Changes in temperature and light alter the flight speed of hornets (Vespa crabro L.).

Although the principal mechanisms of insect flight are well understood, knowledge about the influence of environmental factors on flight performance is scarce. We show that ambient temperature (TA) and illuminance have an influence on the flight performance of hornets. Moreover, the regulation of flight speed at different environmental conditions is sex specific. In roundabout experiments with tethered hornets, the flight speed of workers was independent of TA, while that of drones was negatively correlated with TA. We hypothesize that the reasons for these differences may lie in sex-specific cooling mechanisms; workers might regulate their body temperature through forced heat loss, whereas drones might reduce their heat production rates. At low illuminance, workers reduced their flight speed, whereas drones did not. Reduced flight speed at low illuminances is probably a behavioral mechanism of compensation for disadvantages caused by changing neuronal processes in the sensory neurons in darkness.