Developmental Pathways and Polyethism of Neuter Castes in the Processional Nasute Termite Hospitalitermes medioflavus (Isoptera: Termitidae)

Abstract

The developmental pathways of neuter castes in the processional nasute termite Hospitalitermes medioflavus, which has monomorphic soldiers and trimorphic workers, was examined. Hospitalitermes is one of the genera of Nasutitermitinae which make processional foraging columns. The castes engaged in foraging are soldiers, and minor, medium and major workers. Sex determination by dissection and histological staining showed that soldiers and minor workers were males, while medium and major workers were females. In larval head width, three well-defined size peaks in the frequency distribution were found. The smallest peak consisted of both males and females of the first instar. The intermediate and largest peaks consisted respectively of males only and females only, of the second instar. Molting individuals and observations of mandibles confirmed the developmental relationships among castes. We concluded that the developmental pathway of the neuter castes in H. medioflavus is parallel to that found in Nasutitermes. Males change tasks from gnawing food (as minor workers) to defense (as soldiers), whilst females specialize in foraging (gnawing and carrying food). Division of labor during foraging depends primarily on sex and the developmental stage of neuter castes. This species thus displays both temporal and sexual polyethism.