Lipids comprise significant components in insect nutrition. Definite requirements for lipids in the diet of insects have been stressed by several authors, indicating that--among other constituents—polyunsaturated fatty acids and sterols are essential. In addition, dietary lipids, particularly triacylglycerols, provide an important source of metabolic energy. Diacylglycerol release from insect fat body as a possible means of lipid transport in insects was first established by Chino and Gilbert in the silkmoth, Hyalophora cecropia. In the migratory locust it has long been recognized that the main source of energy for flight muscle contraction during sustained flight is diacylglycerol, which is mobilized from fat body triacylglycerol stores and transported in the haemolymph. Both the diacylglycerol released from triacylglycerol digestion in the alimentary tract and the diacylglycerol released from the fat body must be transported in the aqueous haemolymph and therefore are not present as free molecules, but rather as components of macromolecular lipoprotein complexes.