Ultrastructural changes accompanying secretion and cell death in the molting glands of an insect (Oncopeltus)

During the fifth (last) larval instar of Oncopeltus fasciatus, morphological changes in the molting glands associated with ecdysone secretion include an increase in cytoplasmic volume relative to that of the nucleus, increased amounts of rough endoplasmic reticulum and mitochondria, and the formation of deep infoldings of the plasma membrane. On the sixth day of the fifth instar large electron-lucent areas become apparent beneath the basement membrane; however, the glands remain intact until the seventh (last) day of the instar when a dramatic fragmentation of the cytoplasm, and condensation and fragmentation of the nucleus are observed. It is likely that such changes occur rapidly, just prior to the time of ecdysis to an adult. Cell death in the molting glands of Oncopeltus is markedly different from that described for the molting glands of other insect species in that autophagic vacuoles are not observed prior to a complete loss of cellular integrity.