Metabolic changes in the African fruit beetle, Pachnoda sinuata, during starvation

Specimens of the fruit beetle Pachnoda sinuata were starved for up to 30 da ys. The weight of the beetles declined consistently throughout the starvati on period. Concentrations of carbohydrates and alanine in flight muscles, f at body and haemolymph decreased rapidly after onset of starvation, while t he concentration of proline remained high. Whereas the lipid concentrations in the haemolymph did not change significantly upon starvation, the lipid content in flight muscles and fat body decreased significantly. Beetles that had been starved for 14 days responded to injection of Mem-CC, the endogenous neuropeptide from its corpora cardiaca, with hyperprolinaem ia and a decrease in the alanine level, but no such effect was monitored af ter prolonged starvation of 28 days. Regardless of the period of starvation , Mem-CC injection could not cause hypertrehalosaemia or hyperlipaemia, alt hough carbohydrates were increased in fed beetles after injection. Flight ability of beetles that had been starved for 15 or 30 days was appar ently not impaired. During such periods, beetles used proline exclusively a s fuel for flight as evidenced by the increase in the level of alanine in t he haemolymph and decrease of the level of proline; the concentrations of c arbohydrates and lipids remained unchanged. Activities of malic enzyme and alanine aminotransferase (enzymes involved i n transamination in proline metabolism), glyceraldehyde-3-phosphate dehydro genase (enzyme of glycolysis), 3-hydroxyacyl-CoA dehydrogenase (enzyme of P -oxidation of fatty acids) and of malate dehydrogenase (enzyme of Krebs cyc le) were measured in fat body and flight muscles. In flight muscle tissue t he maximum activity of NAD(+)-dependent malic enzyme increased, while that of glyceraldehyde-3-phosphate dehydrogenase decreased during starvation, an d malate dehydrogenase, 3-hydroxyacyl-CoA dehydrogenase and alanine aminotr ansferase were unchanged. In fat body tissue, activities of NADP(+)-depende nt malic enzyme and 3-hydroxyacyl-CoA dehydrogenase increased during food d eprivation and activities of glyceraldehyde-3-phosphate dehydrogenase, mala te dehydrogenase and alanine aminotransferase remained unchanged. (C) 2000 Elsevier Science:Ltd. All rights reserved.