In most lower termites, colonies produce a neotenic caste when either or both sexes of the reigning reproductives died. The produced neotenics begin reproduction with the reigning reproductive or the neotenics produced at the same time. Thus, the social role of neotenics is assumed as a reproductive caste in termites.

Neotermes koshunensis shows unusual neotenic system. This species shows exclusive maleness in the neotenic caste. Furthermore, the male neotenics are produced only in the orphaned colony. Thus, it seems that no opportunity of reproduction is given to male neotenics in this species. This phenomenon makes the social role of neotenics in this species be puzzling. We approached this problem by studying about the reproductive ability based on the histological observation and the rearing experiment.

We found no spermatozoid nucleus was found in many neotenics collected from field, whereas it was found in dealate reproductives. In the rearing experiment for 360 days, the male neotenic and the female dealate pairs produced less offsprings than the male dealate and the female dealate pairs. These results suggest the male neotenic in this species have lower reproductive ability than the male dealate reproductive's own.