Recruitment communication in stingless bees

Research project P 14328 Recruitment Communication in Stingless Bees Friedrich G. BARTH 08.05.2000 In eusocial insects living in colonies with many individuals the economy of the exploitation of food sources is of prime importance. Accordingly, highly sophisticated communication systems have devoloped. The most well known of these is the dance language of the honeybee. However, even in this case important questions related to the relevant communication channels are still under debate. The subject of the present project are the highly social stingless bees (Meliponinae), a group of more than 20.000 species with a remarkable diversity of recruitment and communication mechanisms. These are of interest not only with regard to possible prototypes of the honeybee dance language but also deserve attention in their own right There are valuable first glimpses at the recruitment and communication behavior of stingless bees but only a few species were studied in some detail and none extensively enough. Our own contribution shall concentrate on the signaling and sensory mechanisms involved in stingless bee recruitment communication. Up to date technology shall be applied to a selected number of neotropical species to diligently sort out various signals and their functions in recruitment behavior Taking an organismic approach specialized work in the laboratory shall be integrated with field work and behavioral studies. The main aims of the project are the following 1. To find out reasons for the diversity of the recruitment behavior in stingless bees. In several species we will try to see whether differences in behavior and in the repertoire of signals (used for communication with prospective recruits) are related to colony size and/or food availability. Also, some of the obvious behavioral patterns and signals shall be analysed quantitatively for the first time. 2. Analysis of recruitment behavior and associated mechanical signals in the nest proper which was never done before in any species of stingless bees. We will use a miniature infrared video-camera to closely observe the bees and a portable laser-vibrometer system to analyze vibratory signals and their transmission through the various components of the nest. 3. Quantitative description and analysis of scent marking behavior (outside the nest, in species laying a scent trail for the guidance of newcomers to the food source) and its significance, chemical analysis of the scent marks, and behavioral and simple electrophysiological experiment to establish the relevance of scent components. A significant part of the project Will be carried out in Brazil in collaboration with Professor R. Zucchi (University of Sao Paulo, Ribeirao Preto). Work related to the chemical analysis of scent marks will be done with Dr. M. Ayasse (University of Vienna) and Professor W. Francke (University of Hamburg), two experienced specialists in this field of research.

Stingless bees (Meliponini) form a group of about 500 species of tropical and subtropical bees. As highly social insects they use various ways to effectively exploit food sources . Foragers inform their nestmates about resources and make them join in their efforts to collect food for the colony ("recruitment"). Project P14328 dealt with "recruitment communication" in stingless bees. All experiments with live bees were carried out in collaboration with Professor Ronaldo Zucchi of the University of São Paulo, Brazil. The search for food and associated communication behaviors follow one of two patterns: Whereas in the "Melipona group" foragers communicate and recruit inside the nest, species of the "Trigona group" lay scent trails outside the nest to guide recruits to the food. Thus our research concentrated on communication (i) inside and (ii) outside the bees` nest. (i) The most intriguing question is whether stingless bees like Melipona have symbolic communication similar to the dance language of the honeybee to indicate the location of the food source. According to our findings this is not the case. Despite claims of the contrary in the literature we still do not know how food source location is communicated by Melipona and allies. We particularly addressed the vibratory signals (also given off as airborne sound) emitted by foragers during the unloading of their food in the nest to other bees. According to our previous studies neither their temporal nor spectral structure correlates with food location. It now turned out that they significantly vary with sugar concentration (caloric gain); "liveliness" of the vibrations depends on food quality. Another important finding is the ability of the foragers to use optic image flow to estimate flight distance. As seen in most recent experiments, however, visual flow intensity is not used to code distance by the vibratory signals. Chemical marking of the food source by the foragers helps recruits to find it. Surprisingly, the source of these pheromones is a newly described tendon gland in the leg but not the tarsal gland as so far suggested for other bees. (ii) Communication in the Trigona group is even less well studied than in Melipona. Very little is known about the scent trails. Our discoveries are the following. Recruitment in "scent trail species" is very successful and food source localization very precise. Recruitment success does not appear inferior to that of honeybees. Apart from scent path pheromones different scent marks are used to tag the food source. For scent trail marking the bees do not use their mandibular glands as so far assumed but their labial glands.