Lipid composition of fat body and its contribution to the maturing oocytes in Pyrrhocoris apterus

Abstract

The fat body of adult, female Pyrrhocoris apterus undergoes cyclic growth and diminution correlated with cycles of oocyte maturation. At all stages lipid accounts for 80 per cent of the dry weight of the fat body and the content of lipid, protein, and glycogen change in proportion to the changes in dry weight. The fatty acid composition of the lipid in fat body, ovaries, the whole insect, and the diet was examined by gas-liquid chromatography. Pyrrhocoris is similar to other insects in having triglyceride as the predominant class of lipid in the fat body but is distinctive in having an unusually high (more than 50 per cent) proportion of linoleate among its fatty acids, presumably owing to its diet. Reasons are presented for considering that little, if any, fatty acid is synthesized by the fat body and the ovaries during the reproductive cycle.During the first 5 days after the larval-adult ecdysis the Pyrrhocoris fat body first accumulates lipid and then releases it for utilization by the ovary. This temporary storage by the fat body compensates for the apparent inability of the insect to ingest a sufficient amount of lipid during vitellogenesis. The ovary normally utilizes dietary lipid as well during vitellogenesis; when the dietary supply was experimentally interrupted the amount of lipid released by the fat body increased. Storage of lipid in the fat body represents an important physiological adaptation since it frees the insect from dependence on a constant food supply during vitellogenesis.