UTILIZATION OF SUBSTRATES DURING TETHERED FLIGHT WITH AND WITHOUT LIFT GENERATION IN THE AFRICAN FRUIT BEETLE PACHNODA-SINUATA (CETONIINAE)

We have investigated the pattern of metabolic changes during tethered flight with and without lift generation in the African fruit beetle Pa chnoda sinuata. Two distinct metabolic phases occur during lift-genera ting flight. The first phase is characterised by a high rate of oxygen consumption and a rapid change in proline and alanine levels in the h aemolymph and flight muscles and in glycogen level in the flight muscl es. Carbohydrates are released from the fat body into the haemolymph. These carbohydrates are oxidised during the second phase. Changes in p roline and alanine levels in the haemolymph and flight muscles and in glycogen level in the Right muscles are minor during the second phase and the rate of oxygen consumption is reduced. During lift-generating flight, metabolic changes are rapid. Proline concentrations in the hae molymph and flight muscles fall dramatically during the first 30 s of Right, while alanine concentrations rise concomitantly. While haemolym ph concentrations of proline and alanine remain virtually unchanged th ereafter, further changes in the levels of these amino acids occur in the flight muscles during 5 min of flight. The initial levels of the t wo amino acids in the flight muscles are re-established over Ih of res t following a 5 min flight, while this process takes longer in the hae molymph. The concentration of haemolymph carbohydrates increases durin g the first 30 s of flight and declines thereafter during 5 min of Rig ht. The pre-Right levels are restored after Ih of subsequent rest. The stores of glycogen in the flight muscles are rapidly diminished durin g the first 10 s of flight and decrease at a lower rate during further flight lasting up to 5 min. A subsequent Ih of rest is sufficient alm ost to restore pre-Right levels. Haemolymph lipid levels are slightly but significantly increased during 11 min of flight and after 1 h of s ubsequent rest. During flight without lift production, the metabolic c hanges are considerably slower and beetles fly approximately seven tim es longer than during lift-generating flight. Resting basalar (BM), do rso-ventral (DVM) and dorso-longitudinal (DLM) flight muscles show no differences in levels of proline, alanine and glycogen, After differen t periods of flight, during which lift and wing loading were minimised , the DVM was found to have the highest level of proline after 5 min o f flight. Levels of alanine in the DVM were fewer than in the DLM. The re was no evidence to suggest that different flight muscles are specia lised for either proline or carbohydrate utilisation. Proline and carb ohydrates participate equally in supplying energy to the flight muscle s during lift-generating flight. The contribution to the energy supply by the flight muscles is 54 %, while that of the haemolymph is 46 %.