Temperature Regulation, Endothermy, Resting Metabolism, and Flight Energetics of Tachinid Flies (Nowickia sp.)

Thoracic temperatures (Tth) of the tachinid flies Nowickia nitida Wulp and N. rostrata Tothill averaged 29.8 C during activity at low ambient temperatures (Ta) at a highaltitude field site (elevation 3,800 m). The Tth ranged from 6.9 to 23.8 C above Ta, and the minimum Ta for flight was 5-8 C. In the laboratory the flies were capable of rapid endothermic warm-up with Tth increasing at a mean rate of 2.59 C/min. Occasional individuals maintained elevated Tth for long periods (10-15 min) without attempting to fly. Rates of oxygen consumption (V̇o2) of resting flies were similar to those of other insects and increased with increasing body temperature (overall Q10 between 2.5 and 40 C was 2.26). Oxygen consumption of flying Nowickia (approximately 53 ml/[g ․ h]) was lower than flight V̇o2 for strongly endothermic moths and bees but was sufficient to account for the large Tth − Ta difference observed during flight. Low flight V̇o2 in Nowickia may be related to relatively low wing loading (170 mg/cm²). The ability of Nowickia to fly at low Ta is partially explained by their low minimum Tth for flight (about 21 C). Nowickia can generate the necessary increase in Tth for flight at low Ta solely by endothermy, but the flies avoid some of the high energy costs associated with endothermy by basking when suitable microhabitats are available.