: foragers, active hive bees, and inactive hive bees. Nectar foragers, moreover, modulated their low-frequency vibrations during trophallactic food unloading to nestmates according to the quality of the collected food. Owing to their clear association with the activity level of an individual and their potential perceptibility during direct contacts, these low-frequency thoracic vibrations are candidate stimuli for providing unambiguous local information on the motivational status of honey bee workers.

Buzz-pollination in Neotropical bees: genus-dependent frequencies and lack of optimal frequency for pollen release.

Over 50 genera of bees release pollen from flower anthers using thoracic vibrations, a phenomenon known as buzz-pollination. The efficiency of this process is directly affected by the mechanical properties of the buzzes, namely the duration, amplitude, and frequency. Nonetheless, although the effects of the former two properties are well described, the role of buzz frequency on pollen release remains unclear. Furthermore, nearly all of the existing studies describing vibrational properties of natural buzz-pollination are limited to bumblebees (Bombus) and carpenter bees (Xylocopa) constraining our current understanding of this behavior and its evolution. Therefore, we attempted to minimize this shortcoming by testing whether flower anthers exhibit optimal frequency for pollen release and whether bees tune their buzzes to match these (optimal) frequencies. If true, certain frequencies will trigger more pollen release and lighter bees will reach buzz frequencies closer to this optimum to compensate their smaller buzz amplitudes. Two strategies were used to test these hypotheses: (i) the use of (artificial) vibrational playbacks in a broad range of buzz frequencies and amplitudes to assess pollen release by tomato plants (Solanum lycopersicum L.) and (ii) the recording of natural buzzes of Neotropical bees visiting tomato plants during pollination. The playback experiment indicates that although buzz frequency does affect pollen release, no optimal frequency exists for that. In addition, the recorded results of natural buzz-pollination reveal that buzz frequencies vary with bee genera and are not correlated with body size. Therefore, neither bees nor plants are tuned to optimal pollen release frequencies. Bee frequency of buzz-pollination is a likely consequence of the insect flight machinery adapted to reach higher accelerations, while flower plant response to buzz-pollination is the likely result of its pollen granular properties.

Vibrational signals of African stingless bees

Many bee species produce thoracic vibrations in various contexts. Among the social stingless bees (Meliponini) pulsed thoracic vibrations are used to communicate with nestmates. To date all studies on stingless bee vibrational communication have been conducted in the Neotropics. We, therefore, focused on six African stingless bee species of five genera: Meliponula, Hypotrigona, Liotrigona, Dactylurina, Plebeina. We analysed the signals’ temporal patterns. Vibrational signals appear to play a role in the recruitment of stingless bees. The degree of signal variation in the studied species was much lower than the variation in the signals of Neotropical stingless bees. Furthermore, the inter-signal variation of the temporal patterns exceeded intra-signal variation. This might reveal that the bees are able to modulate the temporal patterns and the signals potential communicative value. Furthermore, foraging activity correlates with pulse production in H. gribodoi and M. bocandei, supporting the hypothesis that the vibrational signals are used in the context of foraging and recruitment.

The Role of Vibrations in Population Divergence in the Red Mason Bee, Osmia bicornis

Differences in female preference for certain male characteristics can be a driving force for population divergence and speciation [1-4]. During precopulation, females of the red mason bee, Osmia bicornis, choose suitable males based on, among other criteria, their thoracic vibrations [5]. These vibrations are thought to be a signal of a male's fitness with females choosing the strongest males that can vibrate for the longest time [5]. The precise role of such vibrational signals, however, has not been determined by bioassays, and the vibrations might also play a role in species recognition [6]. There are two main subspecies of O. bicornis in Europe distinguishable only by a single morphological trait [7] (Figure S1). We therefore developed a new bioassay allowing us to impose the vibrations of one live male onto another in order to discern possible selective mate choice by females from O. bicornis originating from different regions of Europe. Females showed strong preference for males from their own region, and male vibrations were the main signal involved in this choice. Thus, vibrational signals encode not only fitness but also information about the region of origin indicating that divergence exists between the different European O. bicornis populations, which might ultimately lead to speciation. These results provide new insights into the scope of vibrational communication in bees, a group previously considered to rely predominantly on chemical signals [8, 9]. Our newly developed method should shed further light on many exciting questions concerning vibrational communication in bees and other animal taxa.

The behaviour of <i>Bombus impatiens</i> (Apidae, Bombini) on tomato (<i>Lycopersicon esculentum</i> Mill., Solanaceae) flowers: pollination and reward perception

The foraging behaviour of pollinators can influence their efficiency in pollinating certain plant species. Improving our understanding of this behaviour can contribute to an improvement of management techniques to avoid pollination deficits. We investigated the relationship between the number of visits of bumble bees (Bombus impatiens) to tomato flowers (Lycopersicon esculentum) and two variables related to the quality of the resulting fruits (weight, number of seeds), as well as the relationship between foragers’ thoracic weights, physical characteristics of thoracic vibrations (main frequency, velocity amplitude), amount of pollen removed from flowers, and the quality-related variables. In addition, we studied the capability of foragers to assess the availability of pollen in flowers. Tomato weight and seed number did not increase with the number of bee visits, neither were they correlated with the foragers’ thorax weight. Thorax weight also did not correlate with the amount of pollen removed from the flowers nor with the physical characteristics of vibration. Vibration characteristics did not change in response to the amount of pollen available on tomato flowers. Instead, foragers adjusted the time spent visiting the flowers, spending fewer time on flowers from which some pollen had already been removed on previous visits. The quantity and the production-related variables of tomatoes are not dependent on the number of bee visits (usually one visit suffices for full pollination); bigger foragers are not more efficient in pollinating tomato flowers than smaller ones; and B. impatiens foragers are capable of evaluating the amount of pollen on a flower while foraging and during pollination.

The recruiter's excitement – features of thoracic vibrations during the honey bee's waggle dance related to food source profitability

The honey bee's waggle dance constitutes a remarkable example of an efficient code allowing social exploitation of available feeding sites. In addition to indicating the position (distance, direction) of a food patch, both the occurrence and frequency of the dances depend on the profitability of the exploited resource (sugar concentration, solution flow rate). During the waggle dance, successful foragers generate pulsed thoracic vibrations that putatively serve as a source of different kinds of information for hive bees, who cannot visually decode dances in the darkness of the hive. In the present study, we asked whether these vibrations are a reliable estimator of the excitement of the dancer when food profitability changes in terms of both sugar concentration and solution flow rate. The probability of producing thoracic vibrations as well as several features related to their intensity during the waggle phase (pulse duration, velocity amplitude, duty cycle) increased with both these profitability variables. The number of vibratory pulses, however, was independent of sugar concentration and reward rate exploited. Thus, pulse number could indeed be used by dance followers as reliable information about food source distance, as suggested in previous studies. The variability of the dancer's thoracic vibrations in relation to changes in food profitability suggests their role as an indicator of the recruiter's motivational state. Hence, the vibrations could make an important contribution to forager reactivation and, consequently, to the organisation of collective foraging processes in honey bees.

Signals and cues in the recruitment behavior of stingless bees (Meliponini)

Since the seminal work of Lindauer and Kerr (1958), many stingless bees have been known to effectively recruit nestmates to food sources. Recent research clarified properties of several signals and cues used by stingless bees when exploiting food sources. Thus, the main source of the trail pheromone in Trigona are the labial, not however the mandibular glands. In T. recursa and T. spinipes, the first stingless bee trail pheromones were identified as hexyl decanoate and octyl decanoate, respectively. The attractant footprints left by foragers at the food source are secreted by glandular epithelia of the claw retractor tendon, not however by the tarsal gland. Regarding intranidal communication, the correlation between a forager's jostling rate and recruitment success stresses the importance of agitated running and jostling. There is no evidence for a "dance" indicating food source location, however, whereas the jostling rate depends on food quality. Thoracic vibrations, another intranidal signal well known in Melipona, were analyzed using modern technology and distinguishing substrate vibrations from airborne sound. Quantitative data now permit estimates of signal and potential communication ranges. Airflow jets as described for the honeybee were not found, and thoracic vibrations do not "symbolically" encode visually measured distance in M. seminigra.

Thoracic vibrations in stingless bees (Melipona seminigra):resonances of the thorax influence vibrations associated with flight but not those associated with sound production

Bees generate thoracic vibrations with their indirect flight muscles in various behavioural contexts. The main frequency component of non-flight vibrations, during which the wings are usually folded over the abdomen, is higher than that of thoracic vibrations that drive the wing movements for flight. So far, this has been concluded from an increase in natural frequency of the oscillating system in association with the wing adduction. In the present study, we measured the thoracic oscillations in stingless bees during stationary flight and during two types of non-flight behaviour, annoyance buzzing and forager communication, using laser vibrometry. As expected, the flight vibrations met all tested assumptions for resonant oscillations: slow build-up and decay of amplitude; increased frequency following reduction of the inertial load; and decreased frequency following an increase of the mass of the oscillating system. Resonances, however, do not play a significant role in the generation of non-flight vibrations. The strong decrease in main frequency at the end of the pulses indicates that these were driven at a frequency higher than the natural frequency of the system. Despite significant differences regarding the main frequency components and their oscillation amplitudes, the mechanism of generation is apparently similar in annoyance buzzing and forager vibrations. Both types of non-flight vibration induced oscillations of the wings and the legs in a similar way. Since these body parts transform thoracic oscillations into airborne sounds and substrate vibrations, annoyance buzzing can also be used to study mechanisms of signal generation and transmission potentially relevant in forager communication under controlled conditions.

The sound field generated by tethered stingless bees (Melipona scutellaris): inferences on its potential as a recruitment mechanism inside the hive

In stingless bees, recruitment of hive bees to food sources involves thoracic vibrations by foragers during trophallaxis. The temporal pattern of these vibrations correlates with the sugar concentration of the collected food. One possible pathway for transferring such information to nestmates is through airborne sound. In the present study, we investigated the transformation of thoracic vibrations into air particle velocity, sound pressure, and jet airflows in the stingless bee Melipona scutellaris. Whereas particle velocity and sound pressure were found all around and above vibrating individuals, there was no evidence for a jet airflow as with honey bees. The largest particle velocities were measured 5 mm above the wings (16.0+/-4.8 mm s(-1)). Around a vibrating individual, we found maximum particle velocities of 8.6+/-3.0 mm s(-1) (horizontal particle velocity) in front of the bee's head and of 6.0+/-2.1 mm s(-1) (vertical particle velocity) behind its wings. Wing oscillations, which are mainly responsible for air particle movements in honey bees, significantly contributed to vertically oriented particle oscillations only close to the abdomen in M. scutellaris (distances < or =5 mm). Almost 80% of the hive bees attending trophallactic food transfers stayed within a range of 5 mm from the vibrating foragers. It remains to be shown, however, whether air particle velocity alone is strong enough to be detected by Johnston's organ of the bee antenna. Taking the physiological properties of the honey bee's Johnston's organ as the reference, M. scutellaris hive bees are able to detect the forager vibrations through particle movements at distances of up to 2 cm.