Figure 1. Aggression assay.

(a) Top view of the arena showing the location of the odourant and honeybee entry points, as well as the rotating dummy. (b) ‘Experimental data': percentage of trials in which at least one of the bee stung the dummy, recorded as a function of the odour present (TEC: solvent; IAA: alarm pheromone) and the number of bees introduced inside the arena. ‘Theoretical data': results expected if the two bees were acting independently from each other, calculated from the probability of attack of a single bee. χ² tests; NS, not significant; P>0.05, **P<0.01, n=32 single bees and 32 pairs of bees.