Histological analysis of fat body development and molting events during soldier differentiation in the damp-wood termite, Hodotermopsis sjostedti (Isoptera, Termopsidae)

The caste system of termites is well defined, with a high degree of polyphenism among colony members. Polyphenic caste characteristics are hormonally regulated, and juvenile hormone (JH) is particularly involved in caste determination, as is the case with many other social insects. In the present study, soldier differentiation in the damp-wood termite, Hodotermopsis sjostedti, was induced by treatment with a JH analog (pyriproxyfen) in order to establish the chronology of tissular modifications appearing in response to the hormone. The fat body is involved in the physiological events that prepare the insect for the molting transition. The development of the fat body started within three days after hormonal treatment, and it filled the entire abdominal cavity for about four days prior to the molt to presoldier, maintaining this state until the next molt to soldier. Fat body development was accompanied by the accumulation of protein granules in the cytoplasm, but these granules disappeared during the few days preceding the molt to presoldier. The timing of consumption of these storage proteins corresponded to the window of epidermal growth, which was conspicuous about 14 days after hormonal treatment, and synthesis of the new cuticle, which was initiated 10 days after treatment. We summarize the chronology of the histological events under hormonal control.