Male meliponine bees (Scaptotrigona aff. depilis) produce alarm pheromones to which workers respond with fight and males with flight.

In highly social hymenopteran societies, males mainly serve reproductive purposes. Semiochemicals enable the different hymenopteran sexes and castes to communicate with each other and to coordinate important functions within colonies. I hereby show that sexual dimorphism in meliponine bees incorporates the alarm and defence communication system. I chemically analysed the mandibular glands of Scaptotrigona aff. depilis using GCMS methods and conducted behavioural experiments in both males and female workers using cephalic and mandibular gland extracts. In addition, behaviour studies with male cephalic extracts were also conducted in Scaptotrigona bipunctata and Partamona cupira. Males and female worker bees showed differences in the content of the mandibular glands, which are responsible for alarm communication in meliponines. Males never attacked but usually fled when confronted with the mandibular gland extract content of other conspecific males or females. Interestingly, however, meliponine males were still able to raise alarm and to induce substantial amounts of aggression at nest entrances, which is different from the much better known and studied honey bees. Potential reasons are briefly discussed.