Soldier differentiation and larval juvenile hormone sensitivity in an incipient colony of the damp-wood termite Zootermopsis nevadensis (Isoptera, Termopsidae)

In the incipient colonies of termites, only one soldier normally emerges and is maintained for a long time. This soldier is differentiated from younger instar larvae that are much smaller than soldiers in the mature colonies. Here we used Zootermopsis nevadensis for the incipient colony foundation, and tried to detect the differences of juvenile hormone (JH) sensitivities between young larvae from the incipient and mature colonies. Firstly, larval pronotum and head widths were measured, and the 3rd and 4th stages of larvae that are suggested to be differentiated into presoldiers at the incipient colony. Then, the rates of presoldier differentiations induced by juvenile hormone analog (JHA) were compared between 3rd and 4th stages of larvae from incipient and mature colonies. Soldier differentiation was shown to be suppressed when the larvae from the incipient colony were treated with both quantities of JHA (0.1 and 1 μg per 1 dish). Thus, larvae in the incipient colony are suggested to be less sensitive to JHA than those in the mature colony. The cross-section sizes of the corpora allata in the 4th-instar larvae picked-up from the incipient colony were shown to be significantly smaller than those from the mature colony. This suggests that JH titers in the incipient-colony larvae are lower than those in the mature-colony larvae, possibly due to the lower level of the nutritional condition, or reduction by the members in the same colony.