Biochemical Correlates Of Pre-flight Warm-up In The Sphinx Moth, Manduca Sexta (enzymes, Carbohydrates).

Abstract

Endothermic insects can attain metabolic rates equalling or exceeding those of vertebrates of similar size, yet this endothermy is an intermittent phenomenon. These insects are ectotherms with typical ectothermic metabolic rates for most of their lives and their considerable metabolic capacity is inoperative. Pre-flight warm-up represents a metabolic as well as a thermal transition phase. Body composition and fuel stores were investigated in laboratory-reared adults of the moth, Manduca sexta. Body mass and whole body water, protein and lipid contents of moths fed 20% sucrose ad libitum were stable over the first five days of adult life. Males contained more lipid but lipid content was high in both sexes. Muscle carbohydrate stores were quantitatively small but were replenished through feeding activity. Feeding by adults accounts for most of the energy required for flight and reproduction under these conditions. Carbohydrate depletion at intermediate thoracic temperatures during pre-flight warm-up at 15(DEGREES)C was also investigated. Muscle glycogen declined from 3.177 mg/g muscle at rest to 2.569 mg/g at T(,th) = 21(DEGREES)C and did not decline further as warm-up continued. Muscle glucose and trehalose and abdominal glucose, glycogen and trehalose were unchanged. Glycogen depletion can account for about 4% of the total cost of warm-up and 20% of the initial phase. Activities of glycolytic, lipolytic and citric acid cycle enzymes were examined at 15(DEGREES)C, 25(DEGREES)C and 37(DEGREES)C. The muscle and fat body glycogen phosphorylases, trehalase and glycerol-3-phosphate dehydrogenase were temperature sensitive. Hexokinase, phosphofructokinase, 3-Hydroxyacyl-CoA dehydrogenase and citrate synthase were comparatively temperature-insensitive. The consequences of these thermal responses for the metabolic organization of muscle, fuel use during pre-flight warm-up and mechanisms contributing to metabolic reductions at rest are discussed.