Honeybee nestmate recognition

protein (pollen) and energy resources (honey) in a stock. Beside the pollen and the brood, it is the honey that attracts not only robbers like man, other mammals (e.g. bears and badgers) and other insects (e.g. wasps) but also bees of their own species. That is why honeybees developed their typical guarding behaviour (Butler and Free, 1952; Moore et al., 1987). Their ability to produce endothermic heat by means of their flight muscles plays an important role in colony defence (Esch, 1960; Heinrich, 1979a; Ono et al., 1995). To defend their colony properly against other bees, guards are thought to need a higher or at least the same motility than the bees examined by them (examinees). The main parameter influencing the motility of honeybees is the thorax temperature. They use their highly developed endothermy (Esch, 1960; Heinrich, 1979a, 1993; Schmaranzer and Stabentheiner, 1988) to improve the function of their flight muscles (Esch, 1976; Coelho, 1991) and their general mobility (Stabentheiner et al., 1995; Stabentheiner and Crailsheim, 1999; Crailsheim et al., 1999). Therefore, we measured the body temperature of both the guards and the examinees simultaneously by real-time infrared thermography (Schmaranzer and Stabentheiner, 1988) without disturbing their interaction. The measurements show that guards and examinees differ considerably, and in an unexpected way, in their thermal behaviour. The observation of unexpected thoracic heating phases in the examinees led to several hypotheses about their biological significance. One suggestion was that examinees heat up to get rid of guards’ pheromones, which marks them as possible intruders. One substance that is known to have pheromonal function in honeybees and is suspected to be a marking pheromone is 2-heptanone from the mandibular glands (Shearer and Boch, 1965; Free, 1987). We tested 2-heptanone for its effect on the thorax temperature of bees. Guards examine other bees not only at the nest entrance but also inside the nest (Butler and Free, 1952; Stabentheiner, 1994). The behaviour of a guard examining a bee resembles to some extent the behaviour of grooming bees during social grooming interactions inside the colony. In order to see whether or not the thoracic heating phases of the examined bees also exist in groomed bees, that is, whether they are required for grooming, we measured the thorax temperature of bees performing grooming dances and of groomed and grooming bees.