Sites of Synthesis and Transport Pathways of Insect Hydrocarbons: Cuticle and Ovary as Target Tissues

SYNOPSIS. The outer surface of insects is covered with a lipidlayer that provides water-proofing and protection against environmentalstresses. Hydrocarbons (HC) are major constituents of this epicuticularwax and they also serve as semiochemicals. In some insects HCare also exploited as biosynthetic precursors for pheromones.HC are synthesized by oenocyteswhich are situated in the integumentor hemocoel. Shuttling of HC to the epicuticie, fat body, andgonads requires transport through an aqueous medium. Insects,unlike vertebrates, use a versatile lipoprotein to effect lipidtransport and to selectively deliver lipids to specific tissues.A high-density hemolymph lipoprotein (lipophorin [Lp]) servesthis function.In adult females of the German cockroach (Blattellagermanica), Lp carries both HC and a contact sex pheromone.Lipophorin is a multi-functional lipid carrier serving alsoas a juvenile hormone binding protein in many insects. Studiesofthe interactions between Lp and HC are beginning to unravelthe routes used in delivering HC to target tissues. We discussthepathways and dynamics of loading of Lp with HC and HC-derivedpheromones, their transport through the hemolymph, and depositionin various tissues, including the epicuticie, ovaries, and pheromone-emittingglands.