Proline powers pre-flight warm-up in the African fruit beetle Pachnoda sinuata (Cetoniinae)

摘要

We investigated thoracic temperatures (T-th) 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 T-th prior to take-off either by basking in the sun or by warming endothermically to a narrow range around 34 degrees C. During lift-generating tethered flight at low ambient temperatures (T-a=25 degrees C), T-th of P. sinuata decreases steadily until it reaches 28 degrees C, which is not sufficiently high to sustain flight. T-th remains stable during lift-generating tethered flight at high T-a (31 degrees C), Wingbeat frequency (f(w)) is dependent on T-th: when T-th declines, f(w) 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. [References: 28]