Age-Dependent Increase in Soldier Pheromone of the Termite Reticulitermes speratus

Pheromone communication helps maintaining the sophisticated colony organization in social insects. In the termite Reticulitermes speratus, there are two functionally distinct soldier groups: royal guards and entrance guards. Royal guards protect kings and queens in the innermost part of the nest, whereas entrance guards prevent predators from intruding into the nest at the periphery. A recent study revealed that younger and older soldiers work as royal and entrance guards, respectively. This age-dependent distribution is thought to help workers to recognize where in the nest they are located. However, it is not known whether workers can discriminate the age of soldiers. Here, we show that the abundance of soldier pheromone changes with age and that workers discriminate a soldier's age by recognizing the pheromone abundance. Gas chromatography-mass spectrometry analysis revealed that the chemical profiles of extracts in three soldier groups of different ages (newly differentiated, royal guard, and entrance guard soldiers) are markedly different. Entrance guard soldiers have the most soldier pheromone among the three age classes. Furthermore, our bioassays suggested that the worker's movement from chamber to chamber is inhibited only when a soldier with less soldier pheromone is located at the chamber entrance. These results suggest that the soldier pheromone functions as a soldier age indicator and that workers change their behavior depending on the age of the soldier defending the chamber entrance. This study contributes to our understanding of the relationship between aging and pheromone communication in social insects.