Effect of light intensity on flight control and temporal properties of photoreceptors in bumblebees.
To control flight, insects rely on the pattern of visual motion generated on the retina as they move through the environment. When light levels fall, vision becomes less reliable and flight control thus becomes more challenging. Here, we investigated the effect of light intensity on flight control by filming the trajectories of free-flying bumblebees (Bombus terrestris, Linnaeus 1758) in an experimental tunnel at different light levels. As light levels fell, flight speed decreased and the flight trajectories became more tortuous but the bees were still remarkably good at centring their flight about the tunnel's midline. To investigate whether this robust flight performance can be explained by visual adaptations in the bumblebee retina, we also examined the response speed of the green-sensitive photoreceptors at the same light intensities. We found that the response speed of the photoreceptors significantly decreased as light levels fell. This indicates that bumblebees have both behavioural (reduction in flight speed) and retinal (reduction in response speed of the photoreceptors) adaptations to allow them to fly in dim light. However, the more tortuous flight paths recorded in dim light suggest that these adaptations do not support flight with the same precision during the twilight hours of the day.
Department of Biology, Lund University, Sölvegatan 35, Lund 223 62, Sweden therese.reber@biol.lu.se.
Therese
T
Reber
Department of Physics, University of Oulu, PO Box 3000, Oulun yliopisto, Oulu 90014, Finland.
Antti
A
Vähäkainu
Department of Biology, Lund University, Sölvegatan 35, Lund 223 62, Sweden.
Emily
E
Baird
Department of Physics, University of Oulu, PO Box 3000, Oulun yliopisto, Oulu 90014, Finland.
Matti
M
Weckström
Department of Biology, Lund University, Sölvegatan 35, Lund 223 62, Sweden.
Eric
E
Warrant
Department of Biology, Lund University, Sölvegatan 35, Lund 223 62, Sweden.
Marie
M
Dacke
D000818:Animals; D001516:Bees / Q000502:physiology*; D005426:Flight, Animal; D008027:Light; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology*
Behavioural adaptation; Bombus terrestris; Insects; Position control; Retina; Speed control; Vision