Colony age-dependent pathway in caste development of Coptotermes formosanus Shiraki

The caste developmental pathway for the production of soldiers and nymphs in termite colonies is variable among species and limited numbers of studies have properly categorized such pathways. In this study, the developmental pathway for the production of soldiers and nymphs in Coptotermes formosanus Shiraki has been re-analyzed using the data from previous studies in light of new observations. Five distinct colony life stages were determined based on the caste developmental pathway used by the colony at each stage, which we here redefined as: incipient colony, immature colony, juvenile colony, mature colony, and senescent colony. We determined that in incipient colonies, the first soldier (nanitic) emerges from a second instar larva. We suggest that the production of a nanitic soldier is cost-effective as it allows the colony to focus on the production of workers from the first cohort of individuals. However, in an immature colony, the origin for the production of soldiers shifts to first and second instar workers. In juvenile colonies, soldiers are essentially produced from second instar workers. In mature colonies (>5 years), soldiers are mostly produced from second instar workers, occasionally from third instar workers, and we suggest that nymphs are primarily produced from second instar larvae. Finally, in senescent colonies, the absence of brood leads to the accumulation of old individuals. We concluded that descriptions from previous studies may have overlooked the group dynamics within a colony and that the caste developmental pathway in C. formosanus is dependent on the age of the colony.