Fat Body During Development And Metamorphosis

During the period of metamorphosis the fat body tissue undergoes extensive morphological, histological, biochemical, and organizational changes. These processes are triggered by the molting hormone on the background presence of extremely low levels of the JH. Such alterations have been thoroughly studied in dipterans and lepidopterans. Two major strategies for transforming the larval fat body into an adult tissue exist: (1) the histolytic pathway, in which the larval fat body adipocytes in dipteran species are completely histolyzed and the adult new tissue is formed from undifferentiated stem cells, and (2) the remodeling pathway, in which adipocytes in the larval stage of lepidopteran insects dissociate at metamorphosis into individual cells before being reassociated into the adult new tissue. In certain holometabolous insect species, a combination of the two processes takes place.

Dynamic exchanges of nutrients between fat body cells and the hemolymph compartments are evident throughout the life cycle of holometabolous insects (Fig. 1). Buildup of reserves and their partial use at the molting periods are characteristic of the larval stages. During the prepupal period, mass quantities of reserve material are accumulated in the fat body cells. Lysis of fat body cells in higher dipteran species at metamorphosis results in the discharge of stored reserves into the hemolymph. However, as the new adult fat body cells are

Adipocytes Hemolymph

Stored reserves -►

Larval stages ^

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