ORIGINAL PAPER M. Hrncir Æ S. Jarau Æ R. Zucchi Æ F. G. Barth Thorax vibrations of a stingless bee (Melipona seminigra). I. No influence of visual flow Received: 7 January 2004 / Revised: 1 March 2004 / Accepted: 4 March 2004 / Published online: 8 April 2004 Ó Springer-Verlag 2004 Abstract An important question in stingless bee com- munication is whether the thorax vibrations produced by foragers of the genus Melipona upon their return to the nest contain spatial information about food sources or not. As previously shown M. seminigra is able to use visual flow to estimate flight distances. The present study investigated whether foraging bees encode the visually measured distance in their thorax vibrations. Bees were trained to collect food in flight tunnels lined with a black-and-white pattern on their side walls and floor, which substantially influenced the image motion they experienced. When the bees had collected inside the tunnels the temporal pattern of their vibrations differed significantly from the pattern after collecting in a natural environment. These changes, however, were not associ- ated with the visual flow experienced inside the tunnel. Bees collecting in tunnels offering little visual flow (stripes parallel to flight direction) modified their vibrations similarly to bees collecting in tunnels with high image motion (cross stripes). A higher energy expenditure due to drastically reduced flight velocities inside the tunnel is suggested to be responsible for changes in the thorax vibrations. The bees’ vibrations would thus reflect the overall energetic budget of a for- aging trip. Keywords Communication Æ Melipona Æ Optic flow Æ Stingless bee Æ Vibration Introduction A fascinating aspect of the biology of social insects is their ability to recruit nestmates to a food source and hence to regulate the energy-intake of the colony (Seeley 1995). The communication mechanisms involved have been extensively studied in honeybees, Apis mellifera, whose wagging dance represents an intriguing example of a symbolic language (Dyer 2002). The orientation of the bees’ wagging dance and its duration are highly correlated with the direction and the distance of a food source (von Frisch 1965). As is now known foraging honeybees use the visual flow experienced on a foraging trip to estimate flight distance (Esch and Burns 1995, 1996; Srinivasan et al. 1996, 1997). They not only use this mechanism to acquire information about the dis- tance to a food source but also encode the total amount of visual flow in their dance. This has been convincingly demonstrated by Srinivasan et al. (2000). These authors trained bees to collect food inside short and narrow flight tunnels which were lined with black-and-white patterns on their side walls and floor. Hence, the bees experienced considerable retinal image motion on their foraging trips. After their return to the nest the bees performed wagging dances in which the duration of the wagging phase correlated with the total amount of visual flow but not with the absolute distance flown. In stingless bees we encounter a rich variety of recruitment mechanisms (Lindauer and Kerr 1958; Jarau et al. 2003). Most efficiently, bees of the genus Scaptotrigona guide recruits to the precise location of a food source by laying scent trails (Lindauer and Kerr 1958; Kerr et al. 1963; Schmidt et al. 2003; Jarau et al. 2003). With less success and precision bees of the genus Melipona guide their nestmates to a food source without using such scent trails (Lindauer and Kerr 1958; Nieh and Roubik 1995; Jarau et al. 2000, 2003). The mecha- nisms involved in the recruitment are still poorly understood in Melipona. Thoracic vibrations and the concomitant pulsed sounds produced by successful M. Hrncir (&) Æ S. Jarau Æ F. G. Barth Biocenter, Institute of Zoology, University of Vienna, Althanstr.14, 1090 Wien, Austria E-mail: Michael.Hrncir@univie.ac.at Tel.: +43-1-427754470 Fax: +43-1-427754507 R. Zucchi FFCLRP, Department of Biology, University of Sa˜o Paulo, Avenida Bandeirantes 3900, 14040-901 Ribeira˜o Preto, SP, Brasil J Comp Physiol A (2004) 190: 539–548 DOI 10.1007/s00359-004-0514-7