Behavioural patterns of pseudergates, nymphs and replacement reproductives were observed in laboratory colonies of Kalotermes flavicollis with different social composition. The investigation revealed that in presence of the royal couple, pseudergates and nymphs behave similarly, acting as typical workers and confirmed the central role of the reproductives in receiving and transmitting signals which probably underlie the regulation of social equilibrium. The death of a reproductive, which occurred spontaneously in two pseudergate colonies, gave rise to a remarkable increase of activities, especially of social interactions among pseudergates.