1153 INTRODUCTION Odours and pheromones are omnipresent as signals and cues and are important carriers of information in arthropods. In social insects in particular, communication critically depends on chemical signalling, with the need for efficiency growing with the degree of sociality. The highest degree of sociality in insects, as well as in any other animal, is found in species where the members of one colony together represent a highly eusocially organized superorganism (Wilson and Sober, 1989; Seeley, 1989; Wilson and Hölldobler, 2005; Reeve and Hölldobler, 2007; Gardner and Grafen, 2009). The most well known examples of superorganisms are ants, honey bees and termites. Thanks to their study we now know that an efficient communication between colony members using pheromones and other semiochemicals is indeed an essential basis for the maintenance of a superorganism. Often, the use of pheromones to recruit nestmates for collecting food or for defence is taken to illustrate the relevance of pheromones for the coordination of colony activities (Vander Meer, 1998; Wyatt, 2003). While a lot is already known about chemical communication in ants and honey bees, our knowledge is far behind and partly controversial in case of the Meliponini, the so-called stingless bees, a less well known taxonomic group of superorganismic arthropods (Camargo and Pedro, 1992; Michener, 2000). This is surprising because the meliponines are very important pollinators in tropical rain forests and also valued study objects for those seeking broad insights into tropical ecology (Roubik, 1989). In this paper we will dissect current controversy concerning the Meliponini which refers to the communicative role of their mandibular gland secretions. The mandibular glands were the first glands proposed to play an important role in meliponine communication (Lindauer and Kerr, 1958). Likewise they were reported to be important in the communication of a great number of other Hymenoptera, although sufficiently detailed studies are available for very few species. The many species of meliponines (>400 circumtropical species) differ vastly in foraging habits and defensive ‘strategies’ and bees of the same or different sympatric species frequently compete for resources (Schwarz, 1932; Johnson and Hubbell, 1974; Roubik, 1989; Nagamitsu and Inoue, 1997; Eltz et al., 2002; Slaa, 2003; Slaa, 2006). Therefore they are particularly suited for flower ecology studies and for the study of defensive and aggressive behaviour. The behavioural differences between them have so far been mainly attributed to differences in body and/or colony size and nesting behaviour (Michener, 1974; Camargo and Pedro, 1992; Roubik, 2006). Accordingly, one finds (i) intranidal and intrasuperorganismic, (ii) internidal and intersuperorganismic, and (iii) interspecific conflicts. Analogous to the situation in ants, cleptoparasitic species (‘robber bees’) add to the diversity of meliponine bee behaviour. In all these behaviours, efficient communication between colony members will enhance the effect of defence and aggression as well The Journal of Experimental Biology 212, 1153-1162 Published by The Company of Biologists 2009 doi:10.1242/jeb.021113 Mandibular gland secretions of meliponine worker bees: further evidence for their role in interspecific and intraspecific defence and aggression and against their role in food source signalling Dirk Louis P. Schorkopf 1, *, Michael Hrncir 1,2 , Sidnei Mateus 2 , Ronaldo Zucchi 2 , Veronika M. Schmidt 1 and Friedrich G. Barth 1 1 Department of Neurobiology and Cognition Research, Center for Organismal Systems Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria and 2 Department of Biology, FFCLRP, University of São Paulo, Avenida Bandeirantes 3900, 14040-901 Ribeirão Preto, SP, Brazil *Author for correspondence (e-mail: sylvilagusbrasiliensis@gmx.at) Accepted 3 February 2009 SUMMARY Like ants and termites some species of stingless bees (Meliponini), which are very important pollinators in the tropics, use pheromone trails to communicate the location of a food source. We present data on the communicative role of mandibular gland secretions of Meliponini that resolve a recent controversy about their importance in the laying of such trails. Volatile constituents of the mandibular glands have been erroneously thought both to elicit aggressive/defensive behaviour and to signal food source location. We studied Trigona spinipes and Scaptotrigona aff. depilis (‘postica’), two sympatric species to which this hypothesis was applied. Using extracts of carefully dissected glands instead of crude cephalic extracts we analysed the substances contained in the mandibular glands of worker bees. Major components of the extracts were 2-heptanol (both species), nonanal (T. spinipes), benzaldehyde and 2-tridecanone (S. aff. depilis). The effect of mandibular gland extracts and of individual components thereof on the behaviour of worker bees near their nest and at highly profitable food sources was consistent. Independent of the amount of mandibular gland extract applied, the bees overwhelmingly reacted with defensive behaviour and were never attracted to feeders scented with mandibular gland extract or any of the synthetic chemicals tested. Both bee species are capable of using mandibular gland secretions for intra- and interspecific communication of defence and aggression and share 2-heptanol as a major pheromone compound. While confirming the role of the mandibular glands in nest defence, our experiments provide strong evidence against their role in food source signalling. Key words: eusocial bees, communication, agonistic behaviour, semiochemicals, trail substance. THE฀JOURNAL฀OF฀EXPERIMENTAL฀BIOLOGY