MANDIBULAR GLAND SECRETIONS MAKE BEES DEFENSIVE

Abstract

Most bees are famed for their stings, but not Meliponini. They have almost done away with their sting and resort to other alternatives for defence, such as nipping with their powerful mandibles. The stingless bees also produce pheromones from glands situated close to their mandibles. The secretions certainly seem to encourage stingless bees to defend themselves, but whether the mandibular gland secretions also attract the bees to rich nectar supplies has been hotly debated. Curious to find how the secretions function, Dirk Louis Schorkopf, working with colleagues from the University of Vienna and the University of São Paulo, investigated the mandibular secretions from two stingless bee species (Trigona spinipes and Scaptotrigona aff. depilis)(p. 1153).Analysing the composition of the secretions, the team found that they are complex. T. spinipes' mandibular gland secretions comprise at least 31 components, while S. aff. depilis' secretions comprise at least 27 components. The secretions of the two species also share 10 compounds, including the major component 2-heptanol, possibly allowing bees from the two species to communicate. Schorkopf explains that this makes sense because both species share the same habitat and probably compete for food.Testing the pheromones' effects on the bees, Schorkopf and his colleagues found that the pure mandibular gland secretions, and their individual components, caused the bees to behave defensively when the insects chose to respond. However, the team could not find any evidence that the bees used the pheromones to lay scent trails to rich nectar supplies. `While confirming the role of the mandibular glands in nest defence, our experiments provide strong evidence against their role in food source signalling,' says Schorkopf.