Presoldier differentiation of Australian termite species induced by juvenile hormone analogues

Abstract

Termite soldiers have species-specific defensive morphologies. High juvenile hormone (JH) titre is required for workers to moult into presoldiers (intermediates between workers and soldiers). Artificial inductions of presoldiers using JH or JH analogues (JHAs) have been conducted in many species, but levels of intergeneric and species-specific JH sensitivity are not clear. Here, we investigated mortality and presoldier induction rates after the same JHA treatments in three Australian termites: the rhinotermitids Coptotermes lacteus and Schedorhinotermes intermedius, and the early branching termite species Mastotermes darwiniensis. Induced presoldiers, especially in S. intermedius (soldiers with labral brush-like weapons), were used for the observation of outer morphologies using scanning electron microscopy. In C. lacteus, large numbers of presoldiers were induced by all JHAs examined, and the mortality rate of workers was quite high. On the other hand, presoldier induction rates were very low in S. intermedius and zero in M. darwiniensis. However, mortality rates of these two species were quite different. In M. darwiniensis, the numbers of dead individuals in almost all JHA-treated dishes were not significantly different from those of an acetone control. These results suggest that JHA sensitivity might be quite different among the three species, although further analyses using multiple colonies are needed to confirm this possibility. Scanning electron microscopy observation in S. intermedius showed that soldier-specific formations of frontal pores in the heads, including a median furrow running from the frontal pore to the apical part of the labrum, and many campaniform sensillae and short bristles at the end of the labrum were all initiated at the presoldier stage.