Figure 1.

Intentional (signal) and unintentional (cue) information transfer in the European beewolf Philanthus triangulum and the honeybee A. mellifera. Defining a substance as a cue or signal depends on the selective pressures under consideration. (Z)-11-Eicosen-1-ol functions as signal or cue according to the multiple selection pressures acting upon it. As a major compound of an alarm pheromone in the sting apparatus of honeybees, it is selected as an intraspecific signal to lure conspecifics to the site of emission for concerted defence behaviour. It also prolongs the activity of the more volatile isopentyl acetate, a further compound of the alarm pheromone [20,21]. Emitting (Z)-11-eiconsen-1-ol from a reservoir appears thus to be adaptive for honeybee workers. It is thus a signal that is selected because it increases the fitness of its sender. At the same time, traces of this alcohol spread over the cuticle of honeybee workers causing a permanent smell. Female beewolves exploit this smell as a cue to identify their prey [22,23]. Remarkably, the use of a chemical cue during foraging impinges on the epigamic communication system among beewolf mates. Beewolf males apparently exploit the sensory biases that females exhibit to locate their prey by producing a pheromone to attract females that mainly consist of (Z)-11-eicosen-1-ol [24]. The males produce this compound in a large postpharyngial gland and scent mark small territories on a lek, which are defended against conspecific males [25]. Thus, sensory exploitation of cues used in a different context can trigger the evolution of intraspecific sexual communication to facilitate mate location. Photographs reproduced with permission from Martin Kaltenpoth (male beewolf), Gudrun Herzner (female beewolf) and Claudia Gack (honeybee).