Changes in Temperature and Light Alter the Flight Speed of Hornets (Vespa crabroL.)

Abstract

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.

Effect of light intensity on flight control and temporal properties of photoreceptors in bumblebees

“…Flight speed decreased more or less linearly in response to a logarithmic decrease in light intensity. This result is consistent with the findings of a previous study, which showed that tethered hornets fly slower in dim light (Spiewok and Schmolz, 2006). In that study, the flight speed of hornets was measured at three different light intensities, similar to the ones used in our study (850, 5 and 0.5 lx).…”

“…Earlier experiments on vertebrates (Barlow, 1958), flies (Pick and Buchner, 1979), honeybees (Rose and Menzel, 1981;Chittka and Spaethe, 2007), hornets (Spiewok and Schmolz, 2006) and the nocturnal bee M. genalis (Theobald et al, 2007) have pointed towards higher order summation of visual signals as an adaptation for vision at low light levels. Such summation, along with the behavioural and retinal adaptations examined in this study, would enable foraging flights earlier in the morning and later in the evening, albeit with reduced efficiency -a cost that is probably worth paying in the competition for nectar and pollen.…”

“…This would enable the insect to gather more visual information per unit distance travelled. Indeed, tethered hornets reduce their flight speed in dim light (Spiewok and Schmolz, 2006) and free-flying honeybees have been observed to do the same (Rose and Menzel, 1981), but this observation has never been quantified. The nocturnal sweat bee Megalopta genalis, in contrast, approaches its nest at a constant flight speed over a large range of light intensities (Theobald et al, 2007).…”

Activity rhythm and action range of workers of the invasive hornet predator of honeybees Vespa velutina, measured by radio frequency identification tags

“…Thus, the duration of each trip can be accurately quantified with RFID: 95% of the flights lasted less than 1 hr. Flying speeds of V. velutina workers are so far unknown, but in V. crabro , it has been estimated at 1.86 m/s (i.e., 6.7 km/hr) (Spiewok & Schmolz, 2005). If both species fly at a similar speed and considering the average trip duration being 15 min, V. velutina workers probably forage within less than 1,000 m away from their nest.…”

Seeing in the dark: vision and visual behaviour in nocturnal bees and wasps

“…While differing less dramatically, the compound eyes of the nocturnal species are also relatively larger, and typically contain larger numbers of ommatidia, than those of their diurnal relatives (Jander and Jander, 2002). Interestingly, the common European hornet Vespa crabro, which has also been suggested to have nocturnal activity (Blackith, 1958;Spiewok and Schmolz, 2006), lacks all such optical enlargements (F. Jonsson, A. Kelber and E.J.W., in preparation).…”