Mandibular morphogenesis during soldier differentiation in the damp-wood termite Hodotermopsis sjoestedti (Isoptera: Termopsidae)

The conspicuous morphogenesis during termite soldier differentiation is one of the most remarkable examples of specialized caste development in social insects. To clarify the mechanism of morphological changes during soldier differentiation, mandibular morphogenesis prior to the presoldier moult was examined in the damp-wood termite Hodotermopsis sjoestedti. Using experimental induction of presoldier differentiation from pseudergates (7th or later instar larvae) by the application of juvenile hormone analogue (JHA), we compared mandibular morphogenesis in a presoldier moult (from pseudergate to presoldier) with that of a stationary moult (from pseudergate to pseudergate). Future presoldier mandibles were formed under the old mandibular cuticle of the pseudergates just prior to the presoldier moult. Multiple folds of both epidermis and new cuticle were observed in the developing mandible, and large concavities between teeth were formed on the mandibular surface. While in the stationary moult, the future mandibles were formed with a smooth surface. The process of the mandibular morphogenesis in soldier differentiation explains the allometry of soldier mandibles. The morphological differences in mouth parts between castes arise from a switching mechanism that triggers caste-specific mandibular epithelial growth during development.