ORIGINAL PAPER M. O. Scha¨fer Æ V. Dietemann Æ C. W. W. Pirk P. Neumann Æ R. M. Crewe Æ H. R. Hepburn J. Tautz Æ K. Crailsheim Individual versus social pathway to honeybee worker reproduction (Apis mellifera): pollen or jelly as protein source for oogenesis? Received: 16 October 2005 / Revised: 31 January 2006 / Accepted: 5 February 2006 Ó Springer-Verlag 2006 Abstract Honeybee workers, Apis mellifera, can repro- duce in queenless colonies. The production of queen-like pheromones may be associated with their reproductive activity and induce nestmates to respond by feeding them. Such frequent trophallaxis could supply their protein needs for oogenesis, constituting a social path- way to worker reproduction. However, some individuals can develop ovaries without producing queen phero- mones. The consumption of protein-rich pollen could be an alternative solitary pathway for them to satisfy this dietary requirement. In order to investigate the way in which workers obtain proteins for oogenesis, we created orphaned worker groups and determined ovarian and pheromonal development in relation to pollen con- sumption of selected workers. Individuals that did not consume pollen had significantly more developed ovaries and produced significantly more queen mandibular pheromone than workers that fed directly on pollen. Our results suggest that workers producing queen-like secretions are fed trophallactically. However, reproductive workers that lacked queen pheromones had consumed little or no pollen, suggesting that they also obtained trophallaxis. Although pollen consumption might con- tribute to sustaining oogenesis, it does not appear to be sufficient. Trophallaxis as a means of obtaining proteins seems to be necessary to attain reproductive status in queenless honeybee colonies. Keywords Honeybees Æ Worker reproduction Æ Pheromonal dominance Æ Trophallaxis Æ Pollen consumption Introduction One of the major characteristics of social Hymenoptera is the division of reproductive labour between two female castes: the queens and the workers. Generally, one or only a few queens lay eggs while workers supply food and maintain the nest. However, in most species the workers are capable of reproducing when the queen is removed (Bourke 1988; Choe 1988; Hoover et al. 2003). Independent of caste, individuals that reproduce require proteins to sustain oogenesis (Wheeler 1996). In the honeybee, Apis mellifera, pollen is the main source of protein (Grogan and Hunt 1979) and workers metabo- lise it to produce royal jelly (Crailsheim et al. 1992). This jelly is fed to the queen by trophallaxis (the exchange of liquid food or glandular secretions among nestmates, Wilson 1971) and this fulfils all of her nutritional requirements, including proteins for oogenesis (Allen 1955, 1960; Haydak 1970; Rutz and Lu¨scher 1974; Crailsheim 1991; Free et al. 1992). Queen honeybees produce specific pheromones to attract a retinue of workers that care for their needs. The main source of these pheromones is the mandibular gland and the main compound produced by queens is (E)-9-keto-2-decenoic acid (9-ODA, Barbier and Lederer 1960; Slessor et al. 1988). The major compound produced in workers’ mandibular glands is 10-hydroxy- (E)2-decenoic acid (10-HDA, Callow et al. 1959; Pankiw M. O. Scha¨fer (&) Chemisches und Veterina¨runtersuchungsamt Freiburg, Am Moosweiher 2, 79108, Freiburg, Germany E-mail: mos.mellifera@gmx.de V. Dietemann Æ C. W. W. Pirk Æ R. M. Crewe Department of Zoology and Entomology, University of Pretoria, 0002, Pretoria, South Africa P. Neumann Institut fu¨ r Zoologie, Martin-Luther-Universita¨ t Halle-Wittenberg, Hoher Weg 4, 06099, Halle (Saale), Germany H. R. Hepburn Æ P. Neumann Department of Zoology and Entomology, Rhodes University, 6140, Grahamstown, South Africa J. Tautz Bee-group, Biozentrum der Universita¨t Wu¨rzburg, Am Hubland, 97074, Wu¨rzburg, Germany K. Crailsheim Institut fu¨r Zoologie, Universita¨t Graz, Universita¨tsplatz 2, 8010, Graz, Austria J Comp Physiol A (2006) DOI 10.1007/s00359-006-0112-y