Ultrastructure and respiration of the fat body of diapausing and non-diapausing larvae of the corn borer,Diatraea grandiosella

A comparative study of the fat body of diapausing and non-diapausing larvae of the corn borer, Diatraea grandiosella, was undertaken using the electron microscope and the oxygen electrode. The electron microscopic results showed a shift from a synthetic to a storage function taking place in a 1 to 2 day period during the final instar of non-diapausing larvae, and in a 4 to 8 day period in that of pre-diapausing larvae. This transition was characterized by a decrease in the number of mitochondria and amount of rough endoplasmic reticulum, and by an increase in the number of proteinaceous granules and lysosomes. In vitro measurements using the oxygen electrode showed that the fat body is a normal aerobic respiratory tissue. The tissue reacted in a predictable manner to inhibitors of oxidative metabolism, including malonate, rotenone, oligomycin, and antimycin, and to the uncoupler, dinitrophenol. During the last instar the observed decrease in the respiratory rate of the fat body coincided with the observed ultrastructural changes in its cells. The fat body of 75 day old environmentally induced and juvenile hormone induced diapausing larvae consumed 90% and 78% less oxygen, respectively than that of 14 day old non-diapausing larvae.