ENERGY SUBSTRATES FOR FLIGHT IN THE BLISTER BEETLE DECAPOTOMA-LUNATA (MELOIDAE)

We investigated the substrates for flight in the blister beetle Decapo toma lunata by (a) establishing the patterns of maximum activities of enzymes of various metabolic pathways in the Right muscles, (b) measur ing the respiratorg rates of flight muscle mitochondria with various s ubstrates and (c) determining metabolite concentrations in flight musc les and haemolymph during a flight period of up to 17 min and over a r est period of up to 2 h following 10 min of flight. Activities of enzy mes involved in proline metabolism (glutamate dehydrogenase, alanine a minotransferase, malic enzyme) were much higher in the blister beetle than in the migratory locust Locusta migratoria, whereas the activity of an enzyme responsible for fatty acid oxidation (beta-hydroxyacyl-Co A dehydrogenase) was much lower. Mitochondria from flight muscles of D . lunata have a much higher capacity to oxidise proline than those fro m L. migratoria, The glycerophosphate shuttle, however, was equally ac tive in both insects. Whereas lipid levels in the haemolymph did not c hange significantly during flight, there was a continuous decrease in proline levels from 34.8 to 6.6 mu mol ml(-1) and a simultaneous incre ase in alanine concentration; carbohydrate levels dropped from 20.1 to 12.2 mg ml(-1). In the thorax (flight muscles), glycogen levels were diminished between 2 and 17 min of flight from 25.9 to 6.7 mu mol gluc ose equivalents g-l fresh mass, Proline concentration dropped continuo usly from an initial 49.5 to 10.1 mu mol g(-1) fresh mass, whereas ala nine levels rose concomitantly from 2.9 to 17.3 mu mol g(-1) fresh mas s. After termination of a 10 min Right, pre-Right levels of proline in the haemolymph and flight muscles were only reestablished after 2 h, In contrast, glycogen levels in the thorax were restored after 1 h, Us ing the rates of utilisation of substrates during the first 10 min of flight to calculate rates of oxygen consumption during flight, it was shown that overall haemolymph substrates contribute 75 % and those of the flight muscles only 25 %, Although proline is an important substra te for flight in D. lunata, its role is secondary to that of carbohydr ates, This type of substrate usage is different from that of the Color ado potato beetle Leptinotarsa decemlineata or the African fruit beetl e Pachnoda sinuata, in which carbohydrates are of negligible or only s light importance, respectively.