Direct calorimetric measurement of heat production rates in flying hornets(Vespa crabro; Hymenoptera)

Heat production rates of Eying hornet drones, workers and queens have been measured by means of direct calorimetry. A novel kind of calorimeter includ ing a flight roundabout, to which insects can be fixed, has been constructe d for this purpose. Heat production rates of flying drones and workers show ed a weak negative correlation with ambient temperature. Mean specific heat production rates for workers were 159+/-38 mW g(-1) at 20 degrees C and 10 3+/-44 mW g(-1) at 30 degrees C, and for drones 119+/-27 mW g(-1) at 20 deg rees C and 70+/-23 mW g(-1) at 35 degrees C, The same weak negative correla tion with ambient temperature could be shown for flight speed, whereas wing -beat frequencies were independent of temperature with values between 85 an d 97 Hz. Methodical limitations are discussed in the application of direct calorimetry for flight investigations as well as in some biological implica tions of our results, (C) 1999 Elsevier Science B.V. All rights reserved.