Effects of ambient temperature and humidity on internal temperature and wing-beat frequency of Periplaneta americana

Abstract

Internal thoracic temperature of Periplaneta americana males was measured at rest before flight, in flight, and at rest after flight at 25, 30, 35 and 40°C, and 50 and 95% r.h. The internal temperature at 50% r.h. was regularly below ambient temperature before flight and did not reach ambient temperature during flight at 35 and 40°C. Internal temperature at 95% r.h. was slightly below ambient temperature before flight at 30, 35, and 40°C, but the reduction was not as great as for 50% r.h. Maximum increase in thoracic temperature during flight was less at 50 than at 95% r.h. Internal temperatures lower than ambient are attributed to cooling through water loss. After flight thoracic temperatures dropped toward their pre-flight level. At 50% r.h. internal temperature 5 min after cessation of flight was approximately the same as the pre-flight temperature, but at 95% r.h. the internal temperature 5 min after flight ended was consistently higher than the pre-flight temperature. Wing-beat frequencies during flight of males with a thermocouple inserted in the thorax were the same as frequencies obtained from males without a thermocouple in the thorax. Internal thoracic temperature and wing-beat frequency were related but not closely correlated. From 30 to 40°C ambient the wing-beat frequencies at a given internal temperature were higher at 95 than at 50% r.h. During the warm-up portion of flight, prior to reaching equilibrium flying temperature, there was no appreciable increase in wing-beat frequency even though the internal temperature increased approximately 1·5 to 3·5°C. These examples of variation of wing-beat frequency that are not predictable from internal temperature indicate an additional mechanism influencing wing-beat frequency.