Dirk Louis P. Schorkopf

Spitting out information: Trigona bees deposit saliva to signal resource locations

Stingless bees of the species Trigona spinipes (Fabricius 1793) use their saliva to lay scent trails communicating the location of profitable food sources. Extracts of the cephalic labial glands of the salivary system (not the mandibular glands, however) contain a large amount (approx. 74%) of octyl octanoate. This ester is also found on the scent-marked substrates at the feeding site. We demonstrate octyl octanoate to be a single compound pheromone which induces full trail following behaviour. The identification of the trail pheromone in this widely distributed bee makes it an ideal organism for studying the mechanism of trail following in a day flying insect.

The sound field generated by tethered stingless bees (Meliponascutellaris): inferences on its potential as a recruitment mechanisminside the hive

SUMMARY 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 transfering 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 bees 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 ⩽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 Johnstons organ of the bee antenna. Taking the physiological properties of the honey bees Johnstons 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.

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

SUMMARY 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.

Food profitability affects intranidal recruitment behaviour in the stingless bee Nannotrigona testaceicornis

Does the food’s sugar concentration affect recruitment behaviour in the stingless bee Nannotrigona testaceicornis? We recorded intranidal forager behaviour while offering sugar water of constant, increasing, or decreasing concentrations. Running speed was not correlated with sugar concentration but the jostling contacts/sec were. Food profitability also affected the recruiter’s thorax vibrations: Pulse duration and duty cycle followed both concentration increases and decreases. Sugar concentration also influenced the number of recruited bees. In comparison to the phylogenetically closely related Scaptotrigona, Nannotrigona’s intranidal recruitment behaviour showed a more elaborate association with food profitability. This is likely to reflect differences in ecology and foraging strategies as Nannotrigona — in contrast to Scaptotrigona — does not lay scent trails to guide recruits to a food source.ZusammenfassungIn der vorliegenden Studie wurde das Rekrutierungsverhalten der stachellosen Biene Nannotrigona testaceicornis untersucht. Phylogenetisch ist diese Art nahe mit der Gattung Scaptotrigona verwandt, jedoch unterscheidet sie sich im Verhalten während der Futtersuche: Nannotrigona legt im Gegensatz zu Scaptotrigona keine Duftpfade als Wegweiser zur Futterquelle. Obgleich mit Nannotrigona nicht nahe verwandt, legen auch Bienen der Gattung Melipona keinen Duftpfad bei der Nahrungssuche an. Frühere Arbeiten (z.B. Nieh et al., 2003; Hrncir et al., 2004a,b; Schmidt et al., 2006b) beschrieben das Rekrutierungsverhalten von Melipona und Scaptotrigona innerhalb des Nestes. Dabei zeigte sich, dass Melipona (kein Duftpfad) auf Veränderungen von Futterqualität mit einer Veränderung des Verhaltens (Thoraxvibrationen) innerhalb des Nestes reagiert, während Scaptotrigona (Duftpfad) nach Veränderungen der Futterqualität im Nest ihr Verhalten kaum änderte. Die vorliegende Studie fragt nach dem Einfluss der Futterqualität auf das intranidale Rekrutierungsverhalten einer Art, die trotz naher taxonomischer Verwandtschaft mit Duftpfad-Bienen keinen Duftpfad auslegt. Im Experiment wurde Nannotrigona 35 m vom Nest entfernt eine Futterquelle geboten, deren Zuckerwasserkonzentration konstant gehalten (Kontrollversuche) oder erhöht bzw. erniedrigt wurde. Zugleich wurde innerhalb des Nestes gemessen, mit welcher Geschwindigkeit die Sammelbienen im Nest laufen, wie oft sie ihre Nestgenossinnen pro Sekunde rempeln und welche Thoraxvibrationen sie abgeben. Die Kontrollversuche zeigten, dass die Rempelaktivität gegensätzlich zur Laufgeschwindigkeit bei konstanter Zuckerkonzentration über die Versuchszeit konstant blieb. Mit veränderten Zuckerkonzentrationen änderten die Bienen ihre Rempelaktivität: Während deren Intensität mit zunehmendem Zuckergehalt ebenfalls zunahm, verminderte sie sich infolge abnehmender Zuckerkonzentration. Ebenso hingen die Eigenschaften der Thoraxvibrationen stark von der Konzentration des Futterwassers ab: Bei ansteigender Zuckerkonzentration erhöhten die Bienen die Pulslänge der Vibrationen und auch der Duty Cycle (Aktivitätsmaß) stieg signifikant an. Bei stündlich abnehmender Zuckerkonzentration wurden die Vibrationspulse signifikant kürzer, die Pausen zwischen den Pulsen länger und damit auch der Duty Cycle kleiner. Diese Befunde erfüllen die Erwartungen, dass Bienen ohne Duftpfad (Nannotrigona) eine raffiniertere Kommunikation innerhalb des Nestes anwenden als nahe verwandte Bienen, die Duftpfade außerhalb des Nestes als Wegweiser nutzen.

Pheromone paths attached to the substrate in meliponine bees: helpful but not obligatory for recruitment success.

In contrast to marking of the location of resources or sexual partners using single-spot pheromone sources, pheromone paths attached to the substrate and assisting orientation are rarely found among flying organisms. However, they do exist in meliponine bees (Apidae, Apinae, Meliponini), commonly known as stingless bees, which represent a group of important pollinators in tropical forests. Worker bees of several Neotropical meliponine species, especially in the genus Scaptotrigona Moure 1942, deposit pheromone paths on substrates between highly profitable resources and their nest. In contrast to past results and claims, we find that these pheromone paths are not an indispensable condition for successful recruitment but rather a means to increase the success of recruiters in persuading their nestmates to forage food at a particular location. Our results are relevant to a speciation theory in scent path-laying meliponine bees, such as Scaptotrigona. In addition, the finding that pheromone path-laying bees are able to recruit to food locations even across barriers such as large bodies of water affects tropical pollination ecology and theories on the evolution of resource communication in insect societies with a flying worker caste.

Combining Attractants and Larvicides in Biodegradable Matrices for Sustainable Mosquito Vector Control

Background There is a global need for cost-effective and environmentally friendly tools for control of mosquitoes and mosquito-borne diseases. One potential way to achieve this is to combine already available tools to gain synergistic effects to reduce vector mosquito populations. Another possible way to improve mosquito control is to extend the active period of a given control agent, enabling less frequent applications and consequently, more efficient and longer lasting vector population suppression. Methodology/principal findings We investigated the potential of biodegradable wax emulsions to improve the performance of semiochemical attractants for gravid female culicine vectors of disease, as well as to achieve more effective control of their aquatic larval offspring. As an attractant for gravid females, we selected acetoxy hexadecanolide (AHD), the Culex oviposition pheromone. As toxicant for mosquito larvae, we chose the biological larvicides Bacillus thuringiensis israelensis (Bti) and Bacillus sphaericus (Bs). These attractant and larvicidal agents were incorporated, separately and in combination, into a biodegradable wax emulsion, a commercially available product called SPLAT (Specialized Pheromone & Lure Application Technology) and SPLATbac, which contains 8.33% Bti and 8.33% Bs. Wax emulsions were applied to water surfaces as buoyant pellets of 20 mg each. Dose-mortality analyses of Culex quinquefasciatus Say larvae demonstrated that a single 20 mg pellet of a 10−1 dilution of SPLATbac in a larval tray containing 1 L of water caused 100% mortality of neonate (1st instar) larvae for at least five weeks after application. Mortality of 3rd instar larvae remained equally high with SPLATbac dilutions down to 10−2 for over two weeks post application. Subsequently, AHD was added to SPLAT (emulsion only, without Bs or Bti) to attract gravid females (SPLATahd), or together with biological larvicides to attract ovipositing females and kill emerging larvae (SPLATbacAHD, 10−1 dilution) in both laboratory and semi-field settings. The formulations containing AHD, irrespective of presence of larvicides, were strongly preferred as an oviposition substrate by gravid female mosquitoes over controls for more than two weeks post application. Experiments conducted under semi-field settings (large screened greenhouse, emulating field conditions) confirmed the results obtained in the laboratory. The combination of attractant and larvicidal agents in a single formulation resulted in a substantial increase in larval mosquito mortality when compared to formulations containing the larvicide agents alone. Conclusions/significance Collectively, our data demonstrate the potential for the effective use of wax emulsions as slow release matrices for mosquito attractants and control agents. The results indicate that the combination of an oviposition attractant with larvicides could synergize the control of mosquito disease vectors, specifically Cx. quinquefasciatus, a nuisance pest and circumtropical vector of lymphatic filariasis and encephalitis.

Enantioselective Preference and High Antennal Sensitivity for (−)-Ipsdienol in Scent-Collecting Male Orchid Bees, Euglossa cyanura

Male neotropical orchid bees (Euglossini) collect volatile chemicals from their environment, store them in tibial pouches, and later expose their “perfumes” during a courtship display. Here, we showed that enantiomeric selectivity plays an important role in the choice of volatiles by male Euglossa cyanura in southern Mexico, and that behavioral selectivity is linked to antennal sensitivity. In field bioassays with equal concentrations of (+)-ipsdienol, (−)-ipsdienol, and racemate, males preferred the (−)-isomer to the racemate, while neglecting the (+)-isomer. Correspondingly, antennae of male E. cyanura showed larger electroantennographic responses to the (−)-isomer than to the (+)-isomer. In comparison, antennae of male Euglossa mixta, which are not attracted to any form of ipsdienol, showed lower electroantennographic responses to (−)-ipsdienol than did antennae of E. cyanura, and also did not differ in sensitivity with respect to the (+)- or (−)-isomers. We suggest that (−)-ipsdienol is an important component of perfume signals in male E. cyanura, which have undergone selection in favor of increased antennal sensitivity to that enantiomer.

Nectar profitability, not empty honey stores, stimulate recruitment and foraging in Melipona scutellaris (Apidae, Meliponini)

In stingless bees (Meliponini) like in many other eusocial insect colonies food hoarding plays an important role in colony survival. However, very little is known on how Meliponini, a taxon restricted to tropical and subtropical regions, respond to different store conditions. We studied the impact of honey removal on nectar foraging activity and recruitment behaviour in Melipona scutellaris and compared our results with studies of the honey bee Apis mellifera. As expected, foraging activity increased significantly during abundance of artificial nectar and when increasing its profitability. Foraging activity on colony level could thereby frequently increase by an order of magnitude. Intriguingly, however, poor honey store conditions did not induce increased nectar foraging or recruitment activity. We discuss possible reasons explaining why increasing recruitment and foraging activity are not used by meliponines to compensate for poor food conditions in the nest. Among these are meliponine specific adaptations to climatic and environmental conditions, as well as physiology and brood rearing, such as mass provisioning of the brood.

Male meliponine bees (Scaptotrigona aff. depilis) produce alarm pheromones to which workers respond with fight and males with flight

In highly social hymenopteran societies, males mainly serve reproductive purposes. Semiochemicals enable the different hymenopteran sexes and castes to communicate with each other and to coordinate important functions within colonies. I hereby show that sexual dimorphism in meliponine bees incorporates the alarm and defence communication system. I chemically analysed the mandibular glands of Scaptotrigona aff. depilis using GCMS methods and conducted behavioural experiments in both males and female workers using cephalic and mandibular gland extracts. In addition, behaviour studies with male cephalic extracts were also conducted in Scaptotrigona bipunctata and Partamona cupira. Males and female worker bees showed differences in the content of the mandibular glands, which are responsible for alarm communication in meliponines. Males never attacked but usually fled when confronted with the mandibular gland extract content of other conspecific males or females. Interestingly, however, meliponine males were still able to raise alarm and to induce substantial amounts of aggression at nest entrances, which is different from the much better known and studied honey bees. Potential reasons are briefly discussed.