CARBOHYDRATE-METABOLISM IN MANDUCA-SEXTA DURING LATE LARVAL DEVELOPMENT

The carbohydrate metabolism in Manduca sexta underwent significant changes during late larval development. Approximately 10% of fat body glycogen phosphorylase was active during the feeding period of the 5th instar, pharate-pupal development and after the pupal moult; it is concluded that glycogen synthesis prevailed. During the last larval and the pupal moult, as well as the wandering stage percentage of active phosphorylase was significantly increased indicating that fat body glycogen stores were broken down to supply substrates to meet the demands of carbohydrate metabolism. In the course of the last larval moult and the wandering stage of the fat body glycogen content decreased significantly from about 300 to about 200 .mu.g mg-1 dry mass substantiate that carbohydrates were released from the fat body. Prior to phosphorylase activation, the concentrations of total haemolymph sugars decrease significantly from about 12 to abut 6 mg trehalose equivalents ml-1 (last larval moult) and from about 18 to about 12 mg ml-1 (wandering stage), and increased again slightly when phosphorylase was activated. The haemolymph glucose concentration decreased significantly from about 1.1 to 0.3 mg ml-1 (last larval moult) and in the course of the 5th-instar feeding period from about 1.1 to 0.2 mg ml-1, and remained at this level until the beginning of adult development. The amount of chitosan present in the cuticle increased steadily during the feeding period of the 5th instar from about 10 to 110 mg. It appears that fat body glycogen might be broken down during the last larval moult and the wandering period to provide substrates for chitin synthesis. A dramatic decrease in the amount of chitosan was observed prior to the pupal moult.