Veronika M. Schmidt

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.

Effectiveness of recruitment behavior in stingless bees (Apidae, Meliponini)

SummaryWe examined the ability of stingless bees to recruit nest mates to a food source (i) in group foraging species laying pheromone trails from the food to the nest (Trigona recursaSmith, T. hypogeaSilvestri, Scaptotrigona depilisMoure), (ii) in solitary foraging species with possible but still doubtful communication of food location inside the nest (Melipona seminigraFriese, M. favosa orbignyiGuérin), and (iii) in species with a less precise (Nannotrigona testaceicornisLep., Tetragona clavipesFab.) or no communication (Frieseomelitta variaLep.). The bees were allowed to collect food (sugar solution or liver in the necrophageous species) ad libitum and the forager number to accumulate, as it would do under normal unrestrained conditions. The median number of bees collecting differed considerably among the species (1.0–1436.5). It was highest in the species employing scent trails. The time course of recruitment was characteristic for most of the species and largely independent of the number of foragers involved. The two Melipona species recruited other bees significantly faster than T. recursa, S. depilis, and N. testaceicornis during the first 10 to 30 minutes of an experiment. In species laying a scent trail to guide nestmates to a food source the first recruits appeared with a delay of several minutes followed by a quick increase in forager number. The median time required to recruit all foragers available differed among the species between 95.0 and 240.0 min. These differences can at least partly be explained by differences in the recruitment mechanisms and do not simply follow from differences in colony biomass.

A stingless bee marks the feeding site in addition to the scent path (Scaptotrigona aff. depilis)

Scaptotrigona depilis uses a scent trail to guide newly recruited bees to a food source. (i) Behavioral experiments show an additional chemical marking at the food source. The bees had to choose between an unused feeder and a feeder, at which their nestmates had fed. 71 to 86% of the bees chose the used feeder where the foragers had left attractants. The used feeder also attracted bees when it was moved away from its original site to a new site halfway along the scent path or 20 m beyond it. (ii) The localization of a food source by S. depilis is very precise with regard to both direction and distance. When control feeders were 1.7 m, 8.5 m, and 17 m away from the experimental feeder (at 50 m from the nest) 97.5-100% of the recruits chose the experimental feeder where the foragers were feeding. When positioned beyond the used feeder the control feeder remained unvisited. We conclude, that markings left at the used feeder represent particular end point tags and differ from scent path markings. stingless bee / Scaptotrigona / scent marking / recruitment

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.

DESCRIPTION OF THE NEST, EGGS, AND BREEDING BEHAVIOR OF THE ENDANGERED PALE-HEADED BRUSH-FINCH (ATLAPETES PALLIDICEPS) IN ECUADOR

Abstract The Pale-headed Brush-Finch (Atlapetes pallidiceps) is a critically endangered endemic bird species that is restricted to a single valley in southern Ecuador. We present the first description of the nest, eggs, breeding behavior, and juvenal plumage of this species. Seventy-two percent of nests (n = 18) were placed on thin overhanging branches 1–3 m above the ground, directly beneath the top layer of foliage in dense thickets. Nesting material consisted of various proportions of grass, twigs, and bamboo stalks and leaves. Clutch sizes ranged from 1–3 eggs (n = 22), and ≥55% of nests (n = 18) were parasitized by Shiny Cowbirds (Molothrus bonariensis). The background color of eggs was buffish white to bluish, and they were spotted and blotched with diffuse brown markings. Mean egg size was 24 × 17.8 mm. Fledgling plumage differed from adult plumage and had some characteristics similar to the adult White-winged Brush-Finch (Atlapetes leucopterus). Females alone incubated the eggs, and both parents fed the offspring. Incubation and nestling times were 12–14 days each. Fledglings of the Pale-headed Brush-Finch were led for several weeks after fledging. No pair initiated a second clutch after a successful first one (n = 16), but we observed second and third clutches after nest failure had occurred. Prolonged postfledging care is assumed to prevent multiple broods of the Pale-headed Brush- Finch during one season.

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.