Relationships between frontal-gland formation and mandibular modification during JH III-induced presoldier differentiation in the termite Reticulitermes speratus (Isoptera: Rhinotermitidae)

Termite soldiers engage in colony defense and they possess weapons in order to attack enemies. Defensive strategies vary among species depending on the morphology of the soldier's weapons. Both the frontal gland and elongated mandibles are formed during soldier differentiation of Reticulitermes speratus workers, which is associated with an increase in juvenile hormone (JH) titer. It was shown that the amount of JH applied and coexistence with soldiers affected mandibular elongation of the induced presoldiers. To determine the relationship between applied JH concentration and frontal-gland development of R. speratus, mandibular modification and frontal-gland formation of presoldiers induced by 20, 40 and 80μg JH III in the presence or absence of soldiers were observed. Both presoldier differentiation rates and their mandibular lengths were affected by the presence of soldiers in treatments with 20 and 40μg JH III. Especially in the treatment with 20μg JH III, frontal-pore malformation was observed in some presoldiers. All presoldiers with a malformed frontal pore had almost the same sized mandibles, compared with those of stationarily molted workers. Interestingly, sections of these presoldiers showed that frontal-gland invagination occurred incompletely in comparison with presoldiers with relatively elongated mandibles. Consequently, frontal-gland formation might be affected by JH titer (applied and endogenous JH), and individuals with a malformed frontal pore were probably differentiated by JH titers only slightly above the threshold for presoldier differentiation.