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

Summary

• 1. Rates of oxygen consumption ($\dot V_{{\text{O}}_{\text{2}} }$), head, thorax and abdominal temperatures (T _hd,T _th andT _ab) 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 withT _th 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 flightT _th 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 bothT _ab andT _hd increased, withT _hd trackingT _th more closely.T _th fell immediately after cessation of wingbeating, butT _hd rose sharply andT _ab continued to rise slowly (Figs. 6, 7).

• 7. At a givenT _th 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 ofT _th (Q₁₀=1.25; Fig. 9). Mean WBF at aT _th of 39.5°C was 139.8 Hz. Mean wing-loading was 0.6 g/cm².