Proline powers pre-flight warm-up in the african fruit beetle pachnoda sinuata

We investigated thoracic temperatures (Tth) during different activities of the endothermic fruit beetle Pachnoda sinuata and analysed which energy substrates are used for the pre-flight warm-up of its flight muscles. Pachnoda sinuata elevates its Tth prior to take-off either by basking in the sun or by warming endothermically to a narrow range around 34 degreesC. During lift-generating tethered flight at low ambient temperatures (Ta=25 degreesC), Tth of P. sinuata decreases steadily until it reaches 28 degreesC, which is not sufficiently high to sustain flight. Tth remains stable during lift-generating tethered flight at high Ta (31 degreesC). Wingbeat frequency (fw) is dependent on Tth: when Tth declines, fw decreases in a linear manner. The proline concentrations in the haemolymph and flight muscles decrease during warm-up. In contrast, the carbohydrate levels in the haemolymph and flight muscles are not affected by the warm-up process, while the glycogen level of the flight muscles declines significantly during the first 10 s of lift-generating tethered flight. This suggests that the energy for endothermic warm-up is produced solely by the oxidation of proline. Measurements of the respiratory quotient (RQ) confirmed that P. sinuata uses a combination of carbohydrates and proline to power its flight. At rest and during lift-generating tethered flight, the RQ is approximately 0.9. During warm-up, the RQ is significantly lower at 0.82, which is close to the theoretical value of 0.8 for the partial oxidation of proline. The rate of oxygen consumption during endothermic warm-up is 45 % of that during lift-generating tethered flight