CARBOHYDRATE AND LIPID-METABOLISM DURING THE LAST LARVAL MOLT OF THE TOBACCO HORNWORM, MANDUCA-SEXTA

At 25-degrees-C and with a light regime of 17 h light and 7 h dark, th e last larval moult of the tobacco hornworm, Manduca sexta, lasts appr oximately 32 h, during which profound changes of metabolism were obser ved. At the onset of the moult, which coincides with the cessation of feeding, the proportion of active fat body glycogen phosphorylase incr eased from 10 (-2 h) to 25-30% (0 h). A biphasic pattern with peak act ivities of 45-50% after t = 12 h and again just prior to the shedding of the cuticle (32 h) was subsequently observed. Haemolymph trehalose concentration decreased significantly from c. 35 (0h) to 20 mm (8h), b ut then recovered to an intermediate level (30 mm; 12 h). After comple tion of the moult, the trehalose concentration was 35-40 mm. The haemo lymph glucose level in feeding fourth instar larvae was 4-5 mm, but de creased sharply before the onset of the moult to c. 1 mm, followed by a slow 6-fold increase over the next 20 h. Prior to the shedding of th e cuticle, the glucose level dropped again dramatically. The haemolymp h lipid level increased slowly from an initial level of 1.2-1.4 mg/ml during the early part of the moult, reaching a maximum of 1.8 mg/ml af ter t = 16 h. Afterwards, a decrease of c. 50% was observed until ecdy sis occurred. Oxygen consumption per animal decreased steadily from 30 -35 mul/min pre-moult by approximately 70% to c. 10 mul/min but starte d to increase about 5 h before the animals resumed feeding.