SUMMARYBees 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 nonflight 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.

SUMMARYThe honey beeʼs 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 dancerʼs thoracic vibrations in relation to changes in food profitability suggests their role as an indicator of the recruiterʼs 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.

The pheromones used by several species of stingless bees for scent trail communication are generally assumed to be produced by the mandibular glands. Here we present strong evidence that in Trigona recursa these pheromones originate from the labial glands, which are well developed in the heads of foragers. Analysis of the behavior involved in scent marking shows that a bee extends her proboscis and rubs it over the substrate. A single scent marking event lasts for 0.59+/-0.21 s while the bee runs a stretch of 1.04+/-0.37 cm on a leaf. According to choice experiments the bees are attracted by a feeder baited with labial gland extract (84.2+/-6% of the bees choose this feeder) but repelled from a feeder baited with mandibular gland extract (only 27.5+/-13.1% of the bees choose this feeder). They do not discriminate between two clean feeders (49.6+/-3% of the bees at a feeder). 87+/-5.1% of bees already feeding leave the feeder after the application of mandibular gland extract whereas only 6.2+/-4.9% and 2.6+/-4% do so when labial gland extract or pure solvent was applied.

-The two stingless bee species Melipona scutellaris and M. quadrifasciata recruit nestmates to a rich foraging site. We tested this with feeders up to 140 m away from the hive. Foragers of M. scutellaris communicated direction (up to 140 m) more accurately than distance (up to 30 m) whereas those of M. quadrifasciata communicated direction only up to 30 m and distance up to 40 m. Our data indicate that in both species recruitment is divided into two temporal phases. Whereas in an initial phase alarmed nestmates search for food at random, bees leaving the hive in the following phase are obviously provided with information about its specific location. As a consequence after 35 minutes (M. scutellaris) and 85 minutes (M. quadrifasciata), respectively, significantly more newcomers arrive at the feeder than at an identical control feeder. The differences found in the recruitment success of M. scutellaris and M. quadrifasciata are discussed in regard to the different demands of their natural habitats.

-Some species of stingless bees of the genus Melipona were reported to scent mark food sources but little is known about the chemical signals involved. We studied the origin and some properties of such scent marks in M. seminigra. Results from choice experiments suggested that the bees do not scent mark the food (sugar water) itself and that abdominal droplets were excluded as the signal source. Extracts of the most distal tarsomeres, however, attracted recruits in the same way as natural scent marks. We conclude that M. seminigra scent marks a food source by leaving "footprints" secreted at the leg tips. The footprints of at least 40 visits were needed to effectively scent mark. The chemical signal has an active range of about 1 m and its effect persists for about 2 hours. In the absence of footprints no scent marking effect was seen. This finding excludes the importance of mandibular gland secretions (if at all present) for the scent marking observed.stingless bee / Melipona / scent marking / footprint substance / recruitment

We 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 recursa SMITH, T. hypogea SILVESTRI, Scaptotrigona depilis MOURE), (ii) in solitary foraging species with possible but still doubtful communication of food location inside the nest (Melipona seminigra FRIESE, M. favosa orbignyi GUÉRIN), and (iii) in species with a less precise (Nannotrigona testaceicornis LEP., Tetragona clavipes FAB.) or no communication (Frieseomelitta varia LEP.). 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.

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 pollination effectiveness of the stingless bee Melipona quadrifasciata and the honey bee Apis mellifera was tested in tomato plots. The experiment was conducted in four greenhouses as well as in an external open plot in Ribeirão Preto, SP, Brazil. The tomato plants were exposed to visits by M. quadrifasciata in one greenhouse and to A. mellifera in another; two greenhouses were maintained without bees (controls) and an open field plot was exposed to pollinators in an area where both honey bee and stingless bee colonies are abundant. We counted the number of tomatoes produced in each plot. Two hundred tomatoes from each plot were weighed, their vertical and transversal circumferences were measured, and the seeds were counted. We collected 253 Chrysomelidae, 17 Halictidae, one Paratrigona sp, and one honey bee from the flowers of the tomato plants in the open area. The largest number of fruits (1414 tomatoes), the heaviest and largest tomatoes, and the ones with the most seed were collected from the greenhouse with stingless bees. Fruits cultivated in the greenhouse with honey bees had the same weight and size as those produced in one of the control greenhouses. The stingless bee, M. quadrifasciata, was significantly more ef-©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 8 (2): 751-757 (2009) S.A. Bispo dos Santos et al. ficient than honey bees in pollinating greenhouse tomatoes.