Endothermy and energy metabolism of a giant tropical fly,Pantophthalmus tabaninus thunberg

Abstract

1. Rates of oxygen consumption (\(\dot V_{{\text{O}}_{\text{2}} } \)), head, thorax and abdominal temperatures (Thd,Tth andTab) and wingbeat frequencies (WBF) were measured in individuals ranging in mass from 0.914 to 2.796 g. 2. The flies never attempted to fly unless disturbed. They frequently became endothermic withTth rising by 1 to 10°C even in the absence of overt activity. This was especially marked at dusk (Figs. 1, 2, 3). 3. Minimum daytime\(\dot V_{{\text{O}}_{\text{2}} } \) of 10 motionless ectothermic individuals (mean mass, 1.746 g, ambient temperature 26°C) was 0.577 ml O2/h. 4. \(\dot V_{{\text{O}}_{\text{2}} } \) of flies walking on a treadmill (0.5–1.7 cm/s) was not correlated with tread speed, probably because of the endothermic response which invariably occurred (Fig. 4). 5. During tethered flightTth rose by 0.1°C/s to above 40°C and remained stable (±0.1°C) until wingbeating stopped.\(\dot V_{{\text{O}}_{\text{2}} } \) increased 40–50 fold.\(\dot V_{{\text{O}}_{\text{2}} } \) before and after flight did not differ (Fig. 5). 6. During tethered flight bothTab andThd increased, withThd trackingTth more closely.Tth fell immediately after cessation of wingbeating, butThd rose sharply andTab continued to rise slowly (Figs. 6, 7). 7. At a givenTth in association with tethered flight,\(\dot V_{{\text{O}}_{\text{2}} } \) was often 6–10 times greater during warm-up than during cooling (Fig. 8). 8. WBF was relatively independent ofTth (Q10=1.25; Fig. 9). Mean WBF at aTth of 39.5°C was 139.8 Hz. Mean wing-loading was 0.6 g/cm2.